Some Details of the Life and Habits of the Digger Wasp Metacrabro quadricinctus

46

SUFFOLK

LEPIDOPTERA

common. On 7th September however we took three very fresh White-point Wainscots (Leucania albipuncta Fabr.). On this date the Grey Pine Carpet (Thera obeliscata Hübn.) was very common and shewed every conceivable Variation. Düring August a number of the tiny Diamond-back moth (Plutella maculipennis Curt.) was seen. This insect was reported in countless numbers from the North-east coast and was thought to have been carried there by a favourable wind from Scandinavia.

Düring the early autumn all the Vanessas, except the Large Tortoiseshell, have been seen in Stowmarket in greater numbers than for several years, and it is to be hoped that before long we shall have this fine butterfly with us again in its former numbers.

SOME DETAILS OF THE LIFE AND HABITS OF THE DIGGER WASP METACRABRO By

QUADRICINCTUS HENRY J.

FAB.

BOREHAM

species was working in the butt-end of a fallen beech tree at Fornham Park, Bury St. Edmunds, from July to October, 1953.

T h e interior wood was decayed so that the wasps excavated their burrows and constructed their cells in any part of it. T h e exterior wood was extremely hard and therefore the wasps had to make their entrances at the broken and rotten root-ends and through the weathered cracks upon the surface.

THIS

Five females were seen during the second week in July, but the number gradually increased and remained at about 25-30, from the first week in August until the third week in September when the number decreased until only one remained on October 3rd.

THE

DIGGER

47

WASP

The length of the females was between 10mm. and 15mm., usually about 13mm.

EXCAVATION

OF

BURROWS

Each of three nesting holes was used by more than orte individual, the numbers seven, four and three. The entrance holes and main burrows measured 7mm. across, the excavating appeared to be carried out mainly at night and during spells of dull and cold weather, rarely in bright sunshine. The main burrow, used by the seven mentioned above, was 27 inches in length and continued deeper into the interior where the wood was harder.

Only two side burrows with cells were found in this length.

The main burrows of the solitary ones, varied in length from nine to 14 inches, the lateral ones were also of various lengths, each ending with a cell, which was sealed by the wasp Alling the entire length with excavated material. In one nest consisting of five cells four were examined ; these were sealed and contained four flies each, but no eggs could be found upon them.

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CfiL-lf.- ^ Catititunin f>y-<Lstvi In addition to the details shown in diagram, two other stored and sealed cells were found in different nests. One was stored with four Orthellia cornicina, the other with four Catabomba pyrastri.

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48

THE DIGGER WASP

M E T H O D OF C O N V E Y I N G AND STORING THE PREY

The hunting grounds were trunks of trees, logs and the foliage of eiders and brambles. The prey consisted of two-winged flies which were more or less paralysed before conveyance to the nest. Sometimes prey taken from them were able to move their legs, and on one occasion when the fly was released it was capable of running and Aying erratically for periods of some seconds duration. The wasp carried its prey the right way up, both in flight and when moving over a surface, by embracing it with its middle legs between the heacl and thorax. The fly appeared as if attached to a swivel which allowed it to respond when carried over a rough surface. The flies were packed tightly in the cells with their heads pointing away from the entrance. Where more than one wasp was using a main burrow, all returned after an absence of about 20 minutes, following each other with their prey at intervals of two or three minutes. Seidom would one be seen to leave before all had returned. Occasionally after depositing the prey one would loiter at the entrance while three or four passed in and out, the outgoing wasp allowing the incoming one, with or without prey, a free passage by squeezing against the side of the burrow.

HOMING

The homing instinct of this wasp was fairly accurate. It appeared to have a habit of alighting some distance from the nest hole, sometimes only a few inches, occasionally a yard or more especially where nettles and the branches of eider shrubs were overhanging the nest holes. Some alighted with their prey on the foliage of these. After a short rest they would leave, but appeared to have lost their sense of direction, and again returned to the foliage, repeating this once or twice before alighting three or four inches away from the nest hole, and then approaching it as if uncertain of its position. After resting upon the foliage, the wasp appeared to have some difficulty in adjusting its prey for further flight, but at no time did it release the fly from its grasp.

THE

LARVA, P U P A A N D

COCOON

T h e following is a description of an almost mature larva : length 12 mm., legless and glossy, head translucent light brown ; mandibles black. Ist Segment translucent white, 2nd to lOth translucent bluish-white ; 1 Ith (anal) segment translucent white.

Extending along the dorsum from the 2nd to the lOth segment were two dark bluish subcutaneous lines 2 mm. apart, the colour

THE DIGGER WASP

49

fading at either end. This larva pupated without making a cocoon.

The cocoons were not clean and had the remains of flies, sometimes whole flies adhering to them. It would thus appear that the cells were stocked with more prey than was required by the issuing larva to reach its pupation. Three cocoons were of a light brown colour, and were made of a tough paper-like substance, each measured 11 mm. in length, another was 8 mm. in length and was at first translucent white. After two days it changed to an obscure greyish colour and the pupa became invisible, and turned eventually to a light brown.

THE

PREY

The following species of diptera were taken from the wasps upon their arrival at the nest holes.

SYRPHIDAE. Syrphus luriger (Mg.), Syrphus balteatus (Deg.), Catabomba pyrastri (L.). CALLIPHORIDAE. Sarcophaga carnaria (L.), Calliphora erythrocephala (Mg.). MUSCIDAE. Orthellia cornicina (F.), Dasyphora cyanella (Mg.), Lyperosia irritans (L.), Phaonia erratica (Fall.), Fannia fusula (Fall.), Polietes lardaria (F.), Mydaea scutellaris R-D.

A DESTROYER OF NESTS

In August two nests, each made by a single wasp, were marked for the purpose of collecting some cocoons at a later date. DĂźring the last week of October these two nests were opened when, to my surprise, they were found to have been robbed of their contents; only dust-like portions of flies and wood debris remained.

Both the burrows and cells were infested with wood-lice, Oniscus asellus Linn. So well had they feasted that not a particle of any cocoon remained.

A TROUBLESOME

PARASITE

A species of fly was continually loitering around, but did not enter the nest holes. It moved about upon the wood and when it found a nest hole it moved leisurely around, occasionally peering in. These movements lasted for a few minutes before it moved on again, only occasionally taking a short flight and returning to almost the same spot. It appeared ferocious towards all other flies and attacked and drove them off at every approach.

Only once was one observed to place an egg at the edge of an entrance hole about 2 mm. up the side.

7

50

THE DIGGER WASP

The wasps appeared unperturbed by their presence and seldom attempted to capture them.

On one occasion one was basking in the sunshine with its head level with the bottom of an entrance hole when a wasp emerged. The wasp immediately grasped it with its forelegs and both struggled in the air. Then it released the fly and continued on its way. T h e fly, apparently unharmed, returned to its previous position.

About seven of these parasitic flies Eustalomyia festiva (Zett.) frequented this habitat and their decrease appeared to correspond with that of the wasps, the last one Seen was on October 12th.

Observation was continued at this habitat in 1954. It was obvious that the persistency of the dull and rainy weather throughout the summer greatly curtailed their activities. The first female was seen on June 20th. None was observed carrying its prey until July 1 Ith, on which date three Eustalomyia festiva were present, on the 1 Ith and 24th activity was at its highest; all had ceased on August 28th. On August Ist, for some unknown reason, some of the prey was abandoned and was subsequently identified as the fly Delia cilicrura Rond. (=florilega Zett.) by Dr. C. D. Day and confirmed by Mr. E. A. Fonseca.

It was with horror that I viewed this habitat in June, 1955, to find that it had been completely destroyed by troops.

NOTE. Seguy in Faune de France [Dipteres Anthomyides] writes of Eustalomyia :â&#x20AC;&#x201D;" The larvae live in the nests of Crabro, where they devour the provisions stored by the wasps. The adults are often found on the trunks of trees, chieflyon those which present holes which serve for nests of Crabros. One also finds the flies on flowers."

My thanks are due to my friend, Dr. C. D. Day, for his identification of the Wasp, the Parasitic fly and the translation of the paragraph from Seguy.

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