Dobsons 



13 



I. Sialididce — These are the dobsons, the fish flies 

 and the orl flies. The largest is Corydalis, the common 

 dobson (fig. 120), whose larva is the well known "hell- 

 grammite", that is widely 

 used as bait for bass. It 

 lives under stones in 

 rapids. It is a "crawler" 

 of forbidding appearance, 

 two or three inches long 

 when grown, having a 

 stout, greenish black body, 

 sprawling, hairy legs, and 

 paired fleshy lateral pro- 

 cesses at the sides of the 

 abdomen. There is a 

 minute tuft of soft white 

 gills under the base of each 

 lateral process. There is 

 a pair of stout fleshy pro- 

 legs at the end of the ab- 

 domen, each one armed 

 with a pair of grappling 

 hooks. The larvae of the 

 fish-flies (Chauliodes) are 

 similar in form, but smaller 

 and lack the gill tufts under 



the lateral filaments. The larva of the orl-fly differs 

 conspicuously in having no prolegs or hooks at the end 

 of the body, but instead, a long tapering slender 

 tail. Fish-fly larvae are most commonly found clinging 

 to submerged logs and timbers. Orl-fly larvae burrow 

 in the sandy beds of pools in streams and in lake shores. 

 All appear to be carnivorous, but little is known of 

 the feeding habits of either larvae or adults. Tho large 

 and conspicuous insects they are rather secretive and 

 are rarely abundant, and they have b ;en little observed. 



Fig. 120. An adult female dob- 

 son, Corydalis cornuta, natural 



