Invertebrates
Amphipod
Amphipoda · also called amphipods, beach hoppers, sand fleas
Step near a pile of washed-up seaweed on almost any beach and you may see amphipods launch themselves into the air in a burst of tiny hops, snapping their curled bodies straight to fling themselves forward. That same basic body plan, small and flattened from side to side, turns up in nearly every aquatic and damp habitat on Earth, from mountain streams to the deepest parts of the ocean.
Overview
Amphipods, order Amphipoda, are small, laterally flattened crustaceans found in an extraordinary range of habitats worldwide, from open ocean at every depth to beaches, fresh water, and damp soil. Most scavenge or filter-feed on organic debris, and females carry developing young in a brood pouch.
Small, numerous, and everywhere
Beach-dwelling species, often called beach hoppers or sand fleas, launch themselves into the air with a sudden snap of the body. With thousands of described species occupying an enormous range of niches, amphipods form a foundational food source across countless freshwater, marine, and terrestrial food webs.
Status
Least Concern — abundant and widespread nearly everywhere water or dampness exists, with only localised pressure on beach-dwelling species from heavy coastal development or beach cleaning.
Amphipod: common questions
Why are amphipods on the beach sometimes called sand fleas?
The common names beach hopper and sand flea refer to certain amphipod species that live in the sand of ocean beaches and are capable of a sudden, flea-like hopping motion, produced by rapidly snapping their curled body straight to launch themselves into the air, though true amphipods are crustaceans and are not closely related to actual fleas, which are entirely different, blood-feeding insects.
How is an amphipod different from an isopod?
While both are small crustaceans that can look superficially similar at a glance, an amphipod's body is flattened laterally, from side to side, giving it a curved, comma-like profile, while an isopod's body is instead flattened dorsoventrally, from top to bottom, giving it a flatter, more shield-like profile, a structural difference that is one of the most reliable ways to tell the two groups apart.
Why are amphipods considered so ecologically important?
Given their enormous total abundance and extremely wide distribution across virtually every aquatic and many damp terrestrial environments, amphipods serve as a foundational food source for a huge range of larger predators, including many fish, birds, and other invertebrates, making them a critical link in numerous food webs even though individual amphipods are quite small and easily overlooked.
Do baby amphipods develop inside an egg in the water like many other crustaceans?
No, female amphipods instead carry fertilised eggs, and later the hatched young, within a specialised brood pouch located on the underside of the body, providing a degree of direct parental protection and care until the offspring have developed enough to survive independently, rather than simply releasing eggs into open water to develop entirely unprotected.