The water flea is a microscopic crustacean that gets its nickname from the jerky, flea-like motions it makes while swimming. A member of the genus daphnia and the order Cladocera, the crustacean is only distantly related to land-based fleas. More than 600 species have been described and cataloged as of 2011, and many more species are expected to be identified.
The body structure of the crustacean, an arthropod, is like that of other insects in that it is divided into segments. These separate areas are difficult to detect in most species of water flea, however, because the segments tend to be almost or totally fused together. Like other insects, this organism has an exoskeleton and from three to six pairs of legs. They have compound eyes and antennae. Their head is usually bent down toward the rest of their body, a division typically indicated by a small notch or groove.
Water fleas live in various aquatic environments, such as rivers, ponds, freshwater lakes and streams. Some species live in swamps that are acidic. They are, however, mainly freshwater dwellers.
Various species have different lifecycles and lifespans. Their longevity often depends on the temperature of their aquatic environment. Average lifespans for different daphnia species range from 29 days to 108 days, with the maximum lifespan being no more than about a year.
The feeding habits of the water flea are similar to those of many aquatic creatures. Depending on their species and location, they eat multiple small organisms such as miniscule crustaceans and rotifers, and organic particles and creatures such as algae from the water in which they dwell. The crustacean is a filter feeder that consumes organic debris such as bacteria that float in water. They also consume organic material found on the bottom of lakes and streams. As part of the aquatic circle of life, fish and frogs often feed on water fleas.
Most water fleas are asexual and reproduce by parthenogenesis, which means embryonic growth and fertilization occur without requiring fertilization from a male. In some species and under certain conditions, males — which are considerably smaller than females — are required to fertilize eggs. This is, however, the exception. While some species are plentiful, others are endangered. The stability of a particular population depends on the conditions of the location in which the species resides.