SPIDER-LIKE ANIMALS AS PARASITES 



195 



larvae of caddis-moths. Others (species of Rhyssa and Thalessa, 

 fig. 1 1 40) possess powerful ovipositors three or four inches 

 long, with which they penetrate trees tunnelled by the larvae 

 of wood-wasps (Siricidce). The grubs which hatch out from 

 the eggs of such ichneumons attach 

 themselves as external parasites to 

 the wood-boring larvae. Fabre has 

 described the even more remarkable 

 habits of another parasitic form (Leu- 

 cop sis gigas], that seeks the nests of the 

 Mason -Bee (Chalicodoma muraria), 

 in which a number of cells, each 

 containing a larva, are surrounded by 

 little stones cemented together (see 

 p. 53). The parasite thrusts her stout 

 ovipositor through weak spots in 

 this masonry, never failing to reach 

 the contained cells 3 in each of which 

 she deposits an egg. It is only when such a cell contains a full- 

 grown bee-larva, on the point of becoming a pupa, that the 

 operation attains the desired object. In this case the parasitic 

 grub first wanders round the cell to destroy any other eggs that 

 may have been there deposited, and then attaches itself to the 

 bee-larva, the juices of which nourish it for two or three weeks. 

 Next follows a quiescent period of ten or eleven months, after 

 which the larva becomes a pupa, from which the perfect insect 

 soon emerges. 



Fig. 1140. A Female Ichneumon-Fly 

 ( Thalessa} using her Ovipositor 



SPIDER-LIKE ANIMALS (ARACHNIDA) AS PARASITES 



Many of the Ticks and Mites (Acarina) are parasitic upon 

 other animals, and some of them have earned con- 

 siderable notoriety on this account. Ticks are 

 greedy blood-suckers which lurk on plants, and 

 attach themselves to passing birds or mammals, 

 human beings not excepted (fig. 1141). One of the 

 best-known species is the Dog-Tick (Ixodes ricinus). 

 A victim once secured, the tick buries its piercing 

 mouth-parts in the skin, and takes in so much blood that it swells 

 visibly. When satiated it drops off, and digests the meal at leisure. 



Fig. 1141. A Tick 

 (Ixodes}, enlarged 



