Common Aquatic Insects in Lancaster County

I found a backswimmer in the middle of our backyard fish pond on June 13, 2014. I've seen water boatmen, whirligigs and water striders numerous times over the years, but that was the first backswimmer I ever saw. It was an exciting experience. All these water insects are well adapted and interesting in their natural habitats, but it's only the adults of each species that are seen by most people.

Backswimmers are true bugs that live in quiet water, such as ponds. They swim upside down at all levels of water, hence their common name. They use their hair-fringed, oar-like back pair of legs to push themselves through the water. For camouflage, their wings and backs are light-colored to be hard to see from below and their undersides are dark to be nearly invisible from above. They prey on land-based insects caught in the surface film, aquatic invertebrates and tadpoles. Their mouthparts inject digestive juices into their victims so they can suck out the soft body parts.

Water boatmen are also true bugs, but they swim at all depths of water right-side up, using their long, flattened middle and hind pair of legs as oars. These bugs also live in ponds, and puddles and bird baths where they feed on tiny algae suspended in the water. They are common in some ponds and grayish for camouflage against predation.

Water Strider

Water striders are another kind of true bug that lives on quiet waters and slow-moving waterways where they are often seen even by casual observers. Striders are dark on top and white below to blend into their surroundings and are also called skaters because they can walk on top of the water surface film. There they catch terrestrial insects struggling in the water, mosquito larvae and other aquatic insects that rise to the surface.       

Whirligigs are oval, shiny-black beetles about a half-inch long that live IN the surface of still water. Groups of them swim in circles (hence their name) among each other, without collision, in the surface, like so many tiny power boats. Whirligigs have unique compound eyes that see above and below the surface at the same time. They have short flat hind legs they use to swim. And they have short antennae that detect disturbances in the water's surface, to locate prey. Adult whirligigs feed on aquatic insects and invertebrates that fall onto the water's surface, perhaps giving water striders competition for food.

All these water insects are interesting to see in summer when they are active. And they are readily visible with a little searching for them. 

Photo courtesy of felixtsao