CRABRO STIRPICOLA
Many species of Crabro make their nests in the stems of plants, and among these is stirpicola, which is seen in numbers, through the middle of July, flying about in a leisurely way, though it is only toward the end of the month, or in the early days of August, that they settle down to the work of making their homes. On the afternoon of July twenty-seventh, after some very lively work in the heat of the day, we walked down to the berry garden at half past five o’clock, rather to rest ourselves than with the thought of undertaking anything new; but a wasp-hunter cannot afford to choose his own hours, and we thankfully accepted the sending of fortune when we came upon a stirpicola busy at work in digging out her nest. She had only begun to excavate, and had reached a length just equal to that of her own body. Her manners were an agreeable contrast to those of the wasps that we had been watching through the day. The feverish excitement of their ways seemed quite in keeping with the burning heat of noon, while Crabro’s slow and gentle movements harmonized perfectly with the long shadows of evening. To fully appreciate the difference between Pompilus or Ammophila and Crabro it is necessary to see them at work. The one is the embodiment of all that is restless, vying with the humming-birds in swiftness and energy, while the other is calm, quiet, and stately in all that she does.[ill-107]
BOTTLE ON STEM TO MEASURE WORK OF CRABRO
Some ten feet away was a second stirpicola, and this one, to judge from the depth to which she had penetrated, must have been at work for about two hours. We watched them both, and saw them bring up load after load of pith. They bit out the pellets with their mandibles, and passed them back between the legs and under the body until a quantity had accumulated above the tip of the abdomen. They then walked backward up the stem, and thus pushed out the mass as they came to the top. Often they used the hind legs to assist in getting it out of the way, sometimes kicking it to a little distance. Once in every two or three trips they would come out far enough to expose part of the thorax. They appeared and disappeared with the regularity of a machine, never stopping to rest.
We remained with them until seven o’clock, when we placed a long bottle over each stem in such a way that while it did not interfere with the work of the wasp, it caught the chips of pith as they fell out. At the end of an hour we noted the amount of accumulation in the tube, and thus had a measure of their rate of work. The drawing gives an idea of the arrangement of the tube on the stem. When we left them they were still digging and delving.
At half past nine we took a lantern and went down to visit our charges. We expected to find them at rest, and asleep; but on the contrary they were working as busily as ever, and upon examining the measuring glasses we found that they had not paused since we left them. We measured the depth of the débris in the bottles, and then emptied them.
At four o’clock on the next morning we went to the garden, and were much surprised to find that the two wasps had worked without intermission throughout the night. Indeed they seemed to have shortened a little the time that it took to make a round trip down the gallery and up to the opening again, since there was more pith in the bottles than we could have expected if they had worked at only their former rate. Neither the coolness of the air nor the darkness of the night had made the slightest difference to them. After watching them a few minutes, and marveling at their powers of endurance, we cleared out the tubes and returned to bed. At half past eight we found them still at work. Unlike us, they had taken no morning nap, but had gone on with their tunneling in their usual steady way.