INDIRECT BENEFITS DERIVED FROM INSECTS. 193 



abundance helpless flies, using its anterior tibia, which with the thigh form 

 a kind of forceps, to s,eize 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 (^Nepn 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 (Hydrocorisce 

 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 aquatic insects. A large number of 

 the land-bugs (Geocorisa Latr.) plunge their rostrum into the larvae of 

 Lepidoptera, and suck the contents of their bodies ; and Reduvius per- 

 sonatus, which ought on that account to be encouraged, is particularly 

 fond of the bed-bug, as, according to Kuhn, is Pentatoma bidens, six or 

 eight of which, shut up in a room swarming with the bed-bug, for several 

 weeks, completely extirpated the latter.' 



But of all the insects that are locomotive and pursue their prey in every 

 state, none are greater enemies of their fellow tribes tban the Libellulina, 

 and none are provided with more powerful and singular instruments of 

 assault. In the larva and pupa states, during which they live in the 

 water and prey upon aquatic insects, they are furnished with two pair of 

 strong jaws, covered by a kind of mask armed with a pair of forceps or 

 claws, which the animal has the power of pushing from it to catch any 

 thing at a distance.^ When an aquatic insect passes within its reach, it 

 suddenly darts forth the mask, opens the forceps, seizes the unfortunate 

 victim, and brings it within the action of its jaws. 



When they assume the imago state, their habits do not, like those of 

 the white ants, become more mild and gentle, but, on the contrary, are 

 more sanguinary and rapacious than ever ; so that the name given to 

 them in England, " Dragon-flies," seems much more applicable than 

 " Demoiselles," by which the French distinguish them. Their motions, 

 it is true, are light and airy ; their dress is silky, brilliant, and variegated, 

 and trimmed with the finest lace : so far the resemblance holds ; but their 

 purpose, except at the time of love, is always destruction, in which surely 

 they have no resemblance to the ladies. I have been much amused by 

 observing the proceedings of a species not uncommon here, Anex Impe- 

 rator of Dr. Leach. It keeps wheeling round and round, and backwards 

 and forwards, over a considerable portion of the pool it frequents. If 

 one of the same species comes in its way, a battle ensues ; if other species 

 of Lihellulina presume to approach, it drives them away, and it is con- 

 tinually engaged in catching case-worm flies and other insects (for the 

 species of this tribe all catch their prey when on the wing, and their large 

 eyes seem given them to enable them the more readily to do this.) that 

 flyover the water, pulling off their wings with great adroitness and devour- 

 ing in an instant the contents of the body. From the number of insects 

 of this tribe which are every where to be observed, we may conjecture 



' Naturforschcr, St. 6. aad Fallen, Hemipt. Suec. 142. quoted by Westwood, MoJ. Class, of 

 Ins. ii. 486. 

 « Reaum. vi. 400. t. 36—38. 



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