516 NATURAL HISTORY OF ARTHROPODS. 



species are parasitic. Evania l&vigata was found by Packard to be parasitic 

 upon the cockroach, Periplaneta. Pelednus polycerator is a common species in 

 this country. The members of this genus are remarkable for the great length of the 

 abdomen in the females. 



SUB-OBDEK II. - - ACULEATA. 



In the classification of specimens the Aculeata can be distinguished from the Tere- 

 brantia by the form of the trochanters of the posterior legs ; these consist of two 

 segments each in the Terebrantia, and of a single segment in the Aculeata. This 

 character is much more available for practical use than those which give the names to 

 the sub-orders. 



The Aculeata includes the ants, cuckoo-flies, digger-wasps, true wasps, and bees. 

 The ants (Formicidae) may be recognized by the lenticular shape of the first (and 

 sometimes also the second) segment of the abdomen, and in the winged forms by the 

 absence of tegulae at the base of the wings. The cuckoo-flies (Chrysididae) have only 

 three or four visible abdominal segments (very rarely there is a fifth in the males) ; 

 the body is colored with bright metallic colors, and the wings are without any com- 

 pletely closed cubital cell. In the digger-wasps (fossorial hymenoptera) there is at 

 least one closed cubital cell ; the first discoidal cell is not greatly elongated, and is 

 smaller than the median cell. The wings are not folded when at rest ; tegulae are 

 j tresent, and the first segment of the posterior tarsi is cylindrical. The true-wasps 

 (Vespidae) agree with the digger-wasps in having at least one closed cubital cell, in tin- 

 presence of tegulae, and in the cylindrical form of the first segment of the posterior 

 tarsi, but differ in having the first discoidal cell much elongated and larger than the 

 median cell, and in having the wings folded when at rest. The bees (Apidae) are dis- 

 tinguished from all other Hymenoptera by the form of the first 

 segment of the posterior tarsi, which is more or less enlarged, 

 flattened, and clothed on the inside with hairs for the collection 

 and carrying of pollen. 



The family FORMICID^E or FORMICARIES includes the ants, easily 

 recognized by the well-known form of the body. The only insects 

 which are liable to be mistaken for ants are the white ants belong- 

 ing to the Pseudoneuroptera, and the Mutillidte, which are to be 

 described a little later. But the ants are readily distinguished 

 FIG. 647. Poiyrhachis from these and other insects by the form of the abdomen. The 

 arboricota, worker ma- firgt se g ment o f t i ie abdomen, and in one sub-family the second 



also, forms a lenticular scale or knot varying in form and serv- 

 ino- as a peduncle to the abdomen as shown in our figures of Poiyrhachis and 

 Eciton. 



The ants are social insects ; that is, a large number of them live together in a com- 

 mon nest. Usually each species consists of three forms, male, female, and worker. In 

 a single known genus (Aner gates) there are only males and females. The workers 

 are really females in which the reproductive organs are not fully developed, and which 

 but rarely produce eggs. In many species there are two kinds of workers. One of 

 these differs from the ordinary workers in having much larger heads and more power- 

 ful jaws. These are known as soldiers. "In the sauba ant of South America 

 (CEcodoma cephalotes) the complexity is carried still farther. Bates has shown that 



