Description

Gyrinidae are distributed worldwide with about 262 species known as of 2000. They are all aquatic. Diagnostic characters of these "whirligig beetles" include the middle and posterior legs being modified for swimming; the eyes are divided into separate upper and lower parts; the metasternum does not have an antecoxal piece, and first ventral abdominal segment is divided by the hind coxal cavities.

The larvae and adults of all species are predaceous on other insects and animals. They inhabit both quiet and slowly flowing water. Adults are usually, but not always, active during daytime, being quite gregarious, with masses of gyrating beetles very noticeable late in the season. They are conspicuous by the way they swim in tight circles on the water surface. The adults are capable of extended flight as well as of diving and swimming. Their structure is modified to produce firmness and a distinct smooth effect. The last two pairs of legs are short and flattened, bearing an outer fringe of flattened hairs, which considerably increases the area and thus gives greater swimming efficiency. During swimming and diving, the beetles carry a supply of air in a space underneath the elytra. Although valuable as natural control of mosquitoes, they have not been actively used in biological control.

The dults prey mostly on animal food although they are usually regarded as scavengers rather than predators, by feeding on various insects that fall into water. However, the larvae are exclusively predaceous, feeding on the body fluids of almost any form of animal life available in the aquatic environment that is of appropriate size.

The eggs are laid in heaps and sometimes arranged in rows on the surface of submerged foliage. Incubation is about 1.5 weeks.

Most species exit the water habitat to pupate. The pupal case that is constructed from a wide variety of resources, is made by the mature larva either on the ground or on plant stems or leaves above the surface of the water. There is usually only one generation annually in temperate climates, with overwintering being as adults. Some gyrinids retreat to mud during winter, while some remain on the water or fasten to submerged vegetation.

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References: Please refer to <biology.ref.htm>, [Additional references may be found at: MELVYL Library]

Arnett, R. H. Jr. & M. C. Thomas. 2001. American Beetles. CRC Press.

Balduf, W. V. 1935. Bionomics of Entomophagous Coleoptera. J. S. Swift Co., NY. 220 p.

Balfour-Browne, F. 1945. Ann. Mag. Nat. Hist. 21: 103-111.

Regimbart, M. 1902. Genera Insectorum, Fasc. 1. 12 p.

Romey, W. L. 1995. "Position preferences within groups: do whirligigs select positions which balance feeding opportunities with predator avoidance?". Behavioral Ecology and Sociobiology 37: 195–200.

Romey, W. L. & E. Galbraith. 2008. "Optimal group positioning after a predator attack: the influence of speed, sex, and satiation within mobile whirligig swarms". Behavioral Ecology 19: 338–343.

Romey, W. L. & D. S. Rossman. 1995. "Temperature and hunger alter grouping trade-offs in whirligig beetles". The American Midland Naturalist 134 (1): 51–62.

Romey, W. L. & A. C. Wallace. 2007. "Sex and the selfish herd: sexual segregation within nonmating whirligig groups". Behavioral Ecology 18: 910–915.