CLASS INSECTA 



283 



wooden blocks or directly upon the ground. It has long been a source 

 of speculation as to how these insects can digest the cellulose of the 

 wood, which few other animals are able to do. It has recently been 

 discovered that it is because of the presence of symbiotic intestinal 

 Protozoa which change the cellulose so that the termites can use it. 

 In the absence of this protozoan the termite is helpless and dies, and the 

 protozoan seems not to flourish outside the alimentary canal of the 

 termite. 



Being vegetable feeders and likely to attack growing crops, locusts 

 have affected man since the very beginning of agriculture. Migrations 



YvG. 181. — A termite, Reticulotermes flavipes Kollar. A, winged male. B, larva. 

 C, dealated queen. D, soldier. E, queen of a tropical African species. (A to D, from 

 Bruner, "Study of Entomology," after Riley; E, from, Kellogg, "American Insects," after 

 Nassonow, by the courtesy of Henry Holt & Company.) A to D, X 4; £^, natural size. 



of locusts from arid regions into those under cultivation have frequently 

 been recorded in history, accompanied by marked economic results, in 

 some cases even causing large numbers of people to move from the region 

 thus affected. Locusts belong to the order Orthoptera (or thop' ter a; 

 G., orihos, straight, and jAeron, wing), which also includes cockroaches, 

 mantids, walking sticks, katydids, and crickets. 



Many different types of insects are known as lice. What are called 

 biting lice are found on birds and mammals. They do not bite their 

 hosts but eat feathers, hairs, and epidermal scales. Their presence 

 on the animal, however, occasions irritation, and it is to allay this 

 irritation that birds are in the habit of dusting themselves. The sucking 

 lice possess probosces which can puncture the skin of their hosts, which 

 are birds and mammals. They attack domestic poultry but come 

 upon them only at night, hiding in crevices in the poultry houses-during 

 the day. 



