Purple Thai Devil Crab - eggs???
Hey there! I work at an LFS, and a while back due to a clerical error we
received a big shipment of Thai Devil Crabs instead of micro crabs. Mind
you, not vampire or red claw crabs - these are the big, beefy purple
<Oh my! One of the so-called Soapdish Crabs in the trade, which need to
be packed individually, sometimes even in soap-dishes, to stop them
killing each other!>
Just a little bit not what we had in mind!
<I'll say. Interesting pets, but very much one-to-a-tank creatures.>
Anyways, we had to scramble to figure out an appropriate habitat for
them, and you guys were really useful in finding information for these
fairly uncommon critters. I think I've got my coworkers turned on to
using your site for reliably accurate info.
<Ah, that's nice; thanks for these kind words!>
Out of our original 12 crabs, we've sold down to 3.
We've had them housed this whole time in a brackish setup maintained at
0.01 salinity, and it's been working out well. As their numbers have
dwindled they get happier and more active every day.
<Sounds good. They may be aggressive towards one another, and are
certainly opportunistic cannibals, so keeping these, or indeed most
other crabs, in groups tends to end badly. Since a singleton only really
needs something like a 5 gallon tank, they're not super-demanding in
terms of requirements, but they're definitely not social or community
Due to a maintenance issue with the brackish setup, we moved them
temporarily to an empty freshwater tank we deemed suitable for them,
intending on moving them back in a few days. Within 24 hours, the
biggest crab started practically throwing little yellow eggs across the
We've vacuumed some of them up to keep them safe from the other crabs,
but she just keeps laying them! I can find virtually NO information
Everywhere I've turned I'm finding advice regarding vampire crabs or red
devil crabs, but nothing about Thai Devils.
<Right now, I don't think anyone even knows which species of crab this
That's the main problem here. They may be Geosesarma species, like the
Vampire Crabs. In this species the females carry the eggs until they're
ready to hatch, at which point she dumps them in a freshwater pool,
the tiny crabs hatch out and make their own way into the leaf-litter to
hide away from predators. What might astonish you is that these Vampire
Crab species were discovered and sold in the aquarium trade for many
before scientists had a chance to identify them! Anyway, the Vampire
Crabs were then described as Geosesarma dennerle (the purple species)
and Geosesarma hagen (the red species), which you might recognise as
names of German manufacturers of aquarium equipment. The Thai Purple
Devil Crab remains a mystery to me, at least. Besides Geosesarma
species, there's a good chance it could be one of the rice field crabs,
Parathelphusa species, or else a Syntripsa species like the Syntripsa
matanensis, or else a land crab Cardisoma species such as Cardisoma
carnifex -- all of these have purple colours on them, and do turn up in
the trade. You might care to look up photos of these species and genera,
and see if anything looks particularly close to your chap.>
I guess I'm wondering if any of you knew if this was normal or healthy?
<It's a good sign.>
Do these crabs scatter eggs, and is their egg laying stimulated by fresh
water, or do you suppose she flung them out due to stress from the move?
<Could be either, really. Changes in their environment are often
'spawning triggers' for many animals, indicating, for example, the rainy
Since these crabs are semi terrestrial, they're well able to walk
between freshwater pools, dry land, and slightly brackish pools, and
it's probably worth offering all three habitats, initially at least, to
see which they prefer. Given we simply don't know what species the
Purple Thai Devil Crab might be, it's really hard to state precisely
which spawning or living conditions are optimal.>
If this is healthy or normal, what in the way of special care might the
eggs require if they're fertile?
<If they're fertilised, the eggs will hatch and either larvae or mini
crabs will emerge. If the former, brackish or even marine conditions
will be most likely, but the mini crabs just get on with life from the
get-go, and simply need to be kept away from potential predators, which
includes one another! A soft marshy habitat with lots of moss or leaf
litter is probably ideal, but you might equally try a shallow tank with
warm water, a sponge filter, and various bits of stone or wood for
hiding places and to allow them to climb out of the water.>
Would they need a salinity level like their parents, or do the larvae
start out in fresh water and move on down to brackish later?
<Difficult to say. The mini crab type just get on with whatever's around
them, so salinity isn't an issue. They'll probably spend more time on
land anyway, only dipping in the water to refresh their gills. The
are much more difficult to rear, and probably not worth fussing over.
But to cut a long story short, what usually happens here is the larvae
drift down to sea, or at least some friendly mangrove, develop there,
and then when they have metamorphosed they start working their way back
into rivers or dry land, as the case may be.>
I know this was a bit wordy, feel free to edit it down. There's just not
much I can find online, and while I've been searching for hours the eggs
are still sitting in a bucket of fresh water. I hope they're okay!
<So do I! I'd like to see a photo or two; might help to ID these crabs.>
Thanks for listening,
<Most welcome. Neale.>