SPIDER-LIKE ANIMALS AS PARASITES 195 
larve of caddis-moths. Others (species of Rhyssa and Thalessa, 
fig. 1140) possess powerful ovipositors three or four inches 
long, with which they penetrate trees tunnelled by the larve 
of wood-wasps (Szvzczde). The grubs which hatch out from 
the eggs of such ichneumons attach 
themselves as external parasites to 
the wood-boring larve. Fabre has 
described the even more remarkable 
habits of another parasitic form (Leu- 
copsts gigas), that seeks the nests of the 
Mason - Bee (Chakcodoma 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 Fig, 1140.—A Female Ichneumon-Fly 
; : : (Thalessa) using her Ovipositor 
the contained cells, 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. 
SPIDER-LIKE ANIMALS (AracHunipa) 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 (/vodes ricznus). Fig, srar. A Tick 
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. 
