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What Is a Fairy Shrimp?

Stephany Seipel
Stephany Seipel

Fairy shrimp are a family of approximately 300 species of small freshwater crustaceans. Most fairy shrimp live in vernal pools, which are temporary or seasonal pools that often form in grasslands. These tiny animals have short life spans, usually surviving for only three or four months, depending on how long their watery habitats last.

Most of these crustaceans are 0.5-1.5 inches (1.27-3.81 cm) long, but some species can grow as long as 3 inches (7.6 cm). The females typically are larger than the males. Fairy shrimp are able to reproduce both sexually and parthogenically, so there usually are more females than males in fairy shrimp populations.

Woman holding a book
Woman holding a book

Many species are translucent, and others are gray or blue. Some species might even be red or orange in color, depending on their diet. Most fairy shrimp subsist on algae, ciliates, protozoa and bacteria, as well as organic debris such as decaying plant or animal matter.

These upside-down swimmers have elongated bodies and 11 pairs of flattened swimming legs. Their compound eyes grow from stalks, and they have two pairs of antennae. They move by waving their front and back legs in a beating motion.

A male fairy shrimp uses a special set of clasping, pincer-like antennae to grasp the female and draw her close to him. The actual mating process takes only a few moments, but the male and female fairy shrimp usually remain attached to one another for several days. The male dies soon after mating.

The female fairy shrimp carries 10-150 viable eggs in a specialized brood sac on her abdomen. The eggs eventually fall to the soil at the bottom of the pool. Eggs that are laid during the winter often dry out when the water in the pond evaporates. Their thick shells allow them to withstand dry periods and hatch when the water reappears.

Other eggs have thin shells and hatch during the summer. The females are more likely to lay these eggs if there are a limited number of male fairy shrimp in the vernal pool. These summer eggs hatch more quickly than the winter eggs and can reach maturity in a little more than two weeks.

The juvenile fairy shrimp develop through a series of instars, or nymphal stages. They develop new segments on their bodies each time they molt, and they reach adulthood when they attain 20 segments. After maturing into adults, they mate and continue the life cycle.

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