384 SOME REPRESENTATIVE INSECTS 



larval stage they crawl down the plants and burrow in the ground 

 before undergoing the molts that produce the pupae. In a week or 

 ten days this pupa molts into the adult which emerges from the 

 ground to renew its depredations. In the latitude of Missouri, 

 there are three such broods each year, the larvse of the last one 

 crawling underground to pass the winter. Taken as a group, 

 the beetles, like the butterflies and moths, present a bewildering 

 array of species adapted for many diverse conditions. Predacious 

 beetles haunt the ponds and streams in larval and adult stages; 

 others bore into wood, particularly in their larval stages. The 

 June-beetles live in the ground as fat, white grubs, pupating in 

 the spring and emerging as the adults which blunder against our 

 lamps. 



Diptera. — The house-fly, Musca domestica (Fig. 198), is perhaps 

 the most familiar of all insects, and now that it has been recognized 

 as a carrier of the germs of disease its life cycle is becoming widely 

 known. Like other Diptera, it has only the anterior pair of wings, 

 but the posterior pair are represented by the " balancers," which 

 are believed to function in maintaining the equilibrium of the 

 body. The ubiquitous habits of this species are well known. 

 The mouth parts are adapted for biting and lapping, and the fly 

 feeds upon almost any kind of organic matter that may be exposed 

 in the household. As it may easily frequent exposed closets, 

 drains, cuspidors, and similar places, a house-fly may carry on its 

 feet and mouth parts the germs of typhoid fever or other diseases 

 that have recently passed from a human patient. If it feeds at 

 our tables a few hours later, there is great danger of infection; 

 for it can be shown by letting a fly walk across a sterile plate of 

 gelatin, such as is prepared for bacteriological studies, that almost 

 every footprint is later marked by colonies of bacteria that spring 

 up along its trail. House-flies lay their eggs in various forms of 

 decomposing organic matter, but most readily in stable manure. 

 The larvaj, or maggots, which hatch from these eggs in about six 

 hours grow for five or six days before the pupation. The skeleton 

 of the pupa is a tough membrane from which the adult fly emerges 

 in about five days. In this manner a generation may be devel- 

 oped every twelve days under favorable conditions, and since each 

 female lays about one hundred eggs the potential multiplication in a 

 single season is appalling. House-flies hibernate over the winter 

 in the adult stage by crawhng into protected places. The slogan 



