Bulletin 3 - October 1977: Solitary Wasp (Vespoidea eumenidae)

Solitary Wasp (Vespoidea eumenidae)

One late afternoon in June this year, I was sitting under a tree in the British Embassy Compound when I noticed what at first glance appeared to be a rather odd insect crawling over the sand. On closer inspection it turned out to be a species of solitary wasp that was carrying a caterpillar (or grub -- I'm not sure which) bigger than itself. I had nothing urgent to do so I decided to watch and see what happened next.

After carrying the caterpillar over the sand for about a meter the wasp came upon a few tufts of grass, whereupon, still carrying the caterpillar, the wasp climbed up to where the grass forked out into separate blades. When it reached this point the wasp positioned the caterpillar so that it balanced on the fork, climbed all over it a few times, and then flew down to the sand. During all this time there had been no movement from the caterpillar so I can only suppose that it was either dead or paralyzed.

The wasp then proceeded to excavate a hole in the sand, but this position was obviously not to its liking for it soon left this spot and flew to another place to start all over again. The wasp was still not content and repeated the process many times before returning to one of its earlier efforts completing an excavation to a depth of between 1.5 and 2 inches. From my observations it looked like the excavating was carried out by the use of the wasp's feet, the grains of sand being pushed out and scattered around the hole.

Twice during this excavation period -- which lasted for about 15 minutes -- the wasp returned unerringly to where it had left the caterpillar and seemed to check to see that it was still there. The furthest point that the wasp traveled away from the caterpillar was about two meters, so how did it know where to return to? Was it by scent, or did the wasp mark the spot when it walked all over the caterpillar?

Another interesting point was when the wasp took the caterpillar back to the completed hole it returned there with no hesitation or faltering, so obviously this had been marked also. After depositing the caterpillar in the hole, I assume that the wasp must have laid its egg(s) -- or does it do this before? -- in the caterpillar's body.

The wasp then proceeded to fill back the hole until it was about one half inch from the surface. It then searched around until it found two very small pebbles with which it blocked the entrance, finishing off with more sand and a general smoothing over of the surrounding area.

On subsequent days I noticed other wasps carrying out much the same operations, and once three wasps were busily excavating close to each other.

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With the advent of the cooler weather many insects are re-appearing. Butterflies are again on the wing and amongst those noted recently have been Painted Lady (Vanessa cardui), Plain Tiger (Danaus chrysippus), Pansy Blue (probably Precis orithya), Swallow-tail probably Citrus (Papilio demodcus), a species of Veined White and several small Blues.

At least four species of dragonfly have also been seen; which causes one to wonder about their life cycle in the Emirates. As they spend most of their early life in still or slow moving fresh water, have the ones seen somehow adapted to brackish pools or even salt water? Being strong fliers of course they may well have flown down from Al Ain.

Robber flies were occasionally seen actively chasing and catching small grasshoppers on the wing.