170 ELEMENTARY ZOOLOGY 



water-scavenger beetles hatch as elongate, wingless, 

 active larvae, provided with three pairs of legs and strong 

 jaws. They remain for a short time after hatching in the 

 egg-case, feeding on each other ! After they issue from 

 the case they feed on flies or other insects which fall into 

 the water, and on snails. They breathe through a pair 

 of spiracles situated at the posterior tip of the abdomen, 

 coming to the surface and thrusting this tip up so that the 

 spiracles are out of water. They grow rapidly, molting 

 three times before becoming full grown. They attain a 

 length of nearly three inches. -When full grown they 

 leave the water, crawling out on the damp shore of the 

 pond or stream, and burrow into the soil for a few inches. 

 Here they molt again, or pupate as it is called, changing 

 to a non-feeding, quiescent stage called the pupal stage. 

 The pupa is the stage in which the great changes from 

 wingless, crawling and swimming, short-legged, long, 

 slender-bodied larva to winged, swimming and flying, 

 long-legged, compact, broad-bodied adult are completed. 

 Late in the summer or in the fall the pupal skin breaks 

 and the adult issues. It works its way to the surface of 

 the ground, and betakes itself to the nearest water. 



The water-scavenger beetle shows in its post-embryonal 

 development a " complete metamorphosis " as contrasted 

 with the "incomplete metamorphosis" of the locust. 

 Wherever among insects similar changes occur, the young 

 issuing from eggs as larvse only remotely resembling the 

 parent, and these active feeding larvae changing finally 

 into more or less quiescent, strictly non-feeding pupae, 

 which finally change into the active adults, a complete 

 metamorphosis is said to exist. All the beetles, the 

 butterflies and moths, the two-winged flies, the ants, bees 

 and wasps, and certain other groups of insects undergo in 

 their post-embryonic development a complete metamor- 

 phosis. The crickets, katydids, the sucking bugs, the 



