Water Fleas

Fleas: these blood-consuming pests not only caused the devastating epidemic that occurred during the medieval period but also continue to strike fear in the hearts of people today, especially pet owners. But what about water fleas? Despite their name and resemblance to regular fleas, water fleas are actually much more different than those invasive parasites. Water fleas, also known as Cladocera, range between 0.2 - 5.0 mm in length and reside primarily in freshwater habitats. These aquatic crustaceans consist of over 600 species with the most common species being the Daphnia pulex. Despite their small size, water fleas play an important role in the aquatic ecosystem because they serve as the base of the aquatic food chain.

The anatomy of the water flea is quite fascinating. A thin protective shell called the carapace covers the majority of the organism's body. Since the shell is translucent, previously consumed foods could often be identified by the color within its abdomen. These aquatic organisms swim underwater in a hopping motion; this style of movement is caused by the large pair of antennae attached to their head, allowing them to swim in an abrupt, flea-like fashion. Below this pair of antennae is a smaller pair of antennae that functions as a sensory tool. Located within the organism’s thorax are rapidly moving thoracic limbs that are used to either gather and filter food or grasp onto its partner during mating processes. Perhaps the most interesting part of the water flea’s anatomy is the single compound eye located near the large set of antennae that occupies a huge section of the crustacean’s head. Like the small set of antennae, this fused eye has a sensory function, allowing the water flea to sense changes in light intensity to help them navigate underwater.