402 INSECTS INJURIOUS TO VEGETATION. 



open and shut with the motion of the wings ; they are called the. 

 winglets^ The two balancers or poisers are short threads, knob- 

 bed at the end, and placed on each side of the hindmost part of 

 the thorax, immediately behind the winglets. The thorax is 

 often the thickest and hardest part of the body ; to it the hind- 

 body is more or less closely united, and the latter, in many fe- 

 males, ends with a tapering, retractile tube, wherewith the eggs 

 are deposited. The legs are six in number, and each of the feet 

 is provided with two claws, and two or three little cushions .or 

 skinny palms, by the help whereof the insects can walk on the 

 smoothest surfaces, and On the ceilings of rooms, with the back 

 downwards, as easily as when upright ; for the palms act hke 

 suckers, and thus prevent them from falling. 



Mosquitos and gnats are active both by day and night, but flies 

 take wing only during the day. The life of these insects, even 

 from the time when they are first hatched, is generally very short, 

 seldom lasting more than a few weeks ; but of some kinds several 

 broods are produced in the course of a single summer, and often 

 in the greatest profusion. In certain couptries and seasons they 

 multiply so fast, and appear in such immense swarms, as to be- 

 come a serious annoyance both to man and beast. 



The young insects, hatched from the eggs of gnats and of flies, 

 are .fleshy larvae, usually of a whitish color, and without legs. 

 They are commonly calldd maggots, and sometimes are mistaken 

 for worms. They vary a good deal in their forms, structure, hab- 

 its, and transformations, so that it is somewhat difficult to give any 

 general description of them. Their breathing-holes are usually 

 situated near the extremities of the body. Aquatic maggots 

 often have a tubular tail, through which they breathe, and the ori- 

 fice of this tube is sometimes surrounded with beautiful feather- 

 formed appendages. The larvae or maggots of the gnats, and of 

 nearly all those flies which have four or six bristles in the probos- 

 cis, have a distinct head covered with a horny shell. Larvae of 

 this kind, when fully grown, cast off their skins to become pupae 

 or chrysalids. These pupae ar^ usually of a brown color, and 

 somewhat resemble the chrysalids of certain moths, or more 

 nearly those of Hymenopterous insects ; for their short and imper- 

 fect legs and wings, though folded on the breast, are not immova- 



