Description & Statistics

Gyrinidae are cosmopolitan in distribution but contain relatively few species (ca. 255 species known as of 1993). All gyrinids are aquatic. Important morphological characters of these "whirligig beetles" include the middle and posterior legs modified for swimming; eyes divided into separate upper and lower sections; metasternum without an antecoxal piece; first ventral abdominal segment divided by the hind coxal cavities.

All Gyrinidae are predaceous as larvae and adults. 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 a rigidity and a distinct streamlined 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.

Food.-- Adults subsist mostly if not exclusively on animal food although they are usually thought of 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 which is of suitable size.

Reproduction.-- The eggs are laid in masses, often arranged in rows, on the surface of submerged foliage. Incubation takes ca. 1-2 weeks.

Development.-- Most species leave the water to pupate. The pupal case, which is constructed from a wide variety of materials, is prepared 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 bury themselves in mud during winter, while others remain on the water or cling to submerged vegetation.

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

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.