CHAPTER 8 



Megaloptera 



By H. P. Chandler 



California Department of Fish and Game 



Alderflies, Dobsonflies, Fishflies 



Adult dobsonflies (fig. 8:1a) are medium- to large- 

 sized insects with complete metamorphosis. The 

 large, broad, gray to black wings are held rooflike 

 over the body and are Similar in shape, but the hind 

 wings have a small folded area. The head is broad 

 and flat, the mouth parts are of the chewing type, 

 and the antennae are slender and multisegmented. 

 Adults may be seen making short, slightly awkward 

 flights along the margins of streams and lakes. The 

 aquatic larvae (fig. 8:16) are called hellgrammites 

 and the larger species are highly prized as fish bait. 

 They are fiercely predaceous and have strong chewing 

 mouth parts. The abdomen bears seven or eight pairs 

 of lateral gills. 



The Megaloptera are among the most primitive of 

 the winged insects, being close to the ancestral stock 

 of the Neuroptera, Mecoptera, and Hymenoptera. Almost 

 every feature of their wings can be duplicated in the 

 wings of the Paleozoic fossil insects. The branching 

 of the accessory veins from the forward side of the 

 radial sector found in several fossils can be seen in 

 Sialis. The order contains two families, Sialidae and 

 Corydalidae, with a total of about twenty genera. 

 Both families and seven genera are represented in 

 the Nearctic region. 



The adults are not aquatic and do not contact the 

 water even to deposit their eggs and thus have no 

 special need for adaptations for aquatic respiration. 

 The larvae have long, slender, tapering lateral proc- 

 esses, or tufts of filaments at the bases of these 

 processes that serve as gills. 



Key to the Families 



Adults 



1. Without ocelli; fourth tarsal segment bilobed; wing 



expanse less than 40 mm SIALIDAE 



— With 3 ocelli; fourth tarsal segment simple, not bilobed; 

 wing expanse 40 to 160 mm CORYDALIDAE 



Larvae 



1. Last abdominal segment produced as a long median 

 filament; lateral gill processes on abdominal segments 



1-7 SIALIDAE 



— Last abdominal segment without median filament, but 

 with a pair of lateral hooks; lateral filaments on 

 abdominal segments 1-8 CORYDALIDAE 



Family SIALIDAE 



Alderflies 



These slow, awkward flying, smoky to black insects 

 vary little in size, ranging from 10-15 mm. in length. 

 They are usually seen making flights along the 

 margins of streams. The larvae (fig. 8:16) are easily 

 recognized by their lateral abdominal gills, the pro- 

 longation of the last abdominal segment, and their 

 pale testaceous to white color. 



Relationships. — The adults are characterized by 

 the absence of ocelli. The head is broad, with long, 

 multisegmented antennae. The pronotum is large and 

 rectangular, two and one-half times as wide as long. 

 Sialis (fig. 8:1a), the only Nearctic genus, contains 

 about twenty species. Ross (1937) places these in 

 seven phylogenetic groups, based largely on the 

 structure of the male genitalia. The " calif ornica 

 group/' his largest, contains seven species including 

 three of the four species known from California. Three 

 groups contain but one species, one of which is S. 

 nevadensis, the fourth known California species. 



Respiration. — The larvae have five-segmented lat- 

 eral gill processes on the first seven abdominal 

 segments. The terminal process contains tracheae but 

 is not segmented. 



Life history. — The adults are probably short-lived 

 as is indicated by the soft mouth parts which appear 

 unsuited for extensive feeding. The eggs are deposited 

 in rows, forming large masses on objects overhanging 

 the water. The eggs are cylindrical, rounded at the 

 top with a curved process. They hatch during the 



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