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FAQs about Horseshoe Crabs 1

Related FAQs: Horseshoe Crabs 2, & FAQs on: Horseshoe Crab ID, Horseshoe Crab Behavior, Horseshoe Crab Compatibility, Horseshoe Crab Selection, Horseshoe Crab Systems, Horseshoe Crab Feeding, Horseshoe Crab Disease, Horseshoe Crab Reproduction, & Crustaceans 1, Micro-Crustaceans, Amphipods, Copepods, Mysids, Hermit Crabs, Shrimps, Cleaner Shrimps, Banded Coral Shrimp, Mantis Shrimp, Anemone Eating Shrimp

Related Articles: Horseshoe Crabs: Latter Day Trilobites for Some Systems & CrustaceansMicro-Crustaceans, Amphipods, Copepods, Mysids, Isopods, Shrimps, Coral Banded Shrimp, Cleaner ShrimpP. holthuisi Pix, Mantis "Shrimp", Lobsters, Slipper Lobsters, Hermit Crabs, Squat Lobsters, Crabs, Arthropods, Pycnogonids (Sea Spiders),

Mini Horseshoe Crab? I Don’t Think So! 9/16/07 <Hi Brandy> I recently purchased a horseshoe crab, it's about an inch in length, including the tail. The store I bought it from says it will stay fairly small, 1 to 2 inches, (but I have yet to read anything stating there are any small species, have I been given incorrect information? <Sadly yes. There are four species of horseshoe crab: Limulus polyphemus, Tachypleus gigas, Carcinoscorpius rotundicauda, and Tachypleus tridentatus, and all reach sizes considerably larger than 1 to 2 inches! More than likely, you have Limulus polyphemus, which is an Atlantic specie (the others are Indo-Pacific). This specie can grow to a foot across and 2 feet long! Unfortunately, because of its size potential and specialized needs, this fascinating little creature has a very low survival rate in most home aquariums. Sadly, most slowly starve to death. Please see this link, especially the FAQ titled “Horseshoe crab Overview 4/14/03” for more information regarding requirements/care : http://www.wetwebmedia.com/horseshoecrabfaqs.htm > Thank you, <You're very welcome, I just wish I could have given you better news! -Lynn> Brandy

Small SW... Horseshoe Crab... No useful info.  – 06/08/07 Hello, I just recently found your site and have learned a great deal from it already. It is a shame that some fish dealers don't have the knowledge to advise people in their purchases in the beginning. <Such is the nature of experience, reality... "Once you get something wired... your chances are generally long over"> I have a 30 gal tank, have had it for 4 years. I purchased a horseshoe crab <What species? Might be at the end of its lifespan for these circumstances...> three years ago. (sadly, after reading your article). It has seemed to do well until the past week. It has molted twice in the time I have had him. He now seems to be in trouble, hopefully I am not starving him, but he is spending a lot of time upside down, his gills do not seem to be moving very often and his shell is soft and has a brown tint on the back that was not previously there. Any help would be greatly appreciated. <Mmm...> I also have a light spotted sea cucumber that I have had for about a year. <Could be a factor here as well...> It recently divided into two separated cucumbers. Both "ends" seem to be doing well but I have not been able to find any information on this. <Need to identify... Pix?> Thank you again for your time and expertise. I will definitely see your page before any future purchases. <Uhh... need more input... system make-up, maintenance, water quality tests/history, foods/feeding... Bob Fenner>

How to Feed My Horseshoe Crab - 4/8/07 About 2 weeks ago I recently purchased a horseshoe crab, that is 1" in size. <Fascinating creatures but have specialized needs.> He only came out at night and not every night until yesterday, when it came out during the day. I wondered if it was hungry, and I read that horseshoe crabs eats worms and mollusks. I went to a seafood store and got a fresh clam. I put the clam in the tank, and the clam is alive. The clam is bigger than the horseshoe crab. The clam is about 2" big. The horseshoe crab has been running around the tank during daylight for 2 days now, burying itself at times. It has bumped into the clam a few times, and it has not seemed interested in it. Is the clam too big? <Yes> Is there a method to get the horseshoe crab to eat it? Do I need to open the clam? <I would instead offer the clam finely chopped, or perhaps mysis, clean blood or Tubifex worms. Please read the FAQ at this link: http://www.wetwebmedia.com/horseshoecrabfaqs.htm . As mentioned, these creatures have specialized needs, so please be sure you can provide them.> Any response will be appreciated. Thank you so much and have a happy Easter. Christian <You're very welcome and the same to you! -Lynn>

Horseshoe Crab Health and Cucumber Fission 4/5/07 Hello! <Hi Susan!> I just recently found your site and have learned a great deal from it already. <Thank you! How may we help you today?>. I have a 30 gallon tank that I have had for about 4 years. I purchased a horseshoe crab, sadly, since I have read your article, 3 years ago. <Wow, considering their specialized needs, 3 yrs in a 30g tank is a long time for one of these guys to survive!> He has seemed to do well until the past week, he has molted twice during the time I have had him. <Depending on his age, he should have molted more than this over a three year period> He now has a dark brown color to his back, his shell is soft and he does not seem to be moving his gills very often.<Did he just molt in the last day? If so, that would be normal. Their shell doesn’t harden for around 24 hrs. If not, that combined with the slow gill action sounds like he’s in trouble. How is everything else in the tank? What are your water parameters, including calcium? Have you ever tested for Iodine/Iodide? Is he still eating and if so, what do you feed him? Also, how large is he now?> He also is spending a lot of time upside down.<Horseshoe crabs sometimes do odd things but all in all, I’m concerned for the little guy> I do hope I have not starved him or caused him other harm. <If he survives, he really needs to be in a tank more equipped for his needs. Please read the FAQ listed as “Horseshoe crab Overview 4/14/03” at this link: http://www.wetwebmedia.com/horseshoecrabfaqs.htm > It is a shame that some fish dealers do not have the knowledge to help educate people on purchases. <Agreed. Horseshoe crabs are wonderfully interesting creatures that in the right setting, can be very hardy. Unfortunately, they’re not well suited to the warmer, predominantly rock filled reef tanks that most saltwater enthusiasts keep> I will not make another purchase without checking your site first. <Yes, it’s a difficult lesson that many of us have learned the hard way, but the good news is that by you writing this, you may be saving another life down the road> I also have a light spotted sea cucumber that recently divided into two sea cucumbers. Both "halves" seem to be doing fine but I have not been able to find any information on this. I would appreciate any help you could give me. <Ha! Thought you were seeing double, didn't you? Actually, "fission", or splitting into two parts in this case, is normal for some species of cucumber. Interestingly enough, these species can reproduce sexually or asexually. What usually happens is the cuke will disappear for a bit, maybe a week or two, then reappear as two separate entities! How neat is that? Here’s a link to our Faq’s on cuke reproduction: http://www.wetwebmedia.com/cukereprofaqs.htm > Thank you for your time and expertise.<You’re very welcome, Susan! -Lynn> Feeding a Horseshoe Crab - 03/31/07 Hello guys! <<Good morning!>> I love your site, thanks in advance for the help here. <<Hope it proves useful>> I recently purchased a horseshoe crab for my tank. <<Mmm...and likely Limulus polyphemus...an Atlantic species>> I have fine sand, fairly deep (3-4 inches), a lot of room for him (75 gallons with little live rock), but I am worried about feeding him. <<75g is not enough room for a mature L. polyphemus...can grow to 12" in diameter>> I read that you are supposed to feed him blood worms/clams/mollusks. <<You can, yes...and a clam "is" a mollusk...as are mussels, oysters, snails, octopi, etc.>> I have blood worms, but I don't understand exactly how him to eat them.  Should I bury them in the sand so when he runs over them he munches them? <<I wouldn't>> Then I am worried that my cleaner shrimp would find it first.  I have also heard about sticking it under his shell.  Do I just grab him by the sides and put the food underneath him? <<Though quite hardy, I wouldn't advise subjecting it to this stressful activity on a continuing basis>> Also where can I buy mollusks?  I'm not really sure what they look like. <<Oh but you do! (see here: http://www.google.com/search?sourceid=navclient&aq=t&ie=UTF-8&rls=WZPA,WZPA:2007-07,WZPA:en&q=mollusks+definition)  Go to your local grocer and pick up some fresh clams/oysters/mussels from the seafood section.  place one of these on the substrate near the horseshoe crab...you can even help it out a bit if you wish by prying the shell open beforehand but this shouldn't be necessary...and as an occasional treat you can also present it with worms/Nightcrawlers from the garden.  And do be sure to remove any uneaten foodstuffs>> Thanks!
<<Regards, EricR>>

Horseshoe Crab/Health 2/9/07 I'm hoping you can help me out. <Hope so, Deborah> I have a 90 gallon well-established salt tank that currently houses five yellow-tail damsels, a striped damsel, and a horseshoe crab.  We have had the damsels for almost two years and the horseshoe crab for almost a year now.  We were lucky enough to watch our horseshoe crab molt and got to save the shell (see attachments).  We are currently fixing a poisonous algae problem and I think it has affected the horseshoe crab.  I found her upside down under one of the filters this morning and thought she was dead.  When I netted her and brought her to the surface, her gills were moving but very slowly.  I put her in an isolation/hatching net (see attachments) and saw that she improved quickly.  Her tail is snapped at the end which I realize she will likely regenerate during her next molt.  Finally, I am getting to the point of my letter.  I don't want to release her until this evening when the bulk of the algae is cleaned but, she has other plans.  In her  attempts to free herself from the isolation box, she keeps landing on her back and can't right herself because of the snap in her tail.  I have spent the better part of the morning flipping her back over.  Do you think it's safe to release her?  How long can she stay on her back safely?  Thanks so much, in advance, for any help you can provide.   <I'd leave the crab in isolation until health improves, eating, righting itself.  Having gravel in the isolation tank will help it right itself.  If you have treated the tank with an algae inhibitor, this very well could have affected the crab's health. Read FAQ's here and linked files above.  Learn here from the experiences of other Horseshoe Crab keepers. http://www.wetwebmedia.com/horseshoecrabfaqs.htm  James (Salty Dog)> Deborah

Re:  Horseshoe Crab/Health 2/9/07 Thanks so much for sending such a fast response. <You're welcome.> It's nice to know that there are volunteers taking the time to help those of us who need it especially when the same LFS who sell these little guys know nothing about them.  I ended up releasing the crab late last night because the tank bottom was cleaned.  A few months ago we found that our substrate was too thick resulting in not enough aeration and it was causing spots of anaerobic bacteria throughout the tank. <Yes, can/will happen.> We removed a lot of the substrate and the problem slowly subsided.  Harry (the horseshoe crab) <Skinhead would have been a better name:)> also helped with that because she constantly moved the substrate.  Recently, the same bacteria came back with a vengeance and we were concerned that Harry would be affected.  We were told by our LFS that we should replace our lights.  I have been telling my husband this for months.  Now, its just a waiting game.  Harry seems to be holding her own but insists on staying directly beneath one of our filters.  As for your response to my original email, we don't use algae inhibitors because normally our tank produces just enough of the good algae to keep our fish happy. <My concern here is the chemical make-up of some of these products that can affect the health of invertebrates.> I wish I could have put gravel in the isolation tank.  It would have kept me from spending the day flipping Harry over.  Its a net tank and just can't handle the extra weight of any gravel.  I've decided to use my spare 10-gallon tank for all future isolation issues.  You're horseshoe crab FAQ's section has been a lifesaver.  We bought Harry on a whim, like so many others mistakenly do (our first unresearched purchase) along with a hermit crab from our LFS.  We knew nothing and could find no information anywhere.  We even went to two large local aquariums and they could not help us.  After many more long hours searching online, we finally found your website!  What a relief we felt.  Your site has been a constant source of valuable information for to us.  This reply needs no response.  Thanks for all that you do for us. <You're welcome, Deborah, and continue reading/learning.  James (Salty Dog)> Deborah Rowe

Horseshoe Crab/Compatibility 1/9/07 Hi, <Hi Joey> I purchased a horseshoe crab a week ago and just today bought some Camel Shrimp...I went to work and came home and just found their heads. <Mmmm cannibals in the tank.> Could my Horseshoe Crab have eaten them or did they die first?? I bought live cured rock today could that have been a problem?? <Well Joey, what else is in the tank besides the Horseshoe Crab?  Horseshoe crabs are mainly sand sifting filter feeders, although there are some species that are more predatory.  Depending on what specie you have, the crab could have very well ate them.  Again, you may have a fish or other invertebrate that had lunch on you.  As for dying first, could very well have happened depending on your acclimation method.  The newly purchased live rock; could have gotten a Mantis Shrimp as a not so nice bonus.> Thanks <You're welcome.  James (Salty Dog)> Joey Horseshoe Crab selection, systems   1/17/06           Ok, first off I have to say I did not do an extensive amount of research on horseshoe crabs before I bought one (and now I regret that very much). I went to one site that said they were easy to keep and ate matter in the substrate.  With this lazy-man information I went to my local fish store and picked one up.  In my obsession with my new horseshoe crab I decided to do more research and came upon this site (which I might add is very helpful).  I feel really bad for my horseshoe crab, I fear he will starve. <Most do> I have only a 55 gallon tank, and about half the sand bed is covered with rock.  The temp is usually kept at 78 degrees Fahrenheit, I'm aiming to lower it (would 75-76 degrees be good or still too warm?). <If this is a/the (typical) coldwater species, (the Atlantic U.S....) yes>   His tank mates are one scooter blenny, one royal Gramma, two peppermint shrimp, one emerald crab, and about a dozen types of snails and maybe ten scarlet reef hermits.  As I now see I believe I cannot support one of these creatures with my sand bed alone like the site said (oh yeah, my sand is sugar fine and about 2"-3" deep, as of now the horseshoe crab is about 1.5" across and .5" tall)  I'm also worried about his health in the present, let alone starvation in the future.  When I first introduced him he had trouble getting under the sand, he would go in half way, and then come out again. <Good description> He was also very clumsy, crashing into walls and the rock and sometimes flips himself over.  I woke up this morning, watched him a bit, and he was finally able to get under the sand, but he's not moving, I can see the lump where he is and he hasn't moved for about 2 hours.  Is this normal? <Do have periods of long senescence> Any way, if he does survive *fingers crossed*, is there a way I can possibly feed him manually by putting food under his shell? <Can be tried> Any other suggestions on feeding are welcome, and what can I feed him to supplement his diet of worms other things in the sand that will be healthy? Thanks for your help! <What little I know re the captive husbandry of these ancient arthropods is posted on WWM. Bob Fenner> Horseshoe crabs  10/5/05 I was reading on your FAQ's about horseshoe crabs that they don't  live long ..days or weeks. I had kept them before in a tank without a  heater (room temp), and they lasted for years. I fed them black worms, and I  would put a little piece of fish under their shell. The tank was fairly warm,  but most of them did ok. <Eddie, the general rule for keeping horseshoe crabs is a larger system with fine gravel/sand and preferably cool water.  As you say, they are not hard to keep provided the correct conditions are provided.  James (Salty Dog)>   Eddie V.

Crustaceans And Damsel Death - 08/12/2005 I'm wondering how my fish died; he was in a 10 g. tank.  He is a neon velvet damsel with 3 hermit crabs and horseshoe crab and a turbo snail. <Way too much life for a 10 gallon tank....  Please see here on horseshoe crabs:  http://www.wetwebmedia.com/horseshoecrabfaqs.htm .  This animal is completely unsuited to your system.> I had only had him for 24 hrs. and he was on his side. <Almost certainly environmental.  Be testing your water regularly.> When the hermit crab saw that he went over there and grabbed him so I took all the hermit crabs out in a small bucket with a bit of water and they ate that entire fish but the head. When they were done I put them back in the tank. Can you tell me if that was okay? <Probably not a problem, in any case.> My horseshoe crab has been buried for I think two or three days but has been messed with to see if he was alive. <Likely not for long in your system....> He was ,then he just buried himself again. Can you tell me the proper care for all of them? I would appreciate it. Thanks,  Drew <All you seek and more is already archived:   http://www.wetwebmedia.com/marine/index.htm .  Wishing you well,  -Sabrina>

Crustaceans And Damsel Death - II - 08/14/2005 I had read a few of your listings on horseshoe crabs would a pet store buy on from. <Might wanna proofread before you send, for future reference....  I am *guessing* you are asking if a fish store would buy back your horseshoe crab?  Possibly, or possibly would take it in trade for store credit.  You will need to check with your local fish stores; all of them vary in what they will do about livestock.> I don't know too much on the subject, I'm only 12. <Ahh, you're doing outstandingly for 12!  Keep up the research, and you're sure to learn and enjoy this hobby.> My hermit crabs are not big and neither is the horseshoe crab.   <The size of the crab is not what's in question, just the pure unsuitability of it in any warm, small, tropical reef system.  The smaller the tank, the worse for the horseshoe.> I have a little castle thingy and a little rock. I have also been cleaning the tank and doing water changes once a week. Should I keep on finding out if the crab is alive or to leave him alone. <I would not mess with him any more than it would take to get him to a fish store or someone with a suitable system.> I also don't have enough money to get a bigger aquarium. <It would take a very large, cool water aquarium to keep the little guy alive.  Were I in your shoes, I'd truck him back to the store and ask for a refund.> I haven't been able to find out about these little tiny things crawling on the glass is that bad or good and what do I do about them? <They're more than likely good.  Probably copepods and other such desirable animals.> Thank for all your help so far, you guys seem to know a lot about fish. <The more you learn, the more you realize how much more there is to learn! What a terrific hobby this is.  I'm glad you're getting into it so young. I'd like to give you a few ideas for your tank.  If you stick with just invertebrates, like your hermits, and maybe a pair of skunk cleaner shrimp, it'll probably be a very easy, very fun tank to care for.  There are a lot of neat, smallish crabs (scarlet hermits, emerald crabs) and neat shrimp that you could choose from to make your tank fun without fish.  But you've got the right idea picking a single small, hardy fish if you do want to have a fish in the tank.  You're on a great road to a great start!> Drew <Wishing you well on this adventure of learning,  -Sabrina>

Lyretail Wrasse Hello, <Hi Jessica> My name is Jessica and I have a question about housing certain things together. Is it possible to house a horseshoe crab in the same aquarium with a lunar wrasse? Thank you very much.  <I wouldn't. They are an aggressive fish and crustaceans is on the menu. James (Salty Dog)> 

Horseshoe Crab Hello!  I just read your entire FAQ's about Horseshoe crabs.  I am still very concerned about mine.  We did not see the Horseshoe crab very often, only at night.  Since I have added about 50 more pounds of rock, he is visible on a daily basis for many hours. Today he has been "crashing"  everywhere, into the glass, into the rocks, into the jet stream and was even  pinned against the glass because of the jet stream.  He has been doing this for several hours.  What is wrong with him? He does go under the sand periodically but not near what he used to do.  Should I be concerned?   Do I need to move the rock?  Help! Thanks so much! DaisySteel <Daisy, I'm thinking there may not be a sufficient food supply for the crab.  Did you treat the tank with any medication recently?  They also have a unique cycle for breeding and maybe that may have triggered the behavior.  James (Salty Dog)> Horseshoe crab I inherited a horseshoe crab. It has developed a black "fungus?" on its back (near the tail). It is approx. 6" wide and living in a 2 gallon tank...do you think it has outgrown the tank? <Hello, the black fungus is probably algae that has grown from being in such a small tank. A horseshoe crab that size needs at least a 120 gallon tank. Good Luck MikeB.>

Horseshoe Crabs I've recently ordered some small 1-inch horseshoe crabs for an established saltwater tank (with a few damselfish and a Hawkfish). <I do hope that your tank is quite large (~180 gallons or more), as Horseshoe Crabs are unsuitable for life in a small aquarium, even if they are purchased small (everything has the right to grow, right?)> The bottom is mostly rocky now, so I'm thinking I will need to make a sandy area for the crabs to burrow in, am I right? <Yes, your assumption is correct.> How deep should this sand ideally be for the crabs? <Depends on their size. At a small size, I would think around 3" would be plenty. At adult size, you may need a couple of feet.> Also, I've done a lot of research about diet, and have gotten quite a variety of answers. In your opinion, what works BEST with horseshoe crabs, and how often should I feed them (I know overfeeding can kill). <They are detritivores, so fish food/krill would work fine.> Thank you very much-- these are such weird creatures that it's hard to find specifics! <I'm glad I could help. Mike G> We're Not Doctors, Jim! Blood of the Horseshoe Crab for Crohn's >hi my question is regarding using the blue blood as a treatment for Crohn's disease.   >>Hi, no one here at WetWebMedia is qualified to even begin to answer your question.  Our service encompasses advice *only*, and only that which pertains to the husbandry involved of a particular species or group of species.  We would also like to remind those emailing us to *please* use proper capitalization and punctuation.  Marina

Horseshoe crab  Dear Bob, <Michael here today, not quite as good, but I'll do in a pinch>      I live in Rockport, MA and I'm going to set up a 20 gallon, room-temperature saltwater aquarium for local species.  It will contain local seawater and sand.  Some species I'm planning on having are mummichog minnows, common periwinkles, rock gunnels, and hermit crabs. <Neat - possibly some local alga as well?>  I was wondering if a store-bought horseshoe crab could survive in such a tank.  Horseshoe crabs are occasionally found in my area, but are uncommon and usually large.  I know feeding can be a problem, but I plan to use local sand from the ocean full of living things.  I could also use native seaworms.  If you have an comments, or suggestions for other species that could survive in such a tank, please reply.  <Well horseshoe crabs aren't all that difficult to keep alive, but they grow much too large for a 20 gallon aquarium.  The carapace of a horseshoe crab can be 12" across> -Curtis  <M. Maddox>       

Re: Horseshoe crab Michael, Thank you!  I am amazed by how quickly you responded. <Thanks, thought I'm not always this vigilant>  If the horseshoe crabs got to big, I'll just release them where I've found others. <As long as they're endemic to the area, and you release them when they attain ~5" they should do fine>  Do you know any good sites with horseshoe crabs? <I would search Google for some links for you but this computer is going haywire.  I hope I can even get this email sent>  Also, do you know if tidepool Sculpins or cunner wrasse could survive at room temperature?  Do you know of any tropical species that could? <Depends what you mean by room temperature.  Most tropical fish will survive in 75-85 and do quite well> Thanks again -Curtis <M. Maddox>

Horseshoe crab 3/19/04 I recently bought a horseshoe crab.  I've got him in my reef tank it consist of crushed coral and sand , it is mixed about half and half.  I was just looking around the net and had read that they do not do well in captivity because they usually starve.  I also read that they will eat different frozen foods that I can feed him but my main question is that if they die do they excrete a poison like the cowfish would when it dies. because I don't want it to harm my other stuff in the tank. please help!!  thank you Angie <Don't worry about the horseshoe crab poisoning anything else when it dies.  Yes, they often starve in aquaria for lack of natural food, but the bigger issue is that they are temperate.  Normal tropical aquarium temperatures are therefore stressful to the point of being fatal.  Best Regards.  Adam>

Spiders with Shells? hi there, <hello! Ryan with you> I want to know where I can buy the larger sized dried horseshoe crab shell (more than 6 inches wide).  my interest is to paint pictures on them.  so I would want the smoothest-surfaced variety available, rather than some I have seen online that are quite craggy in topography.  what is a fair price for these shells.  I am in California, are there any available here, or would they come from the east coast?  I am seeing them priced at $20 and up plus shipping and handling.  this seems high to me. <Horseshoe crabs, provide a habitat for many smaller crustaceans- Barnacles, Mussels, etc.  This is likely why they're not always a "Paintable" surface.  The shells of these unlikely arachnids also contain Chitin, a chemical used to speed healing.  Lysate, also found in their bloodstream, is used to treat spinal meningitis.  Add the fact that they are a member of the endangered species list: This is why they're highly valued.  I'm sorry that I can't point you in the right direction for a retailer, but one doesn't seem to exist.  Perhaps a running wanted ad on Craigslist.org is your best bet? Cheers, Ryan> thanks for the help, Dave

- Vanishing Horseshoe Crab - Hello, sorry to bother you once again but I have three quick questions.  I put a baby horseshoe crab in my 44 gal about 4 days ago and I haven't seen any signs of him since.  My inhabitants include: 1 Longspine Black Urchin 1 Baby Horseshoe Crab?? 1 Coral Banded Shrimp Numerous Snails and Hermits 1 False Percula 1 Valentini Puffer About 22# of LR (I'm getting more) Is it possible one of these guys ate my horseshoe crab (specifically the coral banded shrimp or the puffer)? <Not without any evidence... bits and pieces laying about.> My next questions involve my urchin, I noticed when I was doing my weekly water change that every time I put a little bit of water in, the Urchin would excrete this white 'goo' for lack of a better description.  Is this similar to what Sea Cucumbers do and is it harmful? <Coincidental, but likely a spawning event - urchins do this every so often. Not the same as cucumbers.> And lastly, will my urchin kill my live rock, only recently did he move from the glass to the rock. <No. Cheers, J -- >  

Question About Horseshoe Crab I recently purchased a 1 inch horseshoe crab for my saltwater aquarium a week ago, and it died suddenly. I had a Damsel with it and  the damsel is doing  just fine. I read your article on horseshoe crabs and saw that you should feed horseshoe crabs blood worms ,mollusks etc. The lady at the pet store said that they eat fish food , and so that's what I fed it. Do you think that my horseshoe crab died because I was feeding it the wrong food? Thanks so much for helping.<I don't think it could of been the food you were feeding but it could be that you overfed.  You need the check your water parameters before you do anything else.  You can read more at www.wetwebmedia.com Cody>

Horseshoe crab Overview 4/14/03 Hi I was looking around wet web media and didn't see any articles on horse shoe crabs like what they eat and size so I was wondering if you could tell me or point me in a direction of where it would be on your web site thanks JM <the following is a bit that Bob and I recently penned on this creature. Best regards, Anthony: Caption for photo: "Horseshoe crabs are not true crabs at all, but actually much more-closely related to spiders. They are also inappropriate for mixed invertebrate aquariums for many reasons. These "crabs" need to be kept in large, specialized (non-reef) systems that are have great open surface area and sand of depth. Definitely not recommended for casual keeping in small home aquaria with coarse sand and dense rockwork. The most commonly available species, Limulus polyphemus commonly ranges from Nova Scotia down to the Gulf of Mexico and grows to 2' long X 1' wide (60 cm  X 30 cm). Several other species are seen in coastal waters from Japan to Indonesia, but do not appear in the US hobby." Overview of Limulus polyphemus By any definition, horseshoe crabs are ancient relics of the past. They have not changed much in the last several hundred million years dating back to the pre-Cambrian era (and are closely associated with their fossilized relatives, the Eurypterids). It is no wonder why they are described so often as "pre-historic". The design of their body has facilitated their long survival through the ages with its strategic and fully encompassing hard shell. Limulus are also extremely hardy in the present wild... enduring severe extremes of temperature and salinity. They are also said to be able to suffer seasonal famine and live without food for as much as a year! A year is also about how long it takes for these crabs to starve in mismatched marine aquariums. Too often, horseshoe crabs are placed in small aquaria with lots of live rock and not enough sand to burrow, forage and survive. Mind you that an abundance of live rock is very beneficial for reef aquariums. The problem is that these creatures, though, do not live on the reef proper. They do live near the reef, however, and will thank you very kindly if you provide a large open bed of deep fine sand for them to dig in. It takes perhaps 10 sq. ft per crab of more at >6"/15cm depth). It is interesting to note that horseshoe crabs may stay buried in the sand for days or even several weeks at a time. Let's be very clear that they live or die in captivity by the presence of deep fine sand and mud and the food they find within. We recommend using finely minced clams and clean Tubifex worms (live or thawed frozen) as part of the staple diet for this creature in captivity. Other ocean meats may be taken with equal enthusiasm. Be very mindful of the size and composition of food offered; Limulus have no jaws to chew or crush prey but instead process food with bristles at the base of their walking legs (yes... they must walk to feed, as the food is passed and mashed by these bristles). Although hardy and peaceful in their natural habitat, these "crabs" do not fare well in captivity outside of large, mature specialized aquaria. They tend to linger for some months in captivity, but again, do not survive past a few months with casual care. Limulus are not true crabs at all, they are rather distant relatives of the spiders, scorpions and even the lowly ticks. Aspects of their phylogenetic relationships are suggestive when you observe their anatomy. The most obvious similarity is their prominent pair of compound eyes. In fact, in addition to the conspicuous pair of compound eyes, these crabs have a second pair of simple eyes on the front side plane of the body. A horseshoe crabs vision is not for feeding however, but for evading predation and finding mates. It is estimated that their range of sight is about 3' (~ 1 meter). Limulus also have 5 pairs of "walking" legs and two specialized pair for feeding and pushing sand, the forward pair on males being distinctly thicker and larger. Perhaps the most distinguishing part of these creatures is their telson (tail). This aspect of their anatomy performs like a rudder for balance and navigation as well as providing ever-important leverage to right themselves from a vulnerable overturned position. Its also quite a formidable weapon (although not its primary purpose) with spines and "timeliness" when thrust erect to ward off a would-be attacker. Despite the armor, horseshoe crabs are in fact rather peaceful creatures. They seem to be fairly indifferent to each other and anything that's not interested in eating them. They are somewhat generalized scavengers that consume many different things strongly preferring polychaete worms and mollusks in the sand. Their natural feeding habits keep them very active at night though in captivity they are willing to feed most anytime of the day if stimulated. This is a large part of the reason why they starve in most aquaria- few are placed into systems with aged, deep mature sand beds that have adequate populations of food organisms to sustain them. It is estimated that Limulus grows approximately 25% with each successive molt for roughly the first decade of life until they reach maturity. Molts occur every 7-10 months naturally. Reproduction is a bit of a ritual during high tide (full and new moons) in the spring or early summer each year. Droves of Limulus migrate to the shoreline to spawn and lay staggering amounts of tiny green eggs. A large female may lay as many as 20,000 eggs which are deposited in a series of holes that she digs along the water line. Copulation is a bit of an interesting display. The males of this species (characteristically smaller than females by about 30%) grasp a hold of a female as she leaves the water to make this run. They are dragged along as the females climb up the shoreline and fertilize each batch of eggs as they are pulled across each pit dug by a female. Wave action covers over some of these nests but numerous Limulus eggs are contributed to the food web above and below the water (fish, birds, etc). In aquariums, many fish will prey on small and young horseshoe crabs. Their chitinous shells have not become sufficiently hardened and they will suffer from repetitive harassment of even curious fishes like large tangs and angels. It should be no surprise that triggers, puffers and eels will readily predate them. It is also quite unnatural for them to be kept with cnidarians and forced cohabitation will usually lead to Limulus dying in the tentacles of an anemone, or large polyped coral. Keeping these crabs in captivity also has very practical implications for their metabolism and increasing size. Before you purchase one, ask yourself if you have the means to keep them as an adult as 16"- 24" (40-60 cm) if and when they are ten years old? If you plan for a full healthy life and lifespan for this creature as you would for any other household pet like a dog or cat, you will quickly realize the very special needs of this fascinating "crab". Our purpose here is not to discourage the popular keeping of this marine creature, but to discourage the improper keeping of it. In a simple sandy lagoon or shoreline display, Limulus polyphemus are remarkably easy and entertaining to keep. Horseshoe crabs- beyond aquaristics: Although Limulus polyphemus are still observed in great numbers, natural plights and human activities have impacted their once abundant populations. Some states in the US have established protected Limulus sanctuaries on assigned beaches. These agencies have sadly followed the lead of governing bodies before them forced to protect their natural resources like the Japanese with now endangered Limulus. The US Federal government has even imposed regulations on the bleeding of horseshoe crabs for improved survivability on catch and release. The unique blue blood from horseshoe crabs has been studied for about fifty years for its remarkable medical properties. Research has focused on anti-bacterial and anti-clotting aspects and the substance known to medicine as Limulus amoebocyte lysate (AKA- LAL). An injured crab uses this substance to quickly clot and disinfect a wound. Medical science uses it to verify that human drugs are bacteria-free and safe. Blood harvested for this research is said to fetch $10,000-15,000 per quart! Sounds to us like somebody needs to either discover how to synthesize it, or how to breed Limulus commercially. Horseshoe crabs have other economic and research values. Their eyes have been studied to enhance our understanding of how the human eye works. Chitin (chitosan) in their shells can be used to manufacture contact lenses and cosmetics and is also said to have nutritive value in homeopathic treatments. Commercially is has been used as a metal sponge in waste water treatment, and medically is can be used to make hypo-allergenic sutures for surgery. Numerous other uses are being researched from this unassuming yet valuable creature. Conservation starts at home as they say. As aquarists, please be mindful of your contribution to the use of this precious living resource. Good aquarium husbandry of this and any animal we keep serves the species through improved awareness and understanding. Fenner and Calfo 2003

Re: horseshoe crabs Hi I read the paragraph it seems its directed at only one species. I'm not sure what I have its light tan and about 2-3 inches in length I have about 7 inches in the back of my tank with lots of sand that he has left trails through would this be a small one that don't get big or a gigantic one? I told the pet store lady my tank was 30 gall long and she recommended him? what do you think. Thanks guys for all my question. <Most all anyone sees in the trade in the U.S. is Limulus polyphemus... they do get large. Bob Fenner>

Horseshoe Crabs Surprise surprise, false information from my LFS. So now I turn to people I can trust. Hello Bob (or who ever may be filling in if unavailable). Ok. I just purchased 2 horseshoe crabs for my tank. I have read through the information you have on your site and they really are some pretty cool creatures. First, I was told that these are reef safe - I haven't found anything that says they are not but just wanted to be sure. <What sort of reef? Not tropical ones...> Secondly I was misinformed about what they eat. Now I see that they eat worms and mollusks. Is there a certain kind of worm (and will they eat fireworms?). There are also 4 different classes of mollusks. Do they eat all of them or only certain ones? <Many types of worms, smaller mollusks of all kinds> Do you know of any kind of foods for them that one can easily purchase? <I would search on the Internet here... these animals are used extensively in research... depending on your filtration, tolerance for different types of pollution of the rest of your livestock... you will find there are choices> I have read in some of your Q&As that these are not a good purchase.  <Yes, agreed> Well, it's too late now and I want to make sure that they do well and don't starve to death. I am also trying to determine what one could do with them when they get to big. Maybe I could donate to a zoo or something like that. <Or back to the shop whence they came?> Oh, one last thing. About their growth, I know some marine life can grow large but don't due to the size of the tank. Are these like that or will they just keep growing? <They generally don't live long in captive care, but can/do grow very large in the wild. Bob Fenner> Thanks in advance, Steve

Horseshoe Crabs Hey I have a 120 gallon fish only saltwater aquarium. Just recently I purchased a horseshoe crab from my LFS. There it was walking around on the sand and acting fine. When I introduced it to my aquarium it went straight under the sand. He has only came out once at night that I have seen. I have had him for about 4 days now. Is that normal? <Yes> If not what should I do? Will he ever come out? <From time to time, particularly when he has eaten everything in your sand bed and runs out of food.> The other fish in my tank are a Small Volitans Lionfish and a Foxface. Thanks for all the help in advance. <You are welcome. -Steven Pro>

Horseshoe Crab Hello WWM crew, I wanted to see if you could help me out. My girlfriend insisted on buying a horseshoe crab which has been living with us for about a month know but about 2 weeks ago we switched tanks from a 110 to a 180 gallon tank and as the 180 cycles with the Damsels we have the horseshoe crab in a 20 gallon tank with some of the old sand. My question is what do these guy's eat ?  <hmmm...somewhat scavenging omnivores that favor clams and worms... do check out the following link: http://www.marinelab.sarasota.fl.us/WHORSESH.HTMon/> Should I just drop some brine shrimp? <frozen adult brine shrimp are a dreadful food. They are nutritively barren... essentially water in the shape of a shrimp. Your horseshoe crabs, fish, etc will "starve to death" (die of a deficiency) if brine shrimp make up any significant part of their diet> I'm getting worried that he may be starving to death since he doesn't move as much as he use too. <Agreed... they are very active at night and can starve in a matter of weeks without regular/daily feeding> Thanks. <best regards, Anthony>

Horseshoe Crabs First off, great informative website! I have had a 3"-4" live sand bed now for a month in my 25tall tank(1year old) and EVERY hair of that dreaded hair algae has disappeared. <Good for you. DSB are quite beneficial when properly constructed and maintained.> I do weekly 5gal water changes which makes up mostly all of the attention I give my mini-reef other than feedings). I have 2 of each: cleaner, peppermint, camel shrimp, yellowtail damsel, green Chromis, and 1 rock blenny. I just added a horseshoe crab that's the size of a 50cent piece, was that dumb? I didn't find info on this site and I bought it cause it was pushing the sand around in its tank like it loved it. <In general, not a good thing to buy something you admittedly know little about. The FAQ for these animals is here http://www.wetwebmedia.com/crustfaq.htm -Steven Pro> Now in my deep sand it just buries itself and hardly ever comes out. Thanks for all your previous successful advice, Nelson

Horseshoe crab Does a horseshoe crabs tail regenerate? <Yes, with successive molts. Bob Fenner>

Horseshoe crab Hi Anthony, <cheers> Sorry to bother you again.  <no bother at all> Do you know anything about horseshoe crabs?  <yes... the husked shell of a large dead adult crab looks just like a Nazi helmet perched atop a man's head> Is it usual for them to hide in the sand for periods of time?  <perfectly natural for short periods> Mine would buzz around the tank some of the time,  <when you first got him (days) or are we talking months? Days is normal> but has been in hiding for a day. I know they are night creatures,  is it possible that he comes out when I have gone to bed?  <exactly> Should I go looking for him, or leave well enough alone? <if your temp is under 80F, leave well enough alone. They don't favor extended high temps, but they are very hardy and adaptable. They also prefer finer substrates (sugar sand)> Thanks again, Kathy <quite welcome>

Horseshoe crabs Robert I have recently acquired a horseshoe crab.  He tends to float upside down a couple times a week. I just tip him and he falls back down. Why does he do this or is this just a normal thing?  <Likely the latter. Horseshoe crabs "do" seemingly strange behaviors... even when there is plenty of oxygen, an absence of noxious effects...> This is the first time for a question to you but I have only been a member for 3 weeks. Thank you for your educated answer ahead of time. <Thank you for your input my friend. Bob Fenner> Kyle Rubarts

Horseshoe Crabs Well, I wasn't expecting that one, but then again I went by Boo for 5 years in college, long story involving a late night of drinking and a young lady, now that I think about it, who reminds me of stomatopods... <Boo? And a young lady... all sorts of images (non tasteful) are coming to mind...> On another topic, I've seen several places offering horseshoe crabs as sand stirrers, from what I gather these are coming out of the Caribbean and Gulf of Mexico, do you have any idea as to how large these guys get? <A couple of feet in length/diameter if they live... not good choices.> I remember seeing some rather large ones (well over 12" across) when I was a kid and we'd go to Assateague National Park. I'd certainly rather not put something that'll grow that large into the 300g I'm planning, it certainly wouldn't be fair to cramp it up that much. OTOH, if they only get around 3"-5", would they make a good sand stirrer? <There are better choices... see the "Sand Stirrers" section on our site. Bob Fenner>

Horseshoe Crabs Bob, Thank you for responding to my last couple of e-mails. Your advice is greatly appreciated! I just added 5 horseshoe crabs in my 100 g. tank to help stir the substrate. Three of them disappeared into the sand as I thought they would but there a couple that keep flopping around and swimming in circles. They start to go under the sand and then they come right back out. Sometimes they end up on their back. They will turn themselves over after a while. It is tiring to watch...I feel like I need to help them out. It's like they don't know what they are doing. Is this normal?  <Yes... normal... they even do this in the wild! Hard to understand how they've made it all these eons...> Will they eventually get under the sand? <Maybe... some stay on top... others perish. Bob Fenner> Thanks so much for taking the time. Cathy M.



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