Our conclusions, then, as to Ammophila’s methods of stinging agree fairly well with those of Fabre; but there is one important exception. In his cases the middle segments, upon one of which the egg is laid in our species as well as in his, were invariably stung, and this he considers a point of extreme importance. In one of our cases the middle segments were not touched.[ill-27]
CATERPILLAR WITH EGG OF AMMOPHILA URNARIA
The point in which our observations differ most widely from those of Fabre is in the condition of the caterpillars after the stinging. He seems to have found that they always lived a long time, but in a motionless or nearly motionless state; and he dwells at length upon the necessity of both of these conditions, since he believes that while the wasp larva must have perfectly fresh food, any violent motion would imperil its safety. As a matter of fact we found a wide variation in the thoroughness with which the wasps performed their task. We had, in all, fifteen caterpillars upon which urnaria had worked her will; and while a few of them fulfilled to a nicety the conditions which Fabre believes to be imperative, most of them were far from doing so. Some of them lived only three days, others a little longer, while still others showed signs of life at the end of two weeks. Urnaria stores two caterpillars, and in more than one instance the second one died and became discolored before the first one was entirely eaten. The wasp larva did not, as might have been expected, find fault with this arrangement, but proceeded to attack number two with good appetite, ate it all up, and then spun its cocoon as though nothing unpleasant had occurred.
The second condition was also violated. In one case the bite of the newly hatched larva caused the caterpillar to rear upon end in so violent a manner that it looked as though the little creature would surely be dislodged. Another caterpillar kept up a continuous wriggling without any external stimulation, and when it was touched it rolled about almost as these larvæ do in a healthy state, and yet the egg was not shaken off. The caterpillar which received but a single sting, although not motionless, would have been a safer repository for the egg than either of these. Others fulfilled Fabre’s condition perfectly, lying immovable except when stimulated, and then responding only by a slight quivering of the legs or skin.
Among the fifteen caterpillars that we have taken from the nests of urnaria three kinds are represented, twelve of them belonging to one species, two to the second, and one to the third.
The egg, which is laid upon the side of the sixth or seventh segment, hatches in from two to three days; the larva spends from six days to two weeks in eating, and then spins its pale yellowish cocoon.
