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Today on Animal Fact Files we’re discussing amphipods. These animals have many other common names: lawn shrimp, scuds, sideswimmers, sand fleas, landhoppers– the list goes on. With thousands of described species living around the world in just about every moist habitat that exists, it's no wonder they've gained a number of names. Let's be clear, however, that amphipods are not shrimp. These arthropods are crustaceans, but they're more closely related to isopods than decapods. The name "amphipod" means "different feet" and clearly delineates them from their isopod relatives, the "equal feet" arthropods. All of an isopod's legs are equal, while an amphipod has two different types of legs: some for walking, in the front, and some for swimming, in the back.

Some amphipods are so abundant they're sometimes referred to as the "insects of the ocean" however, these animals are not insects and they're not exclusively ocean-dwelling. While there are species found from beach sand to the ocean depths, amphipods also inhabit freshwater lakes, streams, rivers, and more, as well as terrestrial places such as soggy moss or rotting leaves. In fact, they're detritus consumers and regularly help with the breakdown of organic waste, both plant and animal. They also eat algae. In turn, amphipods provide nutrition to many larger animal species such as ducks and other waterfowl, fish, aquatic mammals, crustaceans, and many more!

Amphipods range in color from pink to green and can even appear translucent. They're generally small, reaching less than half an inch (13 mm) long, however, the largest species (Alicella gigantea) has been documented at over a foot (30 cm) in length! These animals are laterally compressed, so they're taller than they are wide. If they have eyes, these are non-moving and not stalked like a snail's eyes, and the males have larger, grabbing claws at the end of their walking legs to help grasp the female during mating.

Amphipods are direct developers with small, adult-shaped babies hatching from their eggs. Fertilization is believed to occur externally and the female possesses a brood sac along her bottom in which the eggs will remain and develop. It takes about one to three weeks for the eggs to hatch, however, the young remain with their mother until she next molts, at which point they babies are shed and go their separate ways. In general, the entire process from egg to reproductive adult takes less than a year.

Terrestrial amphipods are sometimes seen in large numbers after heavy rain. They migrate from the soaked soil to drier places such as concrete patios or even under doors and into human dwellings. Unfortunately for the amphipods, they're ill-equipped for retaining moisture, they don't have a cuticle, so they easily desiccate if left without water for too long. It's not uncommon to see them die in large numbers right around the base of exterior doorways. When they die, these animals often appear dark red or brown. Although amphipods can't fly, they have multiple methods for moving around on land. They can hop which is also how they get the common name "flea". They'll also opportunistically hitch rides in bird feathers. This is believed to be part of why they have such a wide-ranging distribution!

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