378 



SOME REPRESENTATIVE INSECTS 



Fig. 193.— May-fly, Poly- 



mitarcys albus, one of the 



Order Ephemerida. 



Above, the female hovering 

 with egg-packets extruding. 

 Below, larval stage on a larger 

 scale. (After Needham, from 

 Bull. U. S Bur. Fisheries, 

 Vol. XXXVI.) 



most species. During this brief existence 

 sexual union occurs and the eggs are laid 

 in packets which separate as they sink 

 in the water. The name Ephemerida, 

 which refers to the ephemeral life of the 

 members of this order, is therefore well 

 chosen. The larvae of stone-flies (Plecop- 

 tera) somewhat resemble those of the 

 may-flies, but they are commonly found 

 in streams, attached to the under sides 

 of stones. The adult life is of much 

 longer duration than that of the may-flies. 

 The adult dragon-flies (Odonata), or 

 devil's darning needles and snake-doctors, 

 are more familiar. Wonderfully efficient 

 in their powers of flight, they skim the 

 surface of the ponds in the heat of the 

 day. Although they are often supposed 

 by the ignorant to be dangerous, they 

 are in fact very beneficial to man, since 

 they destroy innumerable small flies and 

 mosquitoes which they catch by darting 

 at them in full flight. Hence the name 

 " mosquito-hawk," which is sometimes 

 applied to these insects, is more appro- 

 priate than the terms mentioned. The 

 larvae of dragon-flies, which are more 

 clumsy than those of the may-flies and 

 stone-flies, are found in ponds and 

 streams, crawling awkwardly about upon 

 the bottom. At the final molting they 

 climb along the stem of a water plant 

 into the air, and after the adult emerges 

 the cast skin of the larva remains cling- 

 ing to this support as evidence that its 

 possessor has left the water and assumed 

 the adult form. The damsel-flies, which 

 are classified with the dragon-flies in the 

 Odonata, are smaller and more delicate of 

 body and wing. 



