ICHNEUMON FLIES. 129 
166, larva of Tremex columba), whose fleshy white larvae 
bore in trees. The adults are large, with a long, saw-like 
ovipositor. In the saw-flies {Te7ithredwid(B, Fig. 167 the 
pear-slug, Selandria cerasi) the larva strongly resembles a 
caterpillar, having eight pairs of ahdominal feet. 
The gall-flies (Fig. 168, Cy^iips) are small Hymenoptera 
which lay eggs in the leaves or stems of the oak, etc., 
Fig. 170.— CEcodoma, or Leaf -cutter Ant of Nicaragua. 
which, from the irritation set up by their presence, causes 
the swelling termed a gall. 
The ichneumon-flies (Fig. 169) are very numerous in 
species and individuals; by their ovipositor, often very 
long, they pierce the bodies of caterpillars, iuserting sev 
eral or many eggs into them; the larvae feed only on the 
fatty tissues of their host, but this usually causes the death 
of the caterpillar before its transformation. 
The family of ants is remarkable for the complexity of 
