Some Habits of the Red-Legged Spider Hunting Wasp

SOME HABITS OF THE RED-LEGGED SPIDER HUNTING WASP EPISYRON RUFIPES, LINN by

HENRY J. THE

BOREHAM

HABITAT

species is only common in some suitable sandy habitats upon the Breckland heaths and in some years. In the July of 1952 it was fairly common on a small piece of heath which measured some twentv Square yards at West Stow. This was bare of Vegetation except for a few small isolated hummocks of ling and sand-sedge both intermixed with bents of the Sheep's Fescue-grass, which as a result of wind erosion remained above the surrounding small sea of grey sand. This particular area with its near surroundings was rising toward the west, and received the fßll rays of the sun ; in consequence the sand became extremely hot and dry. Here on the west side was a large and almost filled-in disused rabbit burrow where under the overhanging turf not less than four female Spider hunting wasps were storing their prey in the sand. It was ämongst the hummocks that the prey was hunted, the wasps' wings always in agitation as they proceeded from one hummock to another by intermittent short runs and flights. Once a spider had been discovered, the wasp's agitations became the more intense ; again ^nd again it would circle and climb on and into the grass at the base of the hummock, again descending and rapidly digging holes with its forefeet into the sand, the sand passing out under its abdomen in a continuous stream. But none of these holes appeared to be used for the storage of prey, and were probably dug from the sheer excitement and expectancy of a capture.

THIS

As all this tremendous excitement continued, the hunted spider would endeavour to conceal itself in the middle of the foliage where the wasps did not usually follow. If it succeeded in reaching such a position it remained frozen and had a fair chance of escaping.

After some hesitations the wasp would continue on its way, but it was not safe for the spider to remain as the wasp would surely return.

I T H E H U N T I N G AND CAPTURING OF

PREY

The prey appeared to be located and hunted by the wasp's sense of smell and when a capture was imminent the agitations of the wings and the running and digging were intensified to frantic proportions. The attacking wasp would approach the spider from any direction weaving its way with frequent hesitations and bewilderment through the semi-dried grass until it came within striking distance.

RED LEGGED SPIDER HUNTING WASP

45

When the final attack came the position was face to face ; the wasp quickly side-stepped and placed its forefeet upon the spider, and simultaneously held it in a position which was slightly to one side. T h e wasp curved its abdomen under the spider and quickly inserted its sting into the abdomen between each pair of legs separately ; thus the spider was paralysed by the injected poison.

The wasp now seized one of the spider's fore feet with its jaws, the leg was pulled straight and straddled, and the wasp then proceeded by short runs and attempted flights to drag its heavy bĂźrden towards the nest hole.

When the spider first sensed the wasp's presence it did make some efforts to escape, but these efforts were never carried to their possible conclusion. This was probably due to mesmerism, because the spider's movements became the more restricted as the wasp's agitations became intensified and as its movements narrowed to within striking distance the spider appeared to be completely mesmerised, with its legs withdrawn, and appeared to be dead. Thus it remained having made but a very feeble effort to defend itself. T h e spider sensed the presence of the wasp by the vibrations transmitted through the webs and foliage and its inborn instinct differentiated between the vibrations of a trapped fly in its web and those of the hunting Episyron rufipes.

THE

PREY

Six paralysed spiders of the same species belonging to the family Araneomorphae w'ere recovered from the sand at the rabbit burrow. They comprised five females and only one male. The male appeared to have been completely paralysed but all the females were able to withdraw their legs when pulled. After their abdomens had been fixed with the legs extended, they were able to move their palps together and their forelegs slowly up and down as objects were passed over them. Each had an ovum adhering to its back. After these ova had been removed, two spiders remained alive for four weeks and one which was slightly larger then the others remained alive for six weeks in this paralysed State.

REMARKS. The antennae were constantly waved and vibrated but it appeared unlikely that they assisted in locating prey apart from sensing obstacles and making measurements for the accurate insertion of the sting. The frequent hesitations and bewilderments of the wasp could only have been due to the temporary loss of the spider's spoor. Had the wasps hunted by sight these happenings would probably not have occurred so frequently.

This insect like the rest of the original Breckland fauna and flora has become very rare indeed during this last ten years, 1951-1961.