VI INSECTA 243 



and galleries constructed of the faecal remains of woody matter passed 

 through the alimentary canal, or of earthy material. Some species do 

 much damage in tropical countries by excavating woodwork until nothing 

 is left but a thin outer shell. 



Many of the Neuroptera such as the dragon-flies, may-flies, and 

 caddis-flies have aquatic larvae and in such cases the life of the mature 

 fly (imago) may be very short. The adult flies often form favourite food 

 of fresh-water fish (Perlidae — " stone-flies " ; Epheraeridae — may-flies, 

 "duns," "spinners"; Sialidae — alder-flies; Phryganeidae — caddis- 

 flies). As is well known to fishermen the last ecdysis, resulting in the 

 emergence of the adult fly, is liable to occur in large numbers of individuals 

 about the same time. Over tropical rivers (New Guinea, Paraguay) 

 what looks like a thick snowstorm may sometimes be observed, caused 

 by the emergence from the water of myriads of snowy- white may- flies. 



The CoLEOPTERA or Beetles may be said to be the predominant order 

 of insects at the present day. About 150,000 species have already been 

 catalogued. The typical beetle possesses clearly marked characteristics. 

 The thickness and hardness of the chitinous exoskeleton reaches here its 

 maximum development. The anterior wings are purely protective in 

 function, forming the thick elytra the edges of which fit accurately 

 together along the middle line of the back. The mouth-parts are of the 

 biting type and the life-history shows well-marked metamorphosis — the 

 larva being a grub or maggot, and the pupa usually having a soft cuticle 

 and showing distinctly the appendages and other external features of 

 the adult. 



Some beetles do damage by attacking crops, stored grain, timber, 

 furniture, but for the most part the Coleoptera are insects which do not 

 come into any important direct relation to man. 



The Hymenoptera are especially characterized by the hooking 

 together of the fore- and hind-wing on each side so that they work as if 

 they were a single continuous wing. The mouth-parts are adapted for 

 biting, licking and sucking. In the female the hind end of the body 

 carries long slender projecting pieces which form an ovipositor for deposit- 

 ing the eggs in crevices or in holes bored by it for the purpose. In the 

 Bees, Wasps and Ants, the ovipositor has given up its original function 

 and become a weapon — the sting. The poison (Formic Acid) which adds 

 pain to the wound possibly served as an antiseptic secretion when the 

 ovipositor . performed its original function. In the life-history of the 

 Hymenoptera there is well-marked metamorphosis, the larva being a 

 grub and the pupa showing clearly the projecting appendages and other 

 features of the adult. 



