Vampire Crab
Geosesarma dennerle
A purple-and-orange semi-terrestrial crab that needs a paludarium, not a fish tank - and no salt water at any stage.
| Difficulty | Intermediate |
| Min. Tank Size | 40 L |
| Temperature | 24.0–28.0 °C |
| pH Range | 7.0–8.0 |
| Max Size | 5.0 cm |
| Lifespan | 2-3 years |
| Diet | Omnivore |
| Temperament | Semi-aggressive |
Quick answer
The vampire crab (Geosesarma dennerle) is a semi-terrestrial freshwater crab that needs a paludarium, not an aquarium. It requires a land area covering at least half the floor space, shallow fresh water at 24-28 C and pH 7.0-8.0, high humidity, a secure lid, and it reaches about 5 cm across the legs. It does not need salt water at any stage, unlike most other ornamental crabs.
Do vampire crabs need salt water?
No. This is the most frequently asked question about the species and the answer is unambiguous: Geosesarma is one of the very few crab genera that completes its entire life cycle in fresh water. Females carry a small number of eggs and release fully formed miniature crabs rather than planktonic larvae, so there is no marine stage to accommodate.
This matters because most crabs sold in Australian shops - fiddler crabs, red claw crabs, thai devil crabs - are brackish or marine animals, and generic crab advice will tell you to add marine salt. Doing that to a vampire crab is harmful. Use dechlorinated fresh water only.
Vampire crab water parameters
| Parameter | Target | Notes |
|---|---|---|
| Temperature | 24-28 C | Air temperature matters as much as water temperature. Heat the enclosure, not just the pool. |
| pH | 7.0-8.0 | Neutral to slightly alkaline. Most Australian tap water sits in this range without adjustment. |
| GH | 8-15 dGH | Moderately hard. Calcium is needed for shell development after each moult. |
| KH | 4-10 dKH | Enough buffering to keep pH steady between water changes. |
| Humidity | 75-85% | The single most important and most commonly neglected parameter. |
| Water depth | 3-8 cm | Shallow. These are poor swimmers and can drown in deep water with no exit. |
Water quality still matters despite the small volume - a shallow pool fouls quickly. Change 30-50% of the water weekly, which on a typical setup is only a few litres.
Setting up a vampire crab paludarium
The commonest way to kill a vampire crab is to house it in a standard aquarium filled with water. They are semi-terrestrial: in the wild they live in humid forest leaf litter near streams, entering water to feed and moisten their gills but spending most of their time on land. A crab with no way out of the water will exhaust itself and drown.
Enclosure
A 60 × 30 cm footprint suits a small group of three to five. Vertical space matters less than floor area, but you need a tightly fitting lid - vampire crabs climb silicone, cables and heater cords, and a determined escapee will be found dry behind a bookshelf.
Land and water split
Aim for at least 50% land, and 60-70% is better. Build the land section with a coco fibre and sphagnum substrate 5-8 cm deep so the crabs can burrow, then slope it down to a shallow pool. Cork bark, driftwood, leaf litter and dense planting on the land side give the cover they need to feel secure enough to be visible.
Heating and humidity
A low-wattage heat mat on the back or side of the enclosure, controlled by a thermostat, holds air temperature more reliably than a submersible heater in a shallow pool. Mist daily. In a dry Australian summer, or in an air-conditioned room, humidity is the parameter most likely to fall out of range without you noticing - fit a hygrometer.
Planting
Pothos, java moss, cryptocorynes grown emersed, ferns and bromeliads all work well and help hold humidity. Vampire crabs will nibble soft foliage but rarely destroy established planting.
Diet
Omnivorous and unfussy. A varied diet keeps colour strong and moults clean:
- Sinking shrimp and crab pellets as a staple
- Bloodworm, brine shrimp and the occasional piece of raw prawn for protein
- Blanched spinach, zucchini, carrot and dried leaf litter
- A cuttlebone or calcium block left in the enclosure permanently - calcium availability is the difference between a clean moult and a fatal one
Feed small amounts every second day and remove uneaten food, since the enclosed, humid environment grows mould quickly.
Moulting
Moulting is the riskiest event in a vampire crab's life. The crab will bury itself and become inactive for several days beforehand, then emerge pale and soft. During this period it is defenceless and other crabs will attack it, so multiple hides and adequate floor space are not optional in a group.
Leave the shed exoskeleton in the enclosure. The crab will eat it to recover calcium. A discarded shell is regularly mistaken for a dead crab - check for a hollow shell with a split at the back before assuming the worst.
Behaviour, groups and tank mates
Vampire crabs are social enough to be kept in groups and territorial enough that space matters. A ratio of one male to two or three females reduces conflict, since males will fight persistently in close quarters. Provide more hides than crabs.
They are not compatible with fish in any meaningful sense - the water is too shallow, and any small fish sharing the pool is food. Do not mix them with other crab species. Snails are generally left alone. Treat this as a species enclosure.
Are vampire crabs legal in Australia?
Geosesarma species are available through Australian aquarium retailers and specialist invertebrate keepers. As with all ornamental aquatic species, import and keeping regulations differ between states and change over time - check current requirements with your state fisheries authority before purchasing, and buy from an established Australian retailer rather than importing.
Common vampire crab species
| Species | Appearance | Notes |
|---|---|---|
| Geosesarma dennerle | Purple body, cream-yellow claws, yellow eyes | The standard "vampire crab" of the trade and the most widely available. |
| Geosesarma hagen | Deep red to maroon body, orange claws | Often sold as "red devil crab". Identical care requirements. |
| Geosesarma notophorum | Orange-brown, paler claws | Slightly larger. Same paludarium needs. |
Trade names are applied loosely and the same species is sold under several. Care requirements across the genus are close enough that this rarely matters in practice.
Breeding
Straightforward in a well-maintained group, which is a large part of the appeal. Females carry 20-40 eggs beneath the abdomen for around four weeks and release fully formed juveniles roughly 2 mm across - there is no larval stage requiring salt water or special rearing.
Juveniles need dense leaf litter and moss to hide in, and will be eaten by adults if cover is inadequate. They take powdered shrimp food and biofilm from the leaf litter. Expect them to reach adult size in six to eight months.
Health and common problems
Failed moults are the leading cause of death and almost always trace back to insufficient calcium or humidity that has been allowed to drop. Drowning follows, in enclosures where the land area is too small or the exit from the water too steep. Escape is third - check the lid seal around every cable entry. Genuine disease is rare; almost all losses are husbandry.
Never use copper-based medications anywhere near them, and be careful with plant fertilisers containing copper.
Is a vampire crab right for you?
Yes, if you want a striking, active, genuinely interesting invertebrate and are willing to build and maintain a paludarium. They are hardy once housed correctly, breed readily, and are far more visible than most nocturnal invertebrates.
No, if you want something for an existing community aquarium. There is no version of this animal that works in a standard fish tank, and the majority of vampire crabs sold in Australia die because that is exactly where they are put.
How to Tell Males from Females
Sexual dimorphism is limited. Females tend to be fuller-bodied when in breeding condition and males slightly slimmer or more intensely coloured, but reliable sexing generally requires mature fish observed side by side, or spawning behaviour.
