I was not the only one to profit by its shade; my companions were usually numerous. Gadflies of different kinds would take refuge under the silken canopy, and roost peacefully here and there on the outspread silk, rarely failing to appear when the heat was overpowering. To pass the hours when I was unemployed, I used to observe with pleasure their great gilded eyes shining like carbuncles under my canopy, or their grave movements when some spot [[239]]of their ceiling became too much heated, and they were forced to move a little way.
One day—ping! ping! the tense silk was resounding like the parchment of a drum. Perhaps an acorn has fallen on my umbrella. Soon after, close together, came ping! ping! Has some idle jester come to disturb my solitude, and fling acorns or little pebbles on my umbrella? I came out of my tent and inspected the neighbourhood. Nothing! The blow was repeated. I looked upward, and the mystery was explained. The Bembecids of the neighbourhood, which prey on gadflies, had found out the rich store of food which was keeping me company, and were darting audaciously under my shelter to seize the gadflies on the ceiling. Nothing could have been better. I had only to keep quiet and observe.
Every moment a Bembex entered like a sudden flash, and darted up to the silken ceiling, which resounded with a dull thud. A tumult went on aloft, in which one could not distinguish attacker from attacked, so lively was the mêlée. The struggle was very brief; almost at once the Hymenopteron retired with a captive between its feet. The dull band of gadflies drew a little back all round on this sudden irruption, which decimated them, but without leaving the treacherous shelter. It was so hot outside; wherefore move? Plainly, such swift attack and prompt departure with the prey does not allow the Bembex to use a poignard according to rules. The sting no doubt fulfils its office, but is directed with no precision towards such spots as are exposed by the chances of the combat. To slay outright the [[240]]half-murdered gadfly, still struggling between the feet of its assassin, I have seen the Bembex chew the head and thorax of her victim. This habit, peculiar to the Bembecids, shows that the Bembex desires death, not paralysis, since she ends the life of the Diptera with so little ceremony. Everything considered, I think that on the one side the nature of the prey, so quickly dried up, and on the other, the difficulties of so vehement an attack, are the reasons why the Bembecids serve up dead prey to their larvæ, and consequently provide it daily.
[To face p. 240.
BEMBEX ROSTRATA TAKING GADFLY TO ITS NEST; BEMBEX ROSTRATA MINING
Let us follow the Hymenopteron when it returns with its captive closely clasped to the burrow. Here is one—B. tarsata—coming loaded with a Bombylius. The nest is placed at the sandy foot of a vertical slope, and the approach of the Bembex is announced by a sharp humming, somewhat plaintive, and only ceasing when the insect has alighted. One sees her hover above the bank, then descend, following the vertical line slowly and cautiously, still emitting the sharp hum. If her keen gaze should discover anything unusual, she delays her descent, hovers a moment, ascends again, redescends, then flies away, swift as an arrow. In a few moments she returns. Hovering at a certain height she appears to inspect the locality, as if from the top of an observatory. The vertical descent is resumed with most circumspect deliberation; finally, she alights without hesitation at a spot which to my eye has nothing to distinguish it from the rest of the sandy surface. The plaintive note ceases at once. She must have alighted somewhat by chance, since the most practised eye could not distinguish one spot from another [[241]]on the sandy tract. She will have dropped down somewhere near her hole, whose entrance she will now seek, marked since her last exit not only by the natural falling in of materials, but by her scrupulous sweeping. No! she does not hesitate in the least—does not feel about—does not seek. All have agreed that the organs fitted to direct insects in their researches reside in the antennæ. At the moment of returning to the nest I see nothing special in their play. Without once losing hold of the prey the Bembex scratches a little in front of her just where she alighted, pushes with her head, and straightway enters clasping the Dipteron to her body. The sand falls in, the door closes, and the Hymenopteron is at home.
I have watched the Bembex return home a hundred times, yet it is always with fresh astonishment that I see the keen-sighted insect at once detect an entrance which nothing indicates, and which indeed is jealously hidden—not indeed when she has entered (for the sand, more or less fallen in, does not become level, and now leaves a slight depression, now a porch incompletely obstructed), but always after she comes out, for when going on an expedition she never neglects to efface the traces of the sliding sand. Let us await her departure, and we shall see that she sweeps before her door and levels everything scrupulously. When she is gone, I defy the keenest eye to rediscover the entrance. To find it when the sandy tract was of some extent I was forced to have recourse to a kind of triangulation, and how often did my triangle and efforts of memory prove vain after a few hours’ absence! I [[242]]was obliged to have recourse to a stake—in other words, a grass stalk planted before the entrance—a means not always effectual, for it often disappeared during the frequent settings to rights of the outside of the Bembex’s nest. [[243]]