A month later we found Crabro lentus nesting in the ground. Her tunnel ran down obliquely for six and one half centimeters, and had an enlargement at the end. Two bugs and a fly were in the nest, when we opened it before the provision was completed. To find sexmaculatus taking both flies and gnats was surprising, so rigid are the family traditions of the wasps; still, she might feel that so long as she drew the line at Diptera she was all right. But to believe that one wasp, a Crabro, too, with all the marks of conservatism about her, would take such diverse things as bugs and flies, is almost too much to believe. It is true that Crabro wesmæli is said to use both flies and bugs;[4] but some accident may have led to this supposition, and stronger evidence is needed to prove that there is variability in so deeply seated an instinct.
CRABRO AND HER WHITE MOTHS
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The Crabro wasps all have pleasant ideas as to where they want to live, but interruptus excels in the choice of a dwelling place. We lately found ten or twelve of them in Milwaukee, nesting in an old log on the shore of Lake Michigan, and when they opened their doors in the morning they had before them the splendor of the great bay; but calm in the midst of the glory they never paused on the threshold, as Cerceris would have done, to take a look at the world before going to work. One morning the earliest riser in our little colony was beginning the day at half past nine. Of good size for a Crabro, with a square determined-looking head and very direct and business-like manners, she proceeded to cut out a new chamber for provisioning. These chambers are nothing more than enlargements of the long gallery, such as are made in stems by related species. At ten o’clock she departed on a hunting excursion among the bushes on the bank above us, and came back in eight minutes, carrying, much to our surprise, a white-winged moth, which was clasped under the body by the second and third pairs of legs, and was passed back to the third pair as she alighted before entering. A moth is an innovation, a delicacy new to the accepted idea of what a Crabro larder, accustomed to Diptera, should contain. A moment later she was off again, but this time did not succeed so quickly, coming back twice empty-handed for brief visits, and bringing in a load at the end of half an hour. It took six moths to provision the cell, and as the number neared completion her interest and energy seemed to wax greater, the hunting intervals shortening to five, and even to two minutes. We found afterwards that some of the moths were alive and some dead, and that she packed them lengthwise, one after another, into the closely fitting chamber. At a little before eleven o’clock the cell was filled, and the wasp retired from sight, closing the door behind her. We thought that she was resting, but presently the protrusion of wood dust showed that she was enlarging her house, and an hour later she came out and began to hunt again. By this time half a dozen were working. Before leaving for the first time in the morning each one made a thorough study of the place, and on returning they entered their own doors, which were standing open, without hesitation, the long white wings of the moths trailing behind them. Four species were represented in the nests that we opened.[ill106]