• Expanded hind coxal plates
• Hind coxae expanded plates cover abdominal segments: 1, 2 and sometimes 3
• Legs have five segments, not including tarsal claw
• Long swimming hairs on mid and hind legs

Haliplidae, or the Crawling Water beetle, gets its name from its poor swimming abilities. Rather than swim, the beetle clings to submerged vegetation and crawls along the bottom of the stream or pond that it inhabits. This slow movement supports the idea that they are herbivores in all life stages, although it has been thought that the adults were partially carnivorous. Haliplidae diet preferences are varied based on species. For example, diets can range from a mixture of chironomid eggs, oligochaet worms and small crustaceans, to hydrozoans, algae, characeans and seed-baring plants (3).

Found most commonly in temperate regions (1).They can be seen in calm waters, the adults, larvae, and pupae are found within the same habitat. When threatened at all, they immediately dive straight down, and cling and burrow on the water bottom. Most Haliplidae prefer standing water such as large ponds or slow moving freshwater streams with no shade and high algal growth (1).The Crawling Water beetle can be used to control water plants that have become pests. Agasicles hygrophila, an alticine Chrysomelidae, was introduced into the USA from South America to control Alligatorweed (Altexrnanthera) (4).

The adults range in size from 2.5-4.5mm, and have beautiful spotted shells with uniform rows of black punctures. Their colors range from brown/orange, to yellow/green. Their backs are boat shaped, coming to a point at the rear, and are extremely convex. An easily identifiable feature of this beetle is its ventral view. All Crawling Water beetles possess the characteristic of a flattened sternal ridge, running from the prosternum down to the abdomen. And, they have the fairly uncommon feature of metacoxal plates that cover their basal segments, and the first 2 segments of their legs. The abdomen is comepletely shielded by these features. These plates assist adults in storeing oxygen obtained at the surface in three places; under the wings, at the tail, and under the large coxal plates. This allows the beetle to breathe underwater for extended periods of time (2). They also have protruding eyes and filiform antennae with 11 segments, and their basal antennae are unusually short. Unlike most water beetles, the haliplids are able to remain active through the winter. They congregate in deep water among aquatic plants and where air bubbles collect under the ice (1).

The larvae of this beetle vary widely in appearance, with some species having many spine-tipped filaments radiating from the body, giving it the appearance of a small water porcupine. Other species have no filaments at all. All larvae have some form of forks or teeth on their legs or basal abdominal segment.

• Video: Peltodytes sp. swimming

(1) Hickman, J. R. 1931. Contribution to the biology of the Haliplidae (Coleoptera).Ann. Ent. Soc. Am. 24:129-142.

(2) Arnett, R.H., Jr., and M.C. Thomas. (eds.). 2000. American Beetles. Volume 1. Archostemmata, Myxophaga, Adephaga, Polyphaga: Staphyliniformia. CRC Press LLC, Boca Raton, FL. xvi + 443 pp.

(3) Seeger, W. 1971a. Autökologische Untersuchungen an Halipliden mit zoogeographischen Anmerkungen. Archiv für Hydrobiologie

(4) Mogi, M., Sunahara, T. & Selomo, M. (1999) Mosquito and aquatic predator communities in ground pools on lands deforested for rice field development in Central Sulawesi, Indonesia. Journal of the American Mosquito Control Association 15 (2): 92-97.

Merritt, R W., K W. Cummins, and M B. Berg. An Introduction to the Aquatic Insects of North America. Dubuque, Iowa: Kendall/Hunt Company, 2008