Alderflies

Definition

Aquatic megalopteran insects of the family Sialidae, characterized by soft bodies, long filamentous antennae, and two pairs of similarly sized, membranous wings with extensive net-like venation. Adults are short-lived, non-feeding, and typically found near streams and rivers where larvae develop; larvae are elongate, campodeiform predators of other aquatic invertebrates, bearing paired lateral gills on abdominal segments and a single caudal filament.

Etymology

From alder (the tree genus Alnus, common in riparian habitats where adults often rest) + fly; the common name reflects their association with waterside vegetation rather than taxonomic affinity to true flies (Diptera).

Example

Sialis lutaria, a widespread European alderfly, has larvae that burrow in silty stream bottoms and prey on chironomid larvae and oligochaete worms.

Synonyms

• Sialidae

Related Terms

• Megaloptera
• Dobsonflies
• Fishflies
• Neuropterida
• Aquatic insects
• Riparian

Usage Notes

Despite the common name, alderflies are not true flies (order Diptera) but rather neuropteroid insects with two complete wing pairs. The family Sialidae is the sole extant family of the suborder Sialodea; the closely related extinct family Euchauliodidae is known only from fossils. Alderflies are distinguished from dobsonflies and fishflies (family Corydalidae) by their smaller size, shorter mandibles, and larvae with a single terminal filament rather than paired anal prolegs with gills.