SNAKE-FLIES 57 



perfect insect ultimately emerges. The life of the 

 adult is short, being limited to a few days ; but the 

 precise duration of the complete life-history has not 

 yet been ascertained so far, at least, as the writer is 

 aware. 



The curious snake-flies 1 are easily recognizable 

 in the perfect state, because of the remarkable de- 

 velopment of the prothorax and the back of the head, 

 which together form a kind of "neck." Indeed, the 

 fore-part of the insect is very suggestive of a snake 

 whence the popular name. The female has a long, 

 slender ovipositor, and appears to lay her eggs in old 

 timber or under bark, for the larvae are found in such 

 places. They are active little creatures, which wriggle 

 rapidly backwards when alarmed, and hunt their prey 

 with the utmost voracity. Yet they are able to sustain 

 long fasts, and we may infer from this that the dura- 

 tion of the life-history depends upon the abundance or 

 scarcity of the food-supply, as is the case with some 

 other insects. " The larva of the snake-fly," says 

 Dr. Sharp, " changes to a pupa that is remarkably 

 intermediate in form between the perfect insect and 

 the larva ; the eyes, legs, wing-pads, and ovipositor 

 being but little different from those of the imago, 

 while the general form is that of the larva, and the 

 peculiar elongation of the neck of the imago is absent. 

 This pupa differs from that of Sialis in the important 

 particular that before undergoing its final ecdysis (or 

 moult) it regains its activity, and is able to run about." 

 The three or four British species of the genus Raphidia 

 frequent wooded districts, and are said to be rare, 

 though their apparent scarcity is probably due in 

 large measure to their small size and retiring habits. 



