190 ANIMAL LIFE 
pigeon horn-tail (Zremex columba) (Fig. 117) deposits its 
eggs, by means of a strong, piercing ovipositor, half an inch 
deep in the trunk wood of growing trees. The young or 
Fic. 116.—Caterpillar with cocoons of the pups of ichneumon fly parasites, and 
(above) one of the adult ichneumon flies, The lines indicate natural dimensions. 
larval Tremex is a soft-bodied white grub, which bores 
deeply into the trunk of the tree, filling up the burrow be- 
hind it with small chips. The Thalessa is a parasite of the 
Tremex, and “when a female Thalessa finds a tree infested 
by Tremex, she selects a place which she judges is opposite 
