INDIRECT BENEFITS DERIVED FROM INSECTS. 233 



pools — the all-devouring Libellulina,^ The Asiliol^o^ which 

 are always upon the chase, seize insects with their anterior 

 legs and suck them with their haustellum. The cognate genus 

 Dioctria, particularly D. oelandica, prey upon Hymenoptera^ by 

 some unknown means, instantaneously killing the insect they 

 seize. Many species also of Empis, whose haustellum re- 

 sembles the beak of a bird, carry off in it TipularicB and other 

 small Diptera ; and, what is remarkable, you can seldom take 

 these insects in coitu, but the female has a gnat, some fly, or 

 sometimes a beetle, in her mouth. Can this be to deposit her 

 eggs in, as soon as they are impregnated by the male ? or is 

 it designed for the nuptial feast ? Even Scatophaga ster cor aria 

 and scyhalaria, and probably many others of the same tribe, 

 feed upon small flies, though their proboscis does not seem so 

 well adapted for animal as for vegetable food. 



The most unrelenting devourers of insects appear to be 

 those belonging to my fourth division, which attack them 

 under every form. These begin the work of destruction when 

 they are larvae, and continue it during the whole of their ex- 

 istence. The earwig that haunts every close place in our 

 gardens, and defiles whatever it enters, probably in some de- 

 gree makes up for its ravages by diminishing the number of 

 other insects. The cowardly and cruel Mantis, which runs 

 away from an ant, will destroy in abundance helpless flies, 

 using its anterior tibia, which with the thigh form a kind of 

 forceps, to seize its prey. The water-scorpions {Nepa, Ra- 

 natra, and Naucoris), whose fore-legs are made like those of 

 the Mantis, the water-boatman (^Notonecta), which always 

 swims upon its back, and Sigara, all live by rapine, and prey 

 upon aquatic insects. Some of this tribe are so savage that 

 they seem to love destruction for its own sake. One (^Nepa 

 cinerea) which was put into a basin of water with several 

 young tadpoles killed them all without attempting to eat one. 



Those remarkable genera of the tribe of water-bugs {Hydro- 

 coriscB Latr.), which glide over the surface of every pool with 

 such rapidity, being gifted with the faculty of walking upon 

 the water, Hydrometra, Velia^ and Gerris, subsist also upon 



1 Lesser, L. i. 2G3. note. 



