Rainbow Vampire Crab (Geosesarma sp.)

Choose the Rainbow Vampire Crab, a jewel-coloured land crab for a paludarium

The Rainbow Vampire Crab is a tiny, brightly coloured crab of the genus Geosesarma, one of the land-living "vampire crabs" that have become favourites for planted paludariums. Our photographs show why it earns the name: a deep purple shell that turns orange-red along the front and sides, purple claws, dark purple legs and large, glowing yellow eyes. It spends most of its life on damp ground among moss, roots and leaf litter, and comes down to the water to drink, moult and forage.

Vampire crabs are not aquatic animals. In the peer-reviewed description of the two best-known trade species, Peter Ng, Christoph Schubart and Christian Lukhaup found the adults living on moist banks and valley slopes near small streams in central Java, hiding under rocks and in dense vegetation and sometimes digging burrows at the water's edge, while the juveniles stayed close to the waterline. A Rainbow Vampire Crab therefore needs a paludarium with plenty of land, a shallow pool of fresh water, high humidity and a lid that seals.

Check what the trade name tells you

Vampire crabs were kept by hobbyists for years before anyone knew what they were. Dealers variously claimed they came from Sulawesi, Java, Krakatau or the Riau Islands, until the 2015 paper described the two most common trade forms, the cream-and-violet Geosesarma dennerle and the dark-brown-and-orange Geosesarma hagen, and showed that both are native to central Java. Practical Fishkeeping reported that the two species were named after the aquatic companies that supported the expedition. Many other colour forms, including this one, are still sold without a species name.

Tell it apart from our purple vampire crabs

The Rainbow Vampire Crab is easy to confuse with the Purple Vampire Crab, Geosesarma dennerle. The scientific description of G. dennerle records a violet-purple to purplish-brown front half, a cream to yellowish-white rear half, bright purple claws and bright yellow eyes. The Rainbow form is sold separately, with orange on the shell rather than cream. A colour name alone cannot prove a species, so keep the two in separate enclosures rather than assuming they will mix or interbreed.

Know what you receive with each Rainbow Vampire Crab

• One live Rainbow Vampire Crab per purchase, in the standard size we currently import.
• The sex is not chosen or guaranteed; see below for how to check it.
• Colour varies between crabs, and the scientific description notes that colour patterns in vampire crabs vary considerably even within one species, so the photographs show the form rather than the individual crab.
• Arrival days and our Live Arrival Guarantee are on our delivery and Live Arrival Guarantee information page. Set up the enclosure before you order.

Sex the crabs and plan a small group

OATA explains that crabs are easy to sex by the flap folded under the body: narrow and pointed in males, much wider in females. The Fishkeeper profile adds that males typically have larger claws and can be territorial, and recommends one male with several females unless the enclosure is very spacious. To build a group, buy several crabs, sex them on arrival and be ready to move extra males to a second enclosure.

Plan a paludarium around a very small crab

Vampire crabs are small. In the 2015 description, adult shells of the two Javan species measured roughly 1.1–1.5 cm across. Hobby sources quote larger figures: Practical Fishkeeping gives a body length of 2–3 cm and the Fishkeeper profile a maximum of 3 cm. Because our Rainbow form is not identified to species, expect a crab within that range. Small does not mean a small enclosure, though: these crabs use the whole floor, climb roots and need separate hiding places. OATA recommends at least 60 litres for a small group of crabs and a tank as long and wide as possible.

Use a three-step space check

1. Floor: start at 60 litres (OATA) with a long, wide base; our tank volume calculator converts measurements into litres.
2. Land: the Fishkeeper profile recommends about two-thirds land and one-third water.
3. Hides: give every crab at least one cave, cork tube or root tangle of its own, plus spares for moulting.

Build moist land, mossy cover and a shallow pool

The Fishkeeper profile describes the natural habitat as rocky caves and small burrows on valley slopes beside a stream, with shallow, warm water and roots and plants to climb. Recreate that: a sloping bank of sand or soil with roots, terrestrial or marginal plants and rocky caves; a shallow pool deep enough for the crab to submerge fully when it moults; and Java moss growing both in and out of the water to give cover and easy routes between land and pool. OATA adds that the land should be built from sloped rocks, pebbles and gravel capped with sand, with live plants, roots and caves.

Divide the enclosure by function

Keep the air humid without making a swamp

Practical Fishkeeping describes vampire crabs as kept in high humidity, and the Fishkeeper profile notes that they bask in humid air. A close-fitting lid, damp moss and a moist land surface keep humidity up; a small ventilated gap covered with fine mesh stops the air going stale. Our vampire crab buying guide explains how to balance humidity and ventilation, and why condensation on the glass is not a reliable measurement. A simple hygrometer on the land area tells you much more.

Fit an escape-proof lid before the crabs arrive

Vampire crabs climb everything. OATA warns that crabs are very good at escaping and that a secure lid must be fitted with every hole blocked, and the Fishkeeper profile calls vampire crabs great escape artists and says a tight-fitting lid is essential. Because a Rainbow Vampire Crab is so small, gaps that look harmless are wide enough for it, and once out it soon dries out.

Close every gap with a five-point check

1. Use a lid that sits flush on all four sides; the same lid holds humidity in.
2. Seal cable and tube cut-outs with foam, and cover ventilation openings with fine mesh.
3. Run cables and airline from above so they are not climbing ladders.
4. Close the lid straight after feeding and misting.
5. Count your crabs at dusk, when they are most active.

Keep the pool clean and the water values steady

Vampire crabs live by fresh water, and the sources agree closely on temperature. Practical Fishkeeping and the Fishkeeper profile both give 22–28°C, and OATA gives 22–27°C for crabs in the trade. The Fishkeeper profile describes their water as hard and alkaline, while OATA's general crab values are slightly softer.

Much of the UK has hard, alkaline tap water that suits vampire crabs well, but supplies range from soft to very hard by region, so test pH, GH and KH first. Treat all water, including water for misting, with a tap water conditioner. Our water parameter matcher compares your readings with the crab's needs, and the water chemistry guide explains the terms. Remember that a heater in the pool warms the water, not necessarily the land, so check the temperature on the land as well.

Follow a weekly maintenance sequence

1. Test ammonia, nitrite, nitrate, pH and hardness weekly, as OATA recommends.
2. Change at least 25% of the pool water weekly (OATA); in a small pool, more often is easier than more at once.
3. Clean the land: remove uneaten food and mouldy leaves, and replace leaf litter as it breaks down.
4. Rinse the filter sponge in removed tank water, never under the tap.
5. Check humidity, the land temperature and every lid seal.

A small pool turns toxic fast if the filter is not mature, so cycle it before the crabs arrive; our guide to the nitrogen cycle explains how. Put a sponge over any filter intake so a small crab cannot be trapped.

Feed an animal-rich diet in small portions

Vampire crabs are omnivores with a strong appetite for animal food. In the wild, the 2015 description found that their diet consists mainly of small insects on the ground, such as grasshoppers, and probably also midge larvae and plant detritus. Practical Fishkeeping notes that meaty prey makes up much of the diet: the crabs accept dry food, freeze-dried foods, earthworms and springtails, hunt live house crickets, and at night graze on mosses and algae. The Fishkeeper profile adds bloodworm, mysis shrimp, finely chopped krill or prawn, vegetable matter, fish pellets, algae wafers and specialist crab foods.

Build one measured meal

OATA advises feeding crabs once a day and leaving food for about 30 minutes before removing what is left. Vampire crabs are crepuscular and nocturnal (Practical Fishkeeping), so feed at dusk, when they come out. Place tiny portions on the land near each hide so that a subordinate crab does not have to cross a male's territory. A live springtail colony on the land, such as our springtail culture, gives the crabs something to hunt between meals and helps clear mould and leftovers.

Introduce the crab gently and watch the first week

Check that ammonia and nitrite read zero and that temperature and humidity are stable before the crabs arrive. Use OATA's floating-bag method: switch off the lights, float the closed bag in the pool for 10 minutes, then add small amounts of tank water to the bag over at least 30 minutes. Release the crab at the edge of the pool, next to moss or cover, with as little bag water as possible, so it can walk straight onto land. Our acclimatisation guide explains the method in detail.

Use a first-week checkpoint plan

Keep a species-only enclosure

The Fishkeeper profile rates vampire crabs as non-community and says they are best kept in a species-only tank. They will hunt small fish, and slow bottom-dwelling fish should be avoided; some keepers have kept them with small, fast, peaceful fish. OATA's general advice for crabs is to keep them in a dedicated set-up because they are opportunistic hunters. Our own buying guide adds that different vampire crab forms are best kept apart, because a shared colour is not proof of the same species.

Our tank mate checker is useful if you are still thinking of adding anything else. If you would like a different colour, keep it in its own enclosure: compare the Red Devil Vampire Crab, G. hagen, the Violet Vampire Crab and our Vampire Crab Colour Mix, or see all our Geosesarma vampire crabs, the wider crayfish and crabs category and our shrimps and crustaceans.

Protect moulting crabs and act on changes

Crabs grow by moulting, and the Fishkeeper profile notes that vampire crabs need water deep enough to submerge completely while they moult, and rocky caves to hide in afterwards. OATA warns that the shed skin can look like a dead crab, so look closely before removing anything. A newly moulted crab is soft and defenceless for some days; leave it alone and make sure other crabs cannot corner it. All crabs are very sensitive to copper, so use only treatments labelled safe for invertebrates (OATA).

Pair each observation with an action

Breed vampire crabs without a larval stage

Unlike many crabs, vampire crabs have been bred in home enclosures. The Fishkeeper profile explains that the female carries her eggs under her abdomen for several weeks and that there is no larval stage: miniature crabs hatch directly, stay in or near the water at first and become more terrestrial as they grow. The 2015 description recorded a female carrying eyed eggs about 1.5 mm across. Practical Fishkeeping reports that females carry eggs about every six months and that about 50–60 young hatch from each clutch.

Raise the young safely

The wild juveniles in the 2015 study stayed close to the waterline, so give young crabs a shallow edge, dense moss and plenty of tiny food such as springtails and crushed pellets. Young crabs are small and vulnerable to adults, so a separate rearing tank improves survival. Keep only one colour form in a breeding enclosure so you know what you are raising. OATA notes that smaller crabs often live only a couple of years, so breeding is the best way to keep a colony going.

Answer Rainbow Vampire Crab buying questions

What is a Rainbow Vampire Crab?

It is a small land-living crab of the genus Geosesarma (family Sesarmidae) sold under the trade name Rainbow Vampire Crab. Our photographs show a purple shell with orange-red sides and front, purple claws, dark purple legs and bright yellow eyes. The species behind this trade name has not been identified, so we list it as Geosesarma sp.

Is it the same as the Purple Vampire Crab, Geosesarma dennerle?

Not as far as anyone can show. The scientific description of G. dennerle records a violet front half, a cream to yellowish-white rear half and bright purple claws. The Rainbow Vampire Crab is sold as a separate colour form with orange on the shell, and a colour name alone does not establish a species. Keep the two in separate set-ups.

Does a vampire crab need water or land?

Mainly land. The scientists who described the Javan vampire crabs found adults living on moist banks and slopes, under rocks and in dense vegetation, with juveniles near the waterline. The Fishkeeper profile recommends about two-thirds land and one-third water, with the water deep enough for the crab to submerge fully when it moults.

What temperature and water does it need?

Practical Fishkeeping and the Fishkeeper profile give 22–28°C, and OATA gives 22–27°C for crabs in the trade, so 22–27°C suits all of them. Use clean, dechlorinated fresh water; Fishkeeper gives pH 7.5–8.5 and 10–25 dH, OATA pH 7.0–8.0 and 8–18 dGH, so aim for pH 7.5–8.0 and 10–18 dGH. Keep the air humid.

How big does a Rainbow Vampire Crab get?

Small. Adult shells of the two described Javan vampire crabs measured about 1.1–1.5 cm across in the scientific description. Hobby sources give larger figures, 2–3 cm body length in Practical Fishkeeping and up to 3 cm in the Fishkeeper profile. Our crab is an unidentified trade form, so expect a crab in that range.

How many can I keep together?

Males can be territorial, so the Fishkeeper profile suggests one male with several females unless the enclosure is very spacious. Sex your crabs on arrival by the flap under the body (narrow in males, wide in females) and give each crab its own hiding place.

Can vampire crabs live with fish or shrimp?

They are best kept on their own. The Fishkeeper profile rates them as non-community and says they will hunt small fish, and the scientific description found wild crabs feeding on insects on the ground. Shrimp and small or slow fish are at risk.

Do vampire crabs breed in captivity?

Yes, they have been bred in home enclosures. The Fishkeeper profile explains that the female carries her eggs for several weeks and miniature crabs hatch directly, with no larval stage. Practical Fishkeeping reports clutches of about 50–60 young, roughly every six months. Give the young shallow water, moss and cover.

Consult the care references

• Ng, Schubart & Lukhaup (2015), Raffles Bulletin of Zoology 63: 3–13 — peer-reviewed description of two vampire crabs from central Java: habitat, behaviour, diet, colours and adult sizes.
• WoRMS: Geosesarma De Man, 1892 — the genus Geosesarma De Man, 1892 and its family, Sesarmidae.
• Practical Fishkeeping: Vampire crab, Geosesarma sp. — vampire crab feature by Chris Lukhaup: size, temperature, humidity, diet and brood size.
• Fishkeeper: Vampire Crab (Geosesarma spp.) — species profile of vampire crabs: origin, size, water values, land-to-water ratio, diet, behaviour, sexing and direct development.
• OATA: How to care for crayfish and freshwater crabs — UK trade guidance for crabs: water values, aquarium size, land area, secure lid, acclimatisation, feeding, maintenance, sexing, moulting and health checks.
• Tropical Fish Co delivery policy — current dispatch days and Live Arrival Guarantee terms.