Harmless to people, and you will never meet one — it lives on the deep sea floor. It is a scavenger with no venom and no interest in anything living that is larger than it.
SizeCommonly 19–36 cm; the largest recorded approach 50 cm
MarkingsEnormous for an isopod — up to about 50 cm, against 18 mm for a garden pill bug · Pale lilac to grey, with the same overlapping armoured plates as a woodlouse
WhereCold, dark, high-pressure water on the deep ocean floor.
How to tell it apart
Enormous for an isopod — up to about 50 cm, against 18 mm for a garden pill bug
Pale lilac to grey, with the same overlapping armoured plates as a woodlouse
Large fixed compound eyes set wide apart on the head
Seven pairs of legs and the ability to roll up, exactly like its land relatives
Found only in deep water, typically 150–2,000 m down
Where you’ll find it
The deep Atlantic, including the Gulf of Mexico and the Caribbean, with related Bathynomus species in the Pacific and Indian oceans.
Cold, dark, high-pressure water on the deep ocean floor.
How it behaves
It is a scavenger, and its biology is shaped by how rarely food arrives. It gorges when a carcass reaches the sea floor and can then go a very long time without eating — one kept in a Japanese aquarium famously refused food for years. Deep-sea gigantism, the tendency for cold high-pressure water to produce oversized versions of small animals, is the usual explanation for the size, though it is not fully settled.
You’ve found one indoors
Nothing you could do. If you are here because you searched for isopods and got this, the animal you are actually looking at is almost certainly a woodlouse or a pill bug in the garden — same order, a thousandth of the size, equally harmless.
Common questions
Is a giant isopod related to a woodlouse?
Directly. Both are isopod crustaceans with the same body plan — segmented armour, seven pairs of legs, and the ability to roll up. One lives under a log and one lives two kilometres down.
Can you keep one?
Not realistically. They need cold, dark, high-pressure conditions that only a handful of research aquariums can provide.
Do they bite?
They can grip and scavenge, but they are not a threat to people and are not encountered outside deep-water trawls and submersibles.
Tom Kennedy · CC-BY