ANIMAL PARASITES 



299 



ovipositor. Another insect, known as the pigeon horn- 

 tail (fig. 236), upon which Thalessa preys, deposits its eggs 

 by means of a strong, piercing ovipositor, half an inch 

 deep, in the trunks of growing trees. The young or larval 

 horn-tail hatches as a soft-bodied white grub, which 

 bores more deeply into the tree, 

 filling up the burrow behind it with 

 small chips. When a female Tha- 

 lessa finds a tree infested by the 

 horn-tail she selects a place which 

 she judges is opposite one of its 

 burrows, 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 (fig. 237). 

 Having reached the horn-tail's bur- 

 row she deposits an &gg in it. When 

 the larva hatches it creeps along 

 the burrow until it reaches and 

 fastens itself upon the larval horn- 

 tail which it destroys by sucking its 

 blood. When full grown it changes 

 to a pupa within the burrow of its host, and finally the 

 adult Thalessa gnaws a hole out through the bark if it 

 does not find the one already made by the horn-tail. 



Almost all birds are infested with small, flattened, 

 wingless, parasitic insects which live among the feathers, 

 and feed by biting off small bits of barbs. Chickens and 

 pigeons are specially infested by these biting bird-lice 

 (called biting to distinguish them from the common true 

 lice of other animals, which have a piercing beak and 

 suck blood) (fig. 238). Specimens of these parasites 

 should be obtained and examined under a microscope to 



Fig. 



bird-lDuse 



{^Nirnms prat'stans) from 

 a tern {Stt-rna maxima). 

 (About one-twelfth inch 

 long; photomicroi^raph 

 by Geo. E. Mitchell.) 



