White-mouthed Digger-Wasp

A REVIEW OF BRITISH

MACRO-LEPIDOPTERA

181

(.B. perla).

Nor was this all for this amazing season. T h e Ni moth (Plusia ni) was seen in unusual numbers in the south-west being taken right up to North Wales and Lancashire. Another' most remarkable occurrence was an apparent invasion of that splendid insect, the Oleander Hawk (Daphms nerii), a denizen ol tropical regions. Probably quite a dozen were captured chieny in the south, but one was captured in Carlisle This was a record year for this species. T h e Convolvulus Hawk (Herse convolvuli) and the Death's Head (.Acherontia atrofios) were comparatively scarce.

T h e autumn proper turned out to be one of the mildest in recent years. Butterflies consequently thrived. T h e Small Copper (Heod.es phloeas) was on the wing in the west well into November. T h e Brimstone (Gonepteryx rhamni) was seen in December while Peacocks and Small Tortoiseshells were still on the move at Christmas. It was also an exceptionally good penod for moths, nearly all the usual autumn species appearing in very good numbers. Most noteworthy among the less frequent ones were the Figure of Eight (EpĂźema caeruleocephala), the Sprawler (Brachionycha sphinx), the December moth (Poecilocampa popuh) and the Plumed Prominent (Ptilophora plumigera).

1 his last species was quite abundant in its restricted haunts in the south. This p e n o d saw several abnormal emergences A ew specimens of the Quaker (Orthosia stabilis), the Small Quaker (O. cruda) and even one of the Oak Beauty (Boarmia strataria) were recorded in December, three months before their usual time or appearance in March. , 19 „ 53 .can well be regarded as a memorable and fruitful year tor British Lepidoptera.

THE WHITE-MOUTHED DIGGER WASP Coelocrabro leucostomus Linn.

SOME

OBSERVATIONS

ON

ITS

LIFE

AND

HABITS

THE following observations were made by me on the life and habits of this species of Digger Wasp during the months of June July, August, September and October, 1951-52, at nests in a decaying railroad sleeper, Bury St. Edmunds, and in rotten willow tree trunks at West Stow Sewage Farm.

D I G G I N G AND EXCAVATION OF

NESTS.

This species of Digger in some cases is not truly solitarv and is so only up to the excavating of and storing their cells with Hies, laying their eggs thereon and sealing it up

182

THE WHITE-MOUTHED DIGGER WASP

I estimated that seventeen females were using the same entrance hole to nest in this railroad sleeper * and I observed when excavations were taking place the chewed wood was not brought to the entrance, but dropped and pushed behind the wasp as it worked, making its cell or lengthening the common burrow ; the whole length became blocked with the excavations. When the required extensions had been made, the wasp would then push the excavations out of the burrow in an almost continuous stream, this being done sometimes by using its head but mostly by using its tail. Whilst this was taking place other wasps would arrive at the entrance carrying their paralysed prey. On findine the entrance blocked, they would hover in front ot it tor a moment or two and then fly away and appeared to know exactly at what time to return. This they would sometimes do just as the entrance was cleared. I have seen wasps on completing this task squeeze themselves against the side of the burrow to allow the incoming wasps with their prey a free passage. I his move was made on every occasion that two met at the entrance When extending the nest, they often broke into completed cells T h i s was shown in the chitinous remains and sometimes the whole bodies of freshly paralysed flies which were pushed out during these extensions. Cocoons appeared to be untouched, as I saw no whole or part of any in the outcast excavations.

These wasps work at their excavating at any time ot day or night, the weather being of no account. T h e length of workings in the railroad sleeper, from the entrance u p to the last completed cell, measured 11J inches. In the first week of October I observed that all their activities had ceased. I then cut 15 inches off the end of the sleeper and split it open to investigate the workings • and what a maze to behold ! T h e wood was honeycombed with cells and burrows. T h e cells were all lying lengthwise pointing towards the entrance. No individual wasp's workings could be traced—all appeared as if they belonged to some social and organized colony.

ITS PREY

I have watched them bringing and have taken the following species of flies f r o m them on their arrival at nest holes 1 hey were : a small shining green fly (Microchrysa pohta L.), a small shining black fly {Microchrysa cyaneiventns Zett.); two each ot the following were found on separate occasions lymg outside the entrance hole—the Hover-fly (Sphaerophoria scripta L.) and the larvae of some species of fly.

T h e fly Michrochrysa polita L . was the chief species upon which they preyed. W h e n the nest was broken open, all but three cells were or had been stored with this species. I could find only * T h e railroad sleeper was not in use as such, but was built in the side of a bay used for storing coal.

THE WHITE-MOUTHED DIGGER WASP

183 two which had been stored with the species Microchrysa cyaneiventris Zett.* I found no cells which had been stored with these two species mixed. One cell was found stored with two species of Hover-flies; one of them was Sphaerophoria scripta L., the other I was unable to identify. There is no doubt that the larvae of flies found outside the nest hole had been paralysed, as they remained in the position where they had been left, in perfect condition, for three or four days, and then only to be washed away by heavy rain. The wasps continue to capture and carry flies to the nest during dull and light rainy weather, ceasing to do so only when rain is heavy and prolonged.

HOMING.

The homing instinct of this wasp is most remarkably accurate.

They never hesitate in front of the nest hole, butflydirect into it and quickly disappear, and because of this accuracy I was unable to observe how they carried their prey. It also gave me a difficult task in robbing them of their prey.

MATING AND PAIRING.

No males were observed loitering in the vicinity of nests.

COCOONS AND PUPAE.

The cocoons were generally of a light brown colour. Three which I found were of a much darker shade. They are clean and smooth without the chitinous remains offliesadhering to them, except for one end, where particles are attached. This end is very hard and is always found at the end of the cell which has been sealed and pointing towards the main exit. They are made of a parchment-like substance, easily pierced with a pin but not easily torn apart when double. Out of six specimens takenfivemeasured 10 mm. and one 11 mm. In November, I opened three cocoons and found that the pupa was white to pale yellow, except for the tips of the mandibles, which were black.

These and nine segments on the back were the only features which could be clearly recognised. These pupae measured 5 mm. In some cells a dark green mould could be seen and had in some spread over the cocoons.

In each of three cells I found two cocoons, a large and small.

These measured 10 mm. and 6 mm. Their position in cells was alongside each other, the smaller lying to the side farthest *Microchrysa cyaneiventris Zett and Sphaerophoria scripta L. are not recorded in the list of prey given by HAMM & RICHARDS in their paper on the Biology of British Crabronidae, Trans. Ent. Soc., London, 1926, Pt. II, pages 309-10, 323-24.

Microchrysa cyaneiventris Zett. appears to be very rare in SuffbLk, only two records are given in The Diptera of Suffolk. Family XV : Stratiomyidae. Compiled by Claude Morley. Trans. S.N.S., Vol. VII, Pt. I, 1949, page 14.

184

THE WHITE-MOUTHED DIGGER WASP _

away from the burrow and at a slight angle so that the tips were almost touching at the exit end. The measurements of these cocoons reveal that they contained male and female pupae.

It appears that these cells were used twice, probably by the same females.

The answer is, I believe, as follows : after the first stock of flies stored in the cell had been consumed and the larva having made its cocoon and following a short interval, the cells were re-opened and enlarged (see Excavations, p. 181), re-stocked with flies, another egg laid and hatched, and the result is male and female cocoons in the same cell. The smaller male cocoons in each case appeared from their position in the cells to have been the first ones completed.

I kept a piece of wood containing complete nests ; the conditions under which this was kept were warm and dry. (These conditions are not natural to this species of wasp, its nests usually being made in situations which are constantly damp and at times they become waterlogged with continuous rain.) These unusual conditions may be the reason for the following emergence.

I found that two females were the first to emerge from their cocoons during the second week of May, the third and last female on the 19th of May, the first male did not appear until the 28th of May. Males continued to emerge at intervals until the Ist of July, the total to emerge being 3 females and 11 mal es.

E V O L U T I O N — H o w W I L L IT EVOLVE ?

Having described how this species works together in excavating the main burrows, thus forming in some respects a colony, I have also watched others of this species which I found to be truly solitary in all their habits—this in particular in some rotten willow tree trunks at West Stow Sewage Farm.

MEASUREMENTS OF ADULTS.

Males. Of 13 specimens, 12 measured 6 mm., one 7 mm.

Females. 20 specimens. All measured 9 mm.

PARASITES.

Also forthcoming out of the piece of wood containing complete nests during the second and third weeks of May were two small flies and a small ruby-tailed wasp, another small ruby-tailed wasp of the same species appearing during the last week in June.

The flies were of a species belonging to the Larvaevoridae (=Tachinidae) and measured 4 mm. and 5 mm. approximately.

When and how these flies and wasps lay their eggs upon the host's prey is open for further observations, but I am certain through the hours of my observations that they did not loiter near or enter the nests during daylight.

THE WHITE-MOUTHED DIGGER WASP ACTIVITIES CURTAILED BY WEATHER,

185

1952.

T h e unsettled weather which set in on the 12th of July and contmued for the rest of the year brought a sudden and early end to the activities of this wasp. T h e y made three attempts to continue their work between the 12th and 18th of July, but each time they were overcome by the cold winds. This' was shown in the evenings when I observed one or two crawling about and was able to pick them up. T h e y eventually succumbed to this weather and none were observed after the 18th.

HENRY J .

BOREHAM.

MOUSE RESEARCH IN SUFFOLK ALTHOUGH the house-mouse (Mus musculus L.) is one of the best known mammals in the world, surprisingly Iittle is known about lts habits.

Volumes have been written about laboratory strains used for physiological experiments, but until the outbreak of war in 1939, the wild mouse received almost no attention in this country. T h e n it became clear that large stocks of c o m and flour would have to be held for long periods, often in makeshift buildmgs from which mice could not be efficiently kept out.

T h e rapid increase in numbers of mice living in these stores became alarming, and damage to ricks also became a problem of national importance.

Throughout the war biological research on the mouse, and on the brown and ship rats, was carried out by the Bureau of Animal Population, but after 1945 this work was taken over by the Infestation Control Division of the Ministry of Agriculture and Fisheries.

Members of the Society may be interested to learn that the Ministry's mouse research is partly being carried out at Rougham near Bury St. E d m u n d s in an ex-R.A.F. building. These buildings erected in East Anglia for the services have been put to some odd uses since the war, but surely one of the queerest conversions has been this development of a building designed for the training of bomber pilots into an official residence for a colony of wild house mice. Here the mice can be watched without disturbing them and information about their innate behaviour is being gained which may assist in designing intelligent control measures.

T h e structure contains a ground floor room 20 feet square and fifteen feet high, in which the mice are allowed to roam about freely, and an upper room, fitted with Observation holes in the