water flea Daphnia sp. Kingdom: Animalia FEATURES Phylum: Arthropoda Water fleas are compressed side to side. The body Class: Branchiopoda of these microscopic organisms is enclosed in a Order: Cladocera transparent shell that usually has a spine at the end. Four, five or six pairs of swimming legs are present. Family: Daphniidae One pair of antennae is modified for swimming and ILLINOIS STATUS helps to propel the organism through the water. The end of the female’s intestine is curled, while the end common, native of the male’s intestine is straight. Water fleas have a single, compound eye. BEHAVIORS Water fleas can be found throughout Illinois in almost any body of water. They prefer open water. These small arthropods migrate up in the water at night and down in the day, although a few live on the bottom. Water flea populations generally consist only of females in the spring and summer. Reproduction at these times is by parthenogenesis (males not required for eggs to develop). In the fall, males are produced, and they mate with the females. Fertilized eggs are deposited to “rest” on the bottom until hatching in the spring or even many years later. Water fleas eat bacteria and algae. They have a life span of several weeks. ILLINOIS RANGE © Illinois Department of Natural Resources. 2021. Biodiversity of Illinois. Unless otherwise noted, photos and images © Illinois Department of Natural Resources. © Paul Herbert female with eggs Aquatic Habitats bottomland forests; lakes, ponds and reservoirs; Lake Michigan; marshes; peatlands; rivers and streams; swamps; temporary water supplies; wet prairies and fens Woodland Habitats bottomland forests; southern Illinois lowlands Prairie and Edge Habitats none © Illinois Department of Natural Resources. 2021. Biodiversity of Illinois. Unless otherwise noted, photos and images © Illinois Department of Natural Resources..