FAMILIES OF MEGALOPTERA OF BRITISH COLUMBIA

 

by

R. A. Cannings and G. G. E. Scudder 

Copyright © 2007 - All rights reserved

Key to families

1.	Head with 3 ocelli; fourth tarsal segment cylindrical	Corydalidae
-	Head without ocelli; fourth tarsal segment bilobed	Sialidae

Description of Families

Family Corydalidae (Dobsonflies or Fishflies) (Fig. 1)

Large insects with wing span usually greater than 45 mm, but often up to over 140 mm. Generally grey or blackish in colour with mottled or banded wings. Head with three ocelli, and mandibles sometimes sexually dimorphic. Antennae filiform, moniliform or pectinate, and submentum and gula Y-shaped. Legs with unmodified, cylindrical fourth tarsal segment on each.

Adults are usually crepuscular, and often attracted to light. The ovoid eggs with prominent, knobbed micropy (or projection), are laid in masses on objects near water. Egg masses may be one to five layered, and with 300 to 3000 eggs. Larvae are aquatic and aggressively predaceous.

Western species have larvae that live on the bottom of fast flowing steams. They characteristically have eight pairs of lateral abdominal projections that function as gills, and the abdomen ends in a pair of two strong hooks. Evidently, most species take two to five years to complete the life cycle.

Worldwide there are some 16 genera with about 200 mostly temperate species. Seven genera and 19 species occur in North America, with five genera and five species in two subfamilies known from Canada.

The only representation of the Corydalinae, Corydalus cornutus (Linnaeus) in Canada is restricted to Quebec, and is easily recognized by the size (wing span 140 mm) and sexual dimorphism, with male possessing elongate, sickle-shaped and tusk-like mandibles that are about 40 mm long. Such males have been seen to “dual” with each other, and to prod the female during courtship. The larvae, commonly called “hellgrammites” feed on invertebrates, small fish, and amphibia, and are often used as fish bait.

Four genera in the subfamily Chauliodinae, each with a single species, occur in Canada. Nigronia serricornis (Say) occurs in Manitoba and Saskatchewan, is 20 to 30 mm long, with serrate antennae, and wings blackish with white markings. The species is uncommon, and larvae live in stagnant water. Chauliodes pecticornis (Linnaeus), Dysmicohermes disjunctus (Walker) and Protochauliodes spenceri Munroe in Canada are confined to British Columbia.

Chauliodes pecticornis, reported so far only from Cloverdale and Cowichan, is a greyish, mottled species with characteristic pectinate antennae. The widely distributed Dysmicohermes disjunctus, recorded from Vancouver Island, the lower mainland, as well as Bella Coola, Ocean Falls, Oliver and Kaslo, is 50 to 60 mm long, and has the mesothorax and metathorax densely clothed with curly setae, which appear almost woolly. The gena are angulate, and the mandibles are prominent, while the forewings have dark blotches on the costal and subcostal veins. Protochauliodes spenceri is mostly found on southern Vancouver Island, although there have been specimens collected at Cultus Lake. Adults are 30 to 35 mm long, with the mesothorax and metathorax at most with sparse, fine, grey setae. The gena are smoothly rounded, the mandibles are not prominent, and the forewings are at most spotted on the costa and subcosta. All three species also have distinctive wing venation, but the differences are not easy to detect. Chauliodes pecticornis and Protochauliodes spenceri are considered to be rare in the province.

Family Sialidae (Alderflies) (Fig. 2)

Medium-sized insects, 10 to 15 mm long. Rather uniform in appearance, smoky to black in colour. The head with chewing mouthparts, may have orange to black markings, but lacks ocelli. The antennae are filiform to moniliform, and the submentum and gula are parallel-sided. The legs have the fourth segment of the tarsus bilobed.

Adults are diurnal, and have a slow and awkward flight. They rarely occur more than a few metres from water, and can often be found resting on alders near streams. Courtship involves communication by abdominal drumming in some species.

Eggs are laid in rows or masses on objects near water. The aquatic larvae are predaceous bottom-dwellers, and have been found burrowing into the mud and detritus of lake or stream bottoms, particularly where the floor is covered with vegetation, such as Phragmites. They feed on aquatic arthropods, and characteristically have seven pairs of segmented lateral appendages, and an abdomen terminating in a long median process tapering to a fine point. There are no anal prolegs or abdominal tufts of gills. The life cycle is typically one or two years.

Worldwide there are four genera and 50 to 60 species. The Sialidae is a cosmopolitan taxon, well represented in the Holarctic and the Australian region. The only genus present in North America is the Holarctic Sialis, with 24 species reported from the Nearctic. Twelve of these species occur in Canada, with six known from British Columbia. Species are very difficult to tell part, and identification depends on characters in the male genitalia.

The commonest and most widely distributed species in British Columbia is Sialis rotunda Banks, recorded from southern Vancouver Island, the lower mainland, and the Okanagan. Sialis californica Banks is less common, but occurs in the same areas. Sialis veleta Ross also occurs in the Okanagan Valley, having been collected at Osoyoos, Penticton and Salmon Arm, but it is also know from the Petitot River on the Liard Highway. The other three species in the province are quite rare. Sialis hamata Ross has only been recorded from Creston, and S. joppa Ross is known from only Cowichan Lake and Vernon. Sialis concava Banks also occurs in British Columbia, but the precise location is not recorded

 

Note:

This write up is extracted from the forthcoming publication by Scudder and Cannings:  The Insect Families of British Columbia.
Illustrations by L. L. Lucas.  Copyright © 2005 - All rights reserved