THE HONEY BEE 373 



their wings through degeneration. The eggs of the lice are deposited on 

 the hair of the mammal or bird that serves as host ; the young hatch and 

 immediately begin life as parasites, either sucking the blood or feeding 

 on the hair and feathers of the host. In the order Hymenoptera there 

 are several families, all of whose members live during their larval stage 

 as parasites. We may call these hymenopterous parasites, ichneumon 

 ( ) flies. (Fig. 242.) The ichneumon flies are par- 



asites on other insects, especially of the larvae of beetles and moths and 

 butterflies. In fact, the ichneumon flies do more to keep in check the 

 increase of injurious and destructive caterpillars than do all our artificial 

 remedies for these pests. The adult ichneumon fly is four-winged and 

 lives an active, independent life. It lays its eggs either in or on or near 

 some caterpillar or beetle grub, and the young ichneumon, when hatched, 

 burrows into the body of its host, feeding on its tissues, but not attack- 

 ing such organs as the heart and nervous ganglia, w^hose injury might 

 mean immediate death to the host. The caterpillar lives with the ichneu- 

 mon grub within it, usually until nearly time for its pupation. In many 

 instances, indeed, it pupates with the parasite still feeding within its 

 body, but it never comes to maturity. The larval ichneumon fly pupates 

 either w'ithin the body of its host or in a tiny silken cocoon outside of 

 its body. From the cocoons the adult winged ichneumon flies emerge, 

 and after mating find another host on whose body to lay their eggs." 



As an example of a parasite living upon another parasite, though 

 one of these uses a tree as its host, the remarkable ichneumon fly 

 Thalessa (Fig. 242) is an excellent example. This animal, which has a 

 very long, slender, flexible ovipositor, finds a spot in a tree \vhere the 

 insect Tremex columba ( ), commonly called the 



pigeon horntail, has deposited its eggs about a half inch below the sur- 

 face of a growing tree. When these eggs are converted into larva, the 

 larva digs still deeper into the tree, filling up the open space behind it 

 with tiny chips. Through a very extraordinary instinct the Thalessa 

 finds the spot opposite where the Tremex larva lies and "elevating her 

 long ovipositor in a loop over her back, with its tip on the bark of the 

 tree, she makes a derrick out of her body and proceeds with great skill 

 and precision to drill a hole into the tree. When the Tremex burrow is 

 reached she deposits an egg in it. The larva that hatches from this egg 

 creeps along this burrow until it reaches its victim, and then fastens itself 

 to the horntail larva, which it destroys by sucking its blood. The larva 

 of Thalessa, when full grown, changes to a pupa within the burrow of 

 its host, and the adult gnaws a hole out through the bark if it does not 

 find the hole already made by the tremex." 



Practically all the mites ( ) and ticks ( ), 



animals closely allied to the spiders, live parasitically. 



