Yes. Vampire crabs can climb out of an open-top enclosure, and an open top lets out the humid air they live in, so every vampire crab tank needs a lid that closes all the way round. If you’ve got a rimless or open-top aquascape, you don’t need a new tank. You need a cover cut to fit it.

Below: why tall glass and a low water line don’t do the lid’s job, what happens to a crab that gets out, and how to close an open top without sealing the tank like a jar.

Why vampire crabs climb out of an open-top tank

Vampire crabs climb, and an open top leaves them a way out from anything that reaches the rim. They’re semi-terrestrial crabs that spend their time on land and go down into the water, so even a tank with a low water line gives them plenty to walk up.

Climbing is part of how some of these crabs live. In the wild, G. bunian in northern Malaysia was collected at night in burrows and on a low shrub about 1.5 m (5 ft) off the ground, and the scientists who described it think it probably lives partly in the vegetation.¹ At home, one keeper reports that once the lights go out, their crabs are often up on the waterfall or climbing about on the back and side walls.

So what counts as a way out? In practice, anything that touches the rim. Treat each of these as a ladder:

Airline and filter tubing running over the edge.
Heater and light cords.
A filter hanging on the glass.
Wood or rock leaning against the top edge.
Plants and moss growing up to the rim or over it.

Can a tall tank with a low water line replace the lid?

No. Height only helps until a crab finds a cord, a tube or a stem, and a working paludarium is full of them: the heater cable, the filter, moss on the wood, plants climbing the back. You’d have to strip out everything the crabs need just to keep the walls bare.

A tall, open tank also doesn’t fix the other problem, which is dry air. We wouldn’t trust height alone for a single night.

What happens to a vampire crab that gets out of the tank?

It starts drying out, so a crab loose in the room needs finding fast. Land crabs lose most of their water through the shell and the gills, and when crabs and other crustaceans dry out, their gill surfaces collapse and take up less oxygen.² That finding covers land crabs in general and wasn’t measured on vampire crabs, but it’s why a missing crab is urgent. A missing vampire crab isn’t always loose in the room.

Before you search the room, though, look in the water section, because vampire crabs usually go into the water to molt and a molting crab can stay out of sight there. Then check the lid gap by gap, using the checks in vampire crab tank setup, and search the floor around the tank.

Why an open-top vampire crab tank can’t stay humid

The lid is what keeps the humidity in, so an open top keeps losing the damp air your crabs live in. Dry air is how vampire crab tanks usually fail, and the fix is a closed lid, moist substrate and moss, and regular misting. Get the humidity, the lid and the water section right and the rest of vampire crab care is fine tuning.

With the lid closed, keepers mist about once a day, more often while new moss and plants settle in. With the top open, you’d be chasing dry air all day. Moss goes brown where it dries out. Keep the lid closed between mistings to help the vampire crab tank stay humid.

How to close an open-top or rimless tank for vampire crabs

Fit a cover that sits over the whole top of the tank, then close the gaps it leaves around cords and tubing. You don’t need anything special, just something that covers the whole top and stays put.

Measure the outside edge of the tank and have glass or clear acrylic cut to sit on it, or use a fine mesh lid made to fit. If you pick mesh, check it against your smallest crab, because newly hatched crablets are far smaller than adults.
Cut one small notch at the back for cords and tubing, and pack it with aquarium foam or sponge so nothing is left open around them.
Leave a little ventilation, such as a small screened vent. Mould is common in closed vampire crab tanks, especially in the first weeks. If it keeps coming back, give the tank a bit more air rather than taking the lid off.
Trim plants and lower any wood or rock so nothing touches the cover or props up a corner.
Make closing the lid the last thing you do after every feeding and misting.

Fit the cover and run the tank with it closed for a few days before you order, so you can see it holds humidity and sits flat. Our tank-bred vampire crabs go into that finished tank. Everything in our catalog is bred or propagated in our own tanks rather than collected from the wild.