Long-tailed Ophion, natural size
(One of the Ichneumonidæ)
“Then the great length of this blade,” Jules remarked, “though at first it seems unhandy for the creature, is on the contrary perfectly fitted for the work to be done. With too short a terebra the ichneumon couldn’t reach the larvæ under the bark and even in the wood itself.”
“From the length of the terebra one can estimate at what depth, as a rule, the eggs are laid. Ichneumons with a long terebra lay their eggs in larvæ protected by a thick layer of bark or wood or earth or other material; those with a short terebra seek larvæ living in the open air, such as caterpillars for example. However, if the caterpillar is covered [[353]]with long hairs, thus keeping the ichneumon at a distance from the skin of its victim, a long implement is still necessary to convey the eggs into the flesh. But for smooth-skinned caterpillars without any defense the ichneumon is furnished with a very short terebra, often invisible when not in action, so that the end of the insect’s abdomen must be pressed in order to make the egg-conveyer show itself, be it lancet, saw, fine blade, or other instrument of that sort.
“The ichneumon on the hunt is one of the most curious sights imaginable. Caterpillars are peacefully browsing on leaves. An ichneumon comes along, flies about over them, selects the ones that look best for its purpose, and never fails to exclude those that already have eggs in their bodies. At the sound of their enemy’s wings the terrified caterpillars stop eating and begin to move their heads in a startled manner from side to side, doubtless in the hope of frightening off the foe. But the latter pays no attention to these vain threats; it alights on the caterpillar of its choice and, so quickly that you hardly have time to see the operation, darts its terebra and lays an egg in the wound.”
“And doesn’t the caterpillar make any resistance?” asked Emile.
“It performs some lively antics, but that is all. The poor creature cannot defend itself against an enemy in the air, a winged enemy that can always keep at a safe distance and is always ready to fly [[354]]away. The other eligible caterpillars in the group are attacked in the same manner, one by one, until the ichneumon has laid all its eggs.”
“Each caterpillar gets only one egg?” asked Jules.
“That depends on the size of the egg-layer. If it is large it lays but one egg in each caterpillar, so that the larvæ may each have enough food; if small, it lays several.”