HYMENOPTERA 



177 



of ichneumon flies has its special host, the majority of them being cater- 

 pillars. The largest insect of this family belongs to genus Thalessa. 



Thales'sa luna'tor has a body 1\ inches long and the insect measures 

 nearly 10 inches from the tips of the antennae to the end of the ovipositor, 

 and is parasitic upon the larva of Tremex columba. The ichneumon fly 

 bores a hole with its flexible ovipositor, which is 6 inches long, into the tree 

 infested by Tremex, and deposits its eggs in the burrow of the Tremex larva. 

 When the ichneumon larva hatches, it creeps along the burrow until it 

 reaches its victim, the horntail larva, 

 to which it attaches itself and feeds 

 upon its juices. Sometimes the female 

 ichneumon fly gets her ovipositor fast 

 in the wood and it holds her a prisoner 

 until death. 



Other important, though usually 

 small, parasitic Hymenoptera are the 

 braconids, the ensign-flies, and the 

 chalcid-flies. While the larvae of para- 

 sitic Hymenoptera are degenerate in the 

 same way as the footless, eyeless, an- 

 tenna3less maggots of house-flies, they 

 are not more so. Their parasitic habit 

 has led to no such extraordinary struc- 

 tural specialization through degenera- 

 tive loss, or reduction of parts as is the 

 usual condition in other parasites. The 

 adult is active and well developed. 



The Stinging Hymenoptera. The fe- 

 males and sterile workers, where there 

 are such, have the ovipositor developed 

 into an organ of defense, the sting. 

 Females may be distinguished from the 



Fig. 146. Pimpla in the act 

 of ovipositing on cocoon of tent 

 caterpillar. Somewhat enlarged. 

 (After Fiske.) 



males by having six segments in the abdomen instead of seven. The 

 group includes ants, wasps, and bees. 



Ants live in all lands and in very various conditions and occupations. 

 All of the 2500 or more species live in communities, and division of labor 

 among kinds of individuals and, consequently, differentiation of structure, 

 are highly developed. Ants are easily recognized by the form of the body, 

 but they are distinguished from other insects by the character of the first 

 one or two segments of the abdomen. These are expanded dorsally into a 

 " lens-shaped scale or knot," which varies in form and serves as a peduncle 

 to the rest of the abdomen. 



The ants' nests or formicaries are composed of irregular rooms and gal- 

 leries which may be mostly underground, or have a large portion above 

 ground, as a mound or ant-hill, or may be tunnelled out in the wood of de- 

 cayed trees. " In the tropics," says Comstock, " a greater variety of these 

 structures occur than in our country. . . . One colony of one species 

 has been known to have two hundred mounds covering several hundred 

 square yards. Ants are also very good road makers, sometimes making 

 clean beaten paths or working out covered ways under rubbish." 



There are always three classes of ants (Fig. 147) in a community, w r inged 

 males and females, and wingless workers, sometimes also the soldiers and 

 wingless, but fertile males and females. The winged males and females at 



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