Isopods

Do you love looking for crustaceans but hate getting wet and salty in the ocean? Well have I got the organism for you. Pill bugs (also known as rolly-pollies) and their cousins the sow bugs and wood lice are all actually crustaceans and not insects in the family collectively known as isopods (pod or stem foot). Pill bugs are unique for their armadillo-like ability to roll up into a ball when startled (pictured above).

Crustaceans are an incredibly diverse subfamily of the arthropod family (animals with exoskeletons) that differ from others like insects and spiders in their highly modified legs. Most insects and spiders have very similar leg structure to one another but crustaceans often have modified legs that end in claws, paddle-like structures for swimming, or even extra pairs of antennae for smelling and other sensory functions.

Besides the ubiquitous pill bugs and wood lice the isopod family contains some pretty weird creatures. The deep-sea dwelling Bathynomus giganteus can grow to sizes of nearly 2.5 feet and is one of the main denizens of whale falls (whale carcasses that have fallen to the bottom of the ocean). Several parasitic isopods have evolved to a particularly bizarre niche: they replace the tongue of a fish. By sucking the blood from the tongue until it atrophies and becomes useless they will take its place. Most of these isopods then feed off of either blood or mucus produced by the fish. But hey, at least the fish are usually able to use the isopod just as they used their real tongue!

There are a few other families of terrestrial crustaceans. The others are all true crabs or hermit crabs including the coconut crab which is the largest hermit crab (and largest terrestrial arthropod) and the only one (to my knowledge) that does not protect itself with a gastropod shell or some other kind of housing.