Enjoying this little air-castle, we began to excavate. Having had experience with the nests of Ammophila and Diodontus, and knowing that the task might not be so easy as it looked, we went to work with all possible care. It seemed, however, that some magician’s trick—some deception of the senses—had been played upon us. We saw the spider interred; we at once dug up the place and found nothing. Slowly and carefully we enlarged our circle. We went down deeper until the opening was large enough to hold a thousand spiders,—still nothing. Then we tried another plan. Gathering all the earth that we had taken out, we sifted it through our hands—in vain. At last we acknowledged ourselves beaten, and trudged home empty-handed.
Our pride was destined to be still further humbled. Three times within that same week we saw the tornado wasp bury her spider, and three times we failed, just as incredibly, to find it. On the last of these occasions we did not let her fill the nest, attempting to follow the tunnel and get out the spider as soon as the egg was laid, but the loose, unstable character of the soil defeated us.
Our fifth example, however, dug her nest, not among the beans but lower down in the potato field, where the ground was firmer; and here we made our first successful excavation,—successful only up to a certain point, since in getting out the spider we dislodged the egg, and although it was at once replaced it never developed. The spider was placed three inches below the surface, but we could not trace the tunnel. At our next opportunity, wishing to make good this failure, we placed a blade of grass in the opening just after the wasp began to fill it. On being disturbed she assumed the most comically threatening aspect, whirling around, lifting her wings, and then circling about us. As soon as we moved back she dashed at the grass-blade and pulled it out with great energy. A few minutes later we made a similar attempt, and again she frustrated our plan; but when we inserted the grass-blade for the third time, the nest being now half filled, she let it remain. Some hours later, with this to guide us, we succeeded in tracing the nest, but much to our disappointment found it transformed into a banqueting hall. Scores of tiny red ants had discovered this rich store of food. They had eaten the egg and were rapidly finishing the spider.
Twice afterward, in opening these nests, we found the same ants in possession before us. It is probable that they are a formidable enemy to this and other species of Pompilus; but they seem to find the spider by burrowing beneath the surface, so that the elaborate hiding of the nest from above cannot be meant as a protection from them.
EXAMPLE OF EPEIRA STRIX THAT HAS BEEN PARALYZED AND HUNG UP ON BEAN PLANT BY POMPILUS QUINQUENOTATUS, THAT IT MAY BE OUT OF THE WAY OF ANTS WHILE SHE DIGS HER NEST
Pompilus quinquenotatus has a decided preference as to the spider that she takes. While Pelopæus and Trypoxylon are entirely indifferent both as to size and species, and the more nearly related Pompilus marginatus takes Thomisus, Drassus, Attus, Agalena or Lycosa, this more fastidious wasp will not be tempted from the spider of her choice. In more than fifty examples the victim in the play was invariably Epeira strix. If she must confine herself to one species she has made a fortunate selection, since there is no other spider so common in our neighborhood, not only in the woods, but around the barns and outbuildings. Most frequently it was the female that was taken, but this does not imply a preference for that sex, since the females are more abundant than the males. We have never seen the spider captured and do not know where the sting is given, but certainly this wasp wounds her prey very severely. The spiders that we took from her were either dead, or so completely paralyzed that it required great care and the use of a magnifying glass to determine that they were alive.
The next stage of her proceedings we are familiar with, as we have frequently seen the wasp carry the spider. Unlike her sister, marginatus, she usually flies with it, and seems not at all encumbered by its weight. In many cases, however, she drags it, holding it by one leg and running rapidly backward.