FAQs about Horseshoe Crabs,
Related FAQs: Horseshoe Crabs 1, Horseshoe Crabs 2, & FAQs on: Horseshoe Crab ID, Horseshoe Crab Behavior, Horseshoe Crab Compatibility, Horseshoe Crab Systems, Horseshoe Crab Feeding, Horseshoe Crab Disease, Horseshoe Crab Reproduction, & Crustaceans 1,
Micro-Crustaceans, Amphipods, Copepods, Mysids, Hermit
Shrimps, Banded Coral
Related Articles: Horseshoe Crabs: Latter Day Trilobites for
Some Systems & Crustaceans,
Micro-Crustaceans, Amphipods, Copepods, Mysids,
Banded Shrimp, Cleaner
Shrimp, P. holthuisi
Crabs, Squat Lobsters, Crabs, Arthropods,
Pycnogonids (Sea Spiders),
About the only thing
not likely eaten
horseshoe crab and pencil urchin...
Mis-mixed mess -- 10/22/11
So. I recently purchase a horseshoe crab for my 40
<... a tropical species at least?>
I am aware that it is too small of a tank when it grows, but I have
access to a 250 gallon when the time comes, I was reading your
frequently asked questions and I saw one about a school's touch
tank with the urchin eating the horseshoe crab.
well, I have a similar situation.
In my tank, I have a pencil urchin, two clownfish, a damsel, a cleaner
shrimp, coral banded shrimp, sexy shrimp, scarlet and blue legged
hermits, a flame scallop,
emerald crab and the horseshoe. Earlier today I caught the horseshoe
crab swimming around the tank, which seemed strange to me as he was
plenty happy to roam the sandy bed.
<... this is NOT a tropical species...>
My girlfriend came home a couple hours later and found the horseshoe
crab stuck to the urchin, when she pried them apart, half the front of
the crab's "face" was gone, however, the crab is still
alive and doesn't seem much perturbed by the event, as far as I can
tell, is there any hope for it, or is there anything I can do?
<Study ahead of purchasing livestock... This animal can't live
in this setting... the Stenopid will likely eat the other crustaceans,
the Pen shell starve...
What you've jammed together here won't work. Bob Fenner>
Re: horseshoe crab and pencil urchin
thanks for the advice, Buying livestock going by just the reef safe
label was silly of me,
<Happens... all the time>
I'll be sure not to repeat the same mistake.
Thanks for helping out a newbie to the hobby.
<I assure you that you can count on what is archived on our site, in
my written work as reliable. Cheers, BobF>
Horseshoe Crab... sys., sel.
I have spent a lot of time on your website and will not buy anything
for my tank anymore without looking to see what you guys have to say
about it first. I've spent a lot of time the last few days looking
over all the info on Horseshoe crabs that you have, all the questions
seem to be people who bought them and are now trying to figure out what
to do with them, so thus I have not found all the info I am looking
for. I think the horseshoe crab is an amazing animal and am very
interested in setting up a tank for one. I was thinking to use a frag
tank style tank, something at least 4 feet long and at least 2 feet
wide, but only about 16 inches deep or so and setting up the whole
thing as a sand bed for the horseshoe. I would set it up so it shared
water with my reef tank
<... which is coldwater?>
so I could take advantage of the good water quality and filtration and
chiller that I have on that, and add more total water volume to my
system. The drawback of this is that I keep that system @ 76
<This won't work>
I see that the commonly available Atlantic species of horseshoe prefer
colder water than that, are the indo-pacific horseshoes better for
<IF you could secure one of these it might work>
and if so are they ever available and how do i tell the difference
between the species.
<Have never seen offered in the trade. ID info. you can find on the
Also if I can find one that can handle my temperatures how deep of a
sand bed should I set up.
<Four inches or so will likely do for the size of the specimen/s
you'll be able to keep here>
And is there any other advice you would have for setting up a tank
dedicated to a horseshoe?
<All I'm sure of is posted on WWM>
Lastly if this ends up happening, what quarantine recommendations do
you have for horseshoes,
<Mmm, a couple weeks isolation from other systems. Do track
metabolite accumulation in their quarantine system>
I am slightly paranoid about quarantine and have separate quarantine
tanks for both my fish and my corals, nothing goes in without being in
quarantine for a while.
<Welcome. Please do relate your experiences if you go forward w/
this project. Bob Fenner>
Horseshoe crab arriving today, sys. (RMF, thoughts on
releasing Limulus into the wild? I'm against...)<<Am totally
opposed. RMF>> 11/17/09
I read with interest your FAQ section on Horseshoe crabs.
<Fascinating animals indeed.>
Unfortunately, I did so after ordering a 2-3" crab yesterday from
a website that said they are easy to raise and will do well in reef
<Good heavens no!>
I have a 125-gallon reef tank and a 55-gallon FOWLR tank.
<Not a good home for this chap.>
However, after reading your FAQ's, it is clear this new arrival
will not be happy in either place due to the water temp, among other
things. I want to give him the best shot at survival until I can figure
out what to do with him long term.
I have a 100-gallon Rubbermaid tub, 80lbs of Caribbean Live sand still
in the bags, plenty of "seasoned" salt water and cured live
rock, powerheads, etc. I will use whichever of these things I need to
for this crab and will purchase whatever else you think I need for the
next year, short of a new aquarium.
<Actually, maintaining Limulus under lab conditions isn't
especially difficult, and if you Google "Limulus polyphemus"
(the Latin name) as well as Horseshoe Crab alongside
"maintenance" and/or "aquarium" you'll find
there are fairly reliable protocols for keeping these creatures for
extended periods. While not precisely white mice, they are much used
lab animals, particularly for medical research. See for example,
In short, they're kept reasonably cool, room temperature in an
unheated room usually fine, and maintained in a clean, filtered
aquarium. Feeding is done separately, with the animal turned upside
down, food (chunks of fish, seafood, etc.) placed in its
"claws", and then the animal replaced in a tub of seawater.
It's left to feed for about an hour or until its defecated, and
then returned to the maintenance tank. Repeat every couple of days. In
the wild these animals hunt for small organisms within the sand bed,
but this really isn't viable in captivity.>
Please let me know the best way to set up these things to make a
suitable environment for him until he outgrows the 100 gallon
Rubbermaid (by the way, how will I know when he has outgrown it?).
Also, can I release him into the Long Island Sound once he grows and if
so, what size should he be before release?
<I'm not wild about releasing captive animals into the wild. For
one thing, at any number of points along the chain of handling it can
be exposed to parasites, bacteria and viruses that don't exist in
Long Island Sound.
There's also the issue that you may not even have Limulus
polyphemus, with Asian sources certainly sending out Carcinoscorpius to
pet shops in Europe, and therefore possibly elsewhere. Obviously
releasing non-native species is a bad thing. Since these animals do
reasonably well in public aquaria, you might send a couple emails out
to such places, to see if they can home your beastie. Alternatively,
humanely destroy the animal (again, info on this will be in the
scientific, if not hobbyist, literature).>
Lastly, would it be okay to purchase minced clams (like they use for
clam sauce) and chop them even finer for him?
<A variety of seafoods is best, since by themselves seafood items
tend to be lacking in one or other regard. Unshelled shrimps have
calcium but too much thiaminase, shelled cockles are low in thiaminase
but not enough calcium, and so on. The more variety, the less chance of
problems. Lab specimens take standard fish pellets readily enough, and
while there's debate about their use as a staple, as an occasional
vitamin top-up they may have their place. Alternatively, your usual
marine vitamin supplement could be used.>
Thank you for any advice you may offer.
<Hope this helps. Cheers, Neale.>
Re: Horseshoe crab arriving today, more re sys.
Thank you for your prompt response.
I will feed him/her as you propose.
I will set up the Rubbermaid home for him/her for now. According to the
seller, this is an Atlantic Limulus.
<Good to know. Telling the species apart isn't difficult, and a
cursory review of the literature should help if you're
I have an extra submerged pump/filter setup from a small koi pond which
I can use.
Should I leave the bioballs in there or just use the sponge filter?
<Probably won't make much difference either way. These
aren't "delicate" animals provided they aren't
starving or overheated (which are the prime sources of mortality in
Will the crab be okay with the water movement that comes from the top
outlet (used to be a fountain) of the pump/filter setup?
<These animals are used to very strong water currents, but that does
assume they're able to "dig in" a bit. I'd see how
you go. In aquaria they often get pushed onto their backs, in which
case you'll need to right them.>
Should I fill the tub to the maximum level? (100gal)
<More water the better of course, but 100 gallons for a 3-inch
specimen might be overkill.>
The only room I can put the tub in is heated. I will put a thermometer
in the water. What is my target water temp? Should I do periodic water
<Wouldn't worry too much. Unless the water temperature is above
20 degrees C, these animals aren't stressed. Do read that article I
linked for you; it contains details on the established
Lastly, should I not bother opening the two 40lb bags of Live Sand and
just leave the tank with not sand?
<In labs sand is rarely used because of the risk of the sand getting
dirty and causing infections. Since "clean" crabs are
essential for the work being done, this is helpful. But under aquarium
conditions a few cm of
coral sand and crushed coral would be very useful. Live sand is
obviously helpful in terms of water quality management, but the Limulus
couldn't care less either way.>
I also have Live Rock that needs a place to go. Can I put it in the
crabs tub or should I put it in a separate tub?
<Limulus don't like rocks. Plus, below 25 C, your expensive
Fijian live rock is soon going to die back. Would concentrate on
old-school canister-type filtration, ideally supplemented with some
aeration to keep
the water nicely oxygenated.>
Over the next few days I will do the research you propose so I
don't have to ask you so many questions!
<I'm no great expert on these beasts, though like Bob, I've
bumped into them a few times in the scientific side of my life.
They're virtually never kept properly by hobbyists, hence the need
to concentrate on lab reports.>
Right now, I am in a hurry to set up the crab's new home before
FedEx arrives :))
<You'll be fine. These are EXTREMELY hardy animals when given
essentially correct conditions. There is an Asian species sold as a
freshwater horseshoe crab that manages to cling onto life for months
conditions, even though it's a brackish/marine beastie. Don't
panic, do your reading, and enjoy.>
Re: Horseshoe crab arriving today
thanks again! I will give it my best shot!!!
<Good luck! Neale.>
Subject: another photo, please: blue-legged
> Hi Bob,
> Do you have this beastie? Clibanarius tricolor, or
> As a swap, I can offer a photo of Carcinoscorpius
rotundicauda, a euryhaline Limulus doing the rounds as
the "freshwater horseshoe crab" even
though it doesn't last long in freshwater (no surprise).
Will either of the attached do? B
Re: another photo, please: blue-legged hermit?
Yes, perfectly well! Thanks Bob.
Attached, a "freshwater" horseshoe crab.
<Will post w/ your prev. comment with credit to you.
FW Limulus, not! 8/29/2009
Here's a better caption:
"Carcinoscorpius rotundicauda, one of several Southeast
Asian Limulus relatives. Basic care similar to Limulus
polyphemus, except that Carcinoscorpius rotundicauda is truly
euryhaline and tolerant of a broad salinity (and temperature)
range. Sometimes sold as a freshwater invertebrate, as it does
sometimes occur in freshwater habitats, having been recorded from
the Hooghly River 90 km (56 miles) upstream.
However, it does not do well in freshwater aquaria, but can be
maintained in brackish or marine aquaria from SG 1.010 upwards,
assuming other factors (substrate, diet) are
Will append. B
Horseshoe crab, leave at the beach 8/9/09
I have questions because of a very stupid situation, as probably
evidenced by the title, that I need to resolve.
Recently my family brought home a live horseshoe crab this past Friday
(along with about a dozen horseshoe crabs which died upon the touch of
chlorinated water-- the horseshoe crab I managed to get some spring
water for which I added salt).
<They are very sensitive to water chemistry, unless the salt levels
are at the appropriate level, 35PPM, pH, and composition (marine salt
not table salt) then they will quickly die.>
He is literally surviving in a clear plastic storage tub over this
weekend, and we attempted to dump some sardine in there and now a piece
of chicken, as well as one of the dead hermit crabs.
<I would not try to feed him, more likely to just foul the
There is no sand of which to speak and I have changed the water twice
since then. We are hoping to get him back to the beach today but we are
wondering if we will end up shocking the crab, as many marine animals
get easily shocked by temperature changes.
<Getting him back to the beach is his best and probably only chance,
a difficult species to keep even or dedicated hobbyists.>
I've put the crab out on the fire escape in the hope that the water
will more closely match the outside (I realize this is unrealistic but
I still feel it's better than my guesswork).
<Temperature is probably the least of his concerns to be
Since I am assuming he ate neither the sardine or the chicken, we are
also wondering how long he can go without food, and have we
inadvertently debilitated him too long to survive upon his return.
<He can go several days at least without food, best to just get him
back to the ocean as quickly as possible.>
Re: Horseshoe crab, 8/10/09
Thank you very much for your advice. He was returned today, and very
quickly burrowed himself into the sand of the wet shore, which I assume
means he is healthy enough to recover speedily.
<A good sign.>
Horseshoe crab 7/4/08 This is for Bob Fenner, or if
Bob is not there, then hello to whomever is helping me today. I
have had my horseshoe crab, "Dozer", short for bull
dozer, for several years now. He is getting kinda big for my 55
gallon salt water aquarium. He is about 4 inches wide. I only
have one rock and some barnacle shells in the bottom. The bottom
is mostly sand. I have been thinking about letting him go in the
wild where I have seen several adult horseshoe crabs. Is this a
good idea? <Mmm, no> The last time I returned a fish to my
LFS it died there so I don't want dozer to have the same
fate. I figure he would have a better chance in the wild. What do
you think? <That in all (not just the majority) cases,
returning any life to the wild is a poor idea> Secondly, I am
wondering what is the best creature to get to stir up my sand
substrate? I have three percula clown fish, two of them are
breeding. I have two light blue damsel fish, a cleaner shrimp, a
Brownbarred / Banded Goby, a small crab not sure what type, and
some feather dusters. Thank you, and I look forward to your
response. Kathy <Please read here:
http://wetwebmedia.com/marine/maintenance/index.htm the third
tray down. Bob Fenner> Nature is like a spider web - if you
pull on one string, you affect everything else in it P Please
consider the environment before printing this e-mail <Good
spiels... I'd add, "think about the environment before
Re: horseshoe crab 7/4/08 Ok, I am wondering then
what can I do with dozer, he is disturbing my clownfish, knocking
everything over in the tank. I, like many other people, was told
that dozer would only grow to a certain size and then stop
growing (probably they meant that he would just die, but did not
want to tell me that). <Mmm, yes... a fallacy that seems to be
perpetuated forever> Now the poor guy is stuck in a 55 gallon
tank, and I am sure that he is going to shed again soon, and that
is when the real trouble will begin. Should I find a LFS that
will take him, I know of one about an hour away that has some
very big tanks. I am sure that he would be happy for awhile
there, if they feed him. <Yes... Craigslist as well is worth
listing this animal in> I donated one horseshoe crab that got
large, like this one, to the Miami sea aquarium. But they kept
him in the same size tank and used him for educating children
about sealife. Does not sound like the kind of life I want for
this guy. <Alternatives?> I realize now that buying a
horseshoe crab was a mistake, but I need to find a better place
for dozer and need advice on what is the best thing to do for
Dozer. Thank you for your help. Kathy <Thank you for sharing.
It's not just/only non-indigenous species that I and others
are and should be concerned with... even returning native species
to environments they hail from entails risks... principally of
introduction of pathogens, vectors. Bob Fenner> Re:
horseshoe crab 7/4/08 Well we will see, I have posted
Dozer on Craig's list, I have no idea if anyone serious will
be interested, so we will see. I will only give him to someone
who has a large established tank, and who knows how to care for
him. <Good> If I don't get anyone interested I will
take my chances and try to find a suitable place in the wild for
him <Please... don't do this... see my prev. email> as
I think that would be better than being cooped up and starving in
a small tank. If I did not have any fish I would keep him, but I
am afraid that he will eat my fish one day. He eats my snails
that I get to control the algae, so I don't buy them anymore.
He is just too big for me to keep. I certainly will not get
another, even though I love to watch him and find the species
very interesting. Kathy <Ah yes. B>
Horseshoe Crab selection, systems 1/17/06
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>