INSECTA 



493 



In such a large order of insects it is to be expected that all manner 

 of habit and food will be found. Beetles occur in large numbers in 

 water, soil, and plant tissues. Circumscribed environments like dung, 

 rotting vegetation, wood and fungi are never without prominent 

 coleopteran associations. A large number, such as many coccinellids 

 (lady birds), carabids, e.g. Carabus violaceus, and staphylinids, e.g. 

 Ocypus olens, are carnivorous and to this extent useful insects. On the 

 other hand, among the phytophagous forms are to be found some of the 

 most serious agricultural pests, the boll weevil, Anthonomus grandis, 

 causing so much damage to the cotton crop in America that it has 



Fig. 340. External anatomy of Calosoma semilaeve, with left elytron and wing 

 extended. After Essig. aw. antenna; e/. elytron; />. palp; 5^. spiracles. 



been seriously proposed to cease growing cotton for a period of time 

 in order to eradicate this pest. A large number cause considerable 

 damage to timber, probably the most notable being Xestobiiim riifo- 

 villosum, the death-watch beetle, destructive to structural timber. 



The order falls into tw^o suborders, the Adephaga and the Polyphaga. 



The Adephaga are distinguished by filiform antennae, a five- 

 jointed tarsus and a larva of the campodeiform type, with a tarsus 

 bearing two claws. 



To this group belong those families including the large water 

 beetle Dytiscus, the ground beetles Carabus and Calosoma (Fig. 340), 

 the tiger beetle Cicindela, and the aquatic whirligig beetles Gyrinus. 



