Beetles

Hydrophilidae.

Adults of this family are omnivorous scavengers of organic detritus in ponds, lakes, marshes, and streams. Their food is principally of plant origin, but they occasionally eat dead animals. They are distinguished from their most similar aquatic relatives, the predaceous water beetles (Dytiscidae), by their prominent maxillary palps that are longer than the antennae. The antennae are short and clubbed and the hind legs flattened, with a fringe of hairs. Most are dark brown or black, rarely patterned. The body is strongly convex, and the thorax of some possesses a mid-ventral keel, which projects posteriorly as a sharp, free spine. They are poorer swimmers than dytiscids and move their legs alternately, as in walking. They also appear silvery beneath from a thin layer of air held there by a thick pile. Air is captured at the surface, head up, with the help of the antennae and tapped with thoracic spiracles.

The larval feeding habits, in contrast to those of the adult, are strictly predaceous. They are voracious pursuers of other aquatic invertebrates, including small vertebrates, such as fish and tadpoles. Varied in form, they mostly lack abdominal appendages and have short or toothed mandibles.

The most conspicuous of the 360 Neotropical species belong to the genera Hydrophilus (fig. 9.3f), Tropisternus (fig. 9.3d), and Berosus (fig. 9.3e). Species in

Hydrophilus are much larger than the others (BL 40-50 mm) and are occasionally noticed around electric lights near bodies of water. The biology and literature pertaining to the family in Latin America are reviewed by Bachmann (1977) and Span-gler (1981, 1982).

References

Bachmann, A. O. 1977. Hydraenidae y Hydrophilidae. In S. H. Hurlbert, ed., Biota acuática de sudamérica austral. San Diego State Univ., San Diego. Pp. 231-237. Spangler, P. J. 1981. Hydrophilidae. In S. H. Hurlbert, G. Rodriguez, and N. Dias dos Santos, eds., Aquatic biota of tropical South America. Pt. 1. Arthropoda. San Diego State Univ., San Diego. Pp. 163-175. Spangler, P. J. 1982. Hydrophilidae. In S. H. Hurlbert and A. Villalobos Figueroa, eds., Aquatic biota of Mexico, Central America and the West Indies. San Diego State Univ., San Diego. Pp. 355-363.

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