Life and Habits of Common Digger Wasps

246

OBSERVATIONS

SMALL and ESSEX SKIPPERS (Thymelicus sylvestris Poda and T. lineola Ochs.). These two butterflies are always common in Suffolk, particularly the former, but it was noticed this last summer that there were considerably more than usual. Here again it is possible that the absence of rabbits may have been the indirect cause, as the favourite foodplant of the larvae, the cat's tail grass (.Phleum pratense) was left to grow without disturbance.

S.

BEAUFOY.

SOME OBSERVATIONS ON THE LIFE AND HABITS OF THE COMMON DIGGER WASP Oxybelus uniglumis Linn.

I have occasionally found these small black and white solitary females excavating their nests near to each other in a disused gravel pit at Bury St. Edmunds, usually in sand brought down at the pit face by the action of the weather. When excavating, as in all their movements, they were extremely quick ; usually one or more shallow nest-holes were excavated before a permanent site was selected. They dug rapidly into the sand with the forefeet, the sand passing under the body in a continuous stream as they quickly disappeared. The entrance became blocked and remained so throughout, only the damp sand which was occasionally pushed out gave the position. Dßring this work an occasional rest was taken, and on returning to the surface they spent some time exercising the wings and in making a survey of the surroundings. When the required depth had been reached, they returned to the surface, and the entrance was immediately sealed ; this was meticulously carried out by scraping the loose sand with the forefeet, the sand passing under the body back towards the nest in short stages. When sufficient had been deposited the work of Welling commenced : this was performed by running over it in various directions—the mid- and hind-legs appeared to be spread and dragged, frequently resting flatly and directly over it.

When completed, it could only then be located by some mark such as a stone or a dried grass bent. On the completion of this work the bearings for homings were taken, at first by short and then longer flights, back and forth at various angles around the nest.

Each time the wasps returned, they rested flatly over it. When returning from the longer flights they usually alighted a short distance away, completing the journey by running over the sandy floor, occasionally resting and appearing to note every plant and stone by the way.

LIFE AND HABITS OF COMMON DIGGER WASP

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They next proceed to hunt and capture flies with which to Provision the cells. The flies were paralysed and transported to the nests by flight; they were held rigid, head foremost, impaled upon the sting and in consequence tilted slightly on one side ; the wings of the wasp upon alighting closed partly over the fly.

In each of the two nests only one cell was found. In these the flies were packed tightly, lying with the heads pointing away from the entrance. Both contained flve flies of the species Fannia manicata Mg. When approaching the nests with their prey the wasps were ever watchful for and harassed by the parasitic fly Sphixapata = Sphegapata conica Fall., whose numbers were such that they appeared to be everywhere. Usually they were observed waiting motionless upon stones for the return of the victim and when the returning victim passed with its prey, one would quickly rise and follow closely. The wasps always appeared to be aware of the parasites' presence and made determined evasive movements to escape : this appeared impossible when they remained in the open. If however, when approaching the nests, they alighted a short distance away and moved towards them by crawling around stones or through and under the foliage of plants, they were usually successful. DĂźring this method of approach the wasps would occasionally turn suddenly, often completely round, as if to make certain that no Sphixapata conica were following.

The method employed to unseal and reseal the nest was urgently carried o u t ; to enter, the prey was slightly raised upon the sting, to allow the displaced sand to pass under. Only enough was displaced with the forefeet to allow the body and its prey to pass through, as the entry progressed loose sand was continually falling behind, the wasp thus disappearing quickly and the nest being resealed. It was at the moment before the complete disappearance of the wasp's prey that the waiting Sphixapata conica darted forward, presumably to deposit its ova, and was lost in the falling sand.

REMARKS : This species of wasp does not appear to be as common as its name suggests : having searched all the likely habitats, I found all uninhabited except one, a large area of Sandy heathland at Culford, where two were observed during August, 1953. The hazards against its survival in large numbers are many; the two which appear most frequent and are probably fatal are the parasitic species of diptera which prey upon them and the shifting of sand and soil by the action of the weather, for many nests were buried in the gravel pit at various depths from six inches to three feet; from these depths it appears to be beyond the power of the newly emerged wasps to dig themselves free.

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LIFE AND HABITS OF COMMON DIGGER WASP

All the nests under Observation were in positions that received the fĂźll rays of the sun at its hottest. When these were cut off by clouds, the hunting activities ceased until they reappeared.

Specimens of the diptera mentioned were identified by our member Dr. C. D. Day. One specimen was taken on West Stow Heath, 31st July, 1955.

H E N R Y J. BOREHAM.

SOME OBSERVATIONS ON THE LIFE AND HABITS OF THE SILYER SPRING DIGGER WASP Oxybelus argentatus Curt.

I have occasionally observed the solitary females of this species on West Stow Heath, Breckland. Two in July, 1952, and four in July, 1955, usually on those parts which have little Vegetation.

These are probably the first records of its presence in Suffolk.

Of two nests under Observation one was situated on the flat sandy surface and the other in the side of a shallow hole, and were five and six feet respectively from the surrounding edge of the densely growing sand sedge, Carex arenaria, amongst which the prey was hunted.

T h e prey was paralysed, on two occasions not perfectly so.

It was observed that when being taken into the nest, the impaled fly was moving its abdomen rhythmically up and down. When being transported to the nest it was held rigid impaled upon the sting, which was inserted in the centre of the underside of the thorax, the insect always lying over to the right, head foremost and touching the wasp's abdomen.

Four specimens of the dipterous prey were taken from the nests, one in July, 1952 and three in July, 1955 and all were of the same species Thereva plebeia Linn.

T h e wasp which had its nest on the flat caught and transported five flies over the same route at various intervals during a period of 35 minutes, crawling down the leaf blades of the Sand Sedge and running, with occasional pauses, a distance of five feet over the almost barren sand : the other transported its prey by flight.

T h e nests were sealed with sand which was removed each time on arrival with the prey, and replaced by the wasp when leaving, but remained open during the short period of storing it. When the wasp entered, she rapidly removed the sand by scraping it away with the forefeet, the abdomen and impaled prey being slightly raised to allow the sand to pass freely under the b o d y :