The Alderflies of Florida

Although the North American forms of this family are probably the richest fauna in the world with 23 species, only one of these has been recorded from Florida (Tarter et al., 1978). To date, only eight adult specimens have been collected in North Florida and the Panhandle. These were determined recently by M. F. Whiting and represent three species of Sialis. The biology and habits of the species have been treated in detail by Davis (1903) and Evans (1978). These insects are considered beneficial.

Adults are moderately large insects (11-14 mm) with dark brown bodies and brown suffused wings (Fig. 1). They move fairly rapidly and are mostly diurnal. Adult life span is probably short since the soft mouthparts do not seem fitted for extensive feeding. The eggs are laid in rows–forming large masses situated on branches, bridges, and other objects overhanging the water. The eggs are cylindrical with a distinct apical curled tassel. The larvae live in water and are predaceous, hunting mostly caddisflies under stones and other habitats. There are as many as 10 larval instars, and the larval stage lasts up to 2 or more years. When mature, the larva crawls out of the water and digs into the bank to form an earthen cell several feet from the edge of the water. Larval respiration occurs through 7 pairs of tracheal filaments located laterally on the abdomen. These filaments along with the caudal filament make the larva (Fig. 2) distinctive among all aquatic larvae.

Adults are extremely archaic insects with the wing venation nearly unchanged since the Permian (200+ million years ago). Adams (1958) stated that no other living insect group shares so many wing features with the Protoperlaria, a fossil order considered ancestral to the Plecoptera. The bilobed fourth tarsomere together with a hypognathous head and broad base of the hindwing are diagnostic adult characters.