170 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



matter, in fresh water, etc., and from them hatch larvae, usually 

 called grubs, with three pairs of legs (sometimes wanting), 

 biting mouth-parts, simple eyes and small antennae. These 

 larvae may be predaceous, as water-tigers (larvae of water- 

 beetles), or plant feeders, as the larvae of the long-horn and 

 leaf-beetles, or carrion feeders, as those of the burying beetles 

 and so on. They grow, molt several times, and finally change 

 into a pupa either on or in the food, or very often in a rough 

 cell underground. From the pupa issues the fully developed 

 winged beetle, which usually has the same food habits as the 

 larva. 



The economic status of the order Coleoptera is an important 

 one. So many of the beetles are plant feeders and are such 

 voracious eaters in both larval and adult stages that the order 

 must be held to be one of the most destructive in the insect 

 class. Such injurious pests as the Colorado potato-beetle, the 

 round-headed and flat-headed appletree borers, the wire-worms 

 (larvae of click-beetles), the white grubs of meadows and lawns 

 (larvae of June-beetles), the rose-chafers, flea-beetles, bark- 

 borers, and fruit and grain weevils are assuredly enough to 

 give the beetles a bad name. But there are good beetles as 

 well as bad ones. The little lady-bird beetles eat unnumbered 

 hosts of plant-lice and scale-insects, the carrion-beetles are 

 active scavengers, and the members of the predaceous families, 

 as the Carabids and tiger-beetles, undoubtedly kill many noxi- 

 ous insects by their general insect-feeding habits. In the later 

 chapters on injurious insects (XXX to XXXVII) many kinds 

 of beetle pests will be described. 



Order Diptera. The Diptera, or two-winged flies, consti- 

 tute another large order of insects, which are characterized, 

 first of all, by their possession of but one pair of wings, those 

 of the meso-thoracic segment, the hinder pair being transformed 

 into two short, slender, knob-ended structures called balancers. 

 These have a special nervous equipment, and have been shown 

 by experiment to have some control of the equilibrium of the 

 fly when in flight. The two wings are membranous, usually 

 clear and supported by a few strong veins. The mouth-parts 

 show much variety, and although no flies can bite in the sense 



