Dr. and Mrs. Peckham’s investigations on the instincts and habits of the solitary wasps have been described in a volume[30] worthy to be placed by the side of Fabre’s “Souvenirs.” Their descriptions seem to glow with the warm sunshine, and are redolent of the fresh air which afforded the conditions under which the observations were conducted. We can but regret that, in extracting from their bright pages some of the salient facts, the natural delicacy and grace of their treatment must be lost. For we can only give the dry skeleton which they have clothed with the flesh of lively detail. They enumerate the following primary modes of instinctive behaviour:—
1. Stinging.
2. Taking a particular kind of food.
3. Method of attacking and capturing prey.
4. Method of carrying prey.
5. Preparing nest, and then capturing prey, or the reverse.
6. The mode of taking prey into the nest.
7. The general style and locality of the nest.
8. The spinning or not spinning of a cocoon, and its specific form when one is made.
When the young Pelopœus emerges from the pupa-case and gnaws its way out of the mud cell, with limp and flaccid wings, it responds to a touch by well-directed movements of the abdomen with thrusts of the sting, as perfect as those of the adult. There is clearly no opportunity here for either instruction or experience to afford any intelligent guidance. Stinging is an instinctive act. And it is an act of which great use is made in the capture of prey which shall serve for food to the young—it has a biological end. But the wasps of different species do not have to learn by experience what prey to attack. It is by instinct, too, that they take their proper food-supply, one caterpillars, another spiders, a third flies or beetles. So deeply seated, indeed, is the hereditary preference, that no fly-robber ever takes spiders, nor will the capturer of spiders change to caterpillars or beetles. Some keep to a few species or genera, while Philanthus punctatus preys chiefly or entirely on bees of the genus Halictus.