“That is very doubtful. A live larva has no odor. And, besides, the most difficult part is not to find out whether or not a suitably plump larva is there under the bark, at such and such a depth; it is also necessary to ascertain whether another ichneumon egg has not already been laid in the body of the coveted worm, as one larva would be insufficient for two nurslings. An egg deposited in some fat worm is not seen, heard, or felt; that is very evident. Nevertheless the ichneumon never plunges its terebra through the bark into a larva already occupied. What guides it? I do not know; nobody knows. Instinct has ways and means unsuspected by our wisdom. An ichneumon alights on the trunk of a tree. The perfectly healthy bark betrays to the sharpest eyes no sign of what the hymenopter is after. Never mind; the insect soon satisfies itself as to whether or not the place is a good one for its purpose. It makes a careful examination, tapping with its antennæ and keeping up a continual vibratory movement. A spot is chosen. The insect plants itself firmly on its legs, draws up its abdomen, and, holding its terebra in a vertical position, plunges the point of it into an imperceptible fissure in the bark. The little auger pierces the bark, though not without effort and occasional pauses, for there are difficulties to be overcome; nevertheless it goes as far as its length permits. The end is attained; the point of the instrument penetrates the flesh of the worm hidden under the bark. The egg being deposited in the incision thus made, the insect withdraws its blade carefully, so as not to break it, and proceeds to lay eggs in the bodies of other larvæ.” “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 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.