THE SYRPHI. 373 



same genus are almost equally hurtful to other kinds 

 of grain. The well-known hopping maggot, so abun- 

 dant in rotten cheese, is the larva of another fly of 

 this tribe, the Piophila casei ; the larvse of numerous 

 species (Hydromyza, &c.) live in the mud at the 

 bottom of water, in the neighbourhood of which the 

 flies are always met with; and those of the genus 

 Tachina and its allies are for the most part parasitic 

 in the bodies of other insects, and thus assist the 

 Ichneumons in keeping their numbers in check. 



After this rapid summary of some of the principal 

 variations in the habits of the insects most nearly 

 allied to our common Fly, there are still some which 

 require a more particular mention. Hovering mo- 

 tionless in the air over the low plants in our gardens, 

 and occasionally settling for a moment upon their 

 leaves, or darting away with incredible rapidity when 

 we approach them too closely, every one must have 

 observed some elegant flies, with their bodies prettily 

 marked with yellow bands. One of the most abundant 

 of these is the Syrphus Pyrastri, a bluish-black insect 

 about half an inch in length, with perfectly trans- 

 parent wings, hairy eyes, a tawny scutellum and three 

 interrupted yellow or yellowish-white bands upon the 

 abdomen. The larva of this and of a good many other 

 species included in the same genus are remarkable 

 amongst the Diptera for their predaceous habits ; they 

 are whitish depressed maggots with pointed heads, 

 which crawl about freely upon the leaves of plants by 

 the aid of numerous small tubercular feet with which 

 their ventral surface is furnished. They feed upon the 

 Aphides, which are so common upon many plants, 

 transfixing them with a sort of trident which springs 

 from the lower part of the mouth, and then raising 



