Pelocoris femoratus

Creeping Water Bug

Pelocoris sp., Creeping Water Bug adult



Family: Naucoridae

Subfamily: Naucorinae

Length: 9.0 - 11.5


The Creeping Water Bugs are unusual in a number of ways. They seem to lack antennae, for one thing, and to lack the membranous wing area at the rear. The antennae are actually tucked into clefts under the eyes, while the hemelytra are coarser than usual and thus the membranous part appears to be lacking.

As the common name says, sometimes they creep, but they also swim. More often, they combine the two into a novel form of locomotion.

Hungerford (1920) mentioned this species eating flies and various other insects; "they will also eat snails."

Pelocoris femoratus catches prey with its enormous raptorial forelegs, and to the unwary human they can give a painful bite that "leaves a stinging, itching, burning sensation for some time, as the writer has found" (Hungerford, 1920). Hungerford also told about a collector named Beamer, whose party collected a long net full of aquatic material. Hungerford quoted Beamer's field notes, telling how as the group poked through the material they were "stung by Naucorids until a retreat was necessary."

At the University of Missouri at Columbia, the director of the entomology museum teamed up with an undergraduate research assistant and conducted a "behavior inventory" of this species (Brewer and Sites, 1994).

The two researchers collected 27 adults, then brought them into the laboratory, placing one male and one female in each of a number of glass bowls. They then recorded each behavior they observed, over a total of 62 hours of watching.

In the glass bowls they provided a concave rock for shelter (they could still see under the rock). They also used red light bulbs to watch the naucorids at night.

They found that the bugs were most active when it was dark. Among the behavior they noted were: bubble replenishment, swimming, beak stroking and other grooming, lunging toward prey, and mating.

Pelocoris, aquatic bug, dorsal view of head

Aquatic insects lack gills, and this species swims with an air bubble to supply its oxygen needs. When the oxygen runs low, the bug surfaces to replenish the air bubble. The Missouri researchers noted that Pelocoris femoratus simply lets go of the substrate and floats to the surface to secure a new bubble, while other researchers had reported the species actively swimming to the surface. The difference may lie in the shallowness of the glass bowls used in the Missouri research. In an aquarium, it seems, the bugs often do swim to the surface to replenish the air supply, as presumably they do in the wild in deeper water.

The Creeping Water Bug shown here was photographed in Upshur County, West Virginia, dipped out of a small pond. Contrary to the bug's common name, it did not creep, but swam at blazing speed in the bowl provided. The rapid swimming went on for some twenty minutes, making photography difficult. The rapid swimming may have been panic-induced, since in its normal life the bug would never have encountered such a complete lack of shelter. The bug headed quickly for shelter when it was reintroduced into the pond.

McPherson, Packauskas, and Korch (1987) studied the life history of Pelocoris femoratus in both field and laboratory.

The authors collected eighteen adults and took them to aquaria in the lab. Phantom midge larvae provided food for the adults and later for the nymphs. Eggs were laid singly, adhering to underwater plants. The eggs took an average of 18 days to hatch. From hatching through the five instars and the final molt took 63 days.

McPherson, Packauskas, and Korch concluded that Pelocoris femoratus is univoltine in their study area, and that the species overwinters as adults in the mud and muck on pond bottoms.

Map, Pelocoris femoratus

A note about our maps

Note that this is both the species page for Pelocoris femoratus and the family page for Naucoridae

American Insects site