Movement of White Butterflies

THE FIELD DIGGER WASP

193

It was interesting to observe that the two species of Lonchaeidae were the smallest species of flies, 5 and 6 mm. in length which I have taken from M. arvensis. This female M. arvensis was also smaller than usual and measured 10 mm. in length. The entrance hole of her nest was also smaller than the average, and measured only 5 mm. across. The length of life of the recovered paralysed flies averaged four days.

REMARKS

A. H. Hamm and O. W. Richards in their paper " The Biology of the British Fossorial Wasps "* illustrate on page 97 six females of M. arvensis, photographed after death, still gripping their prey by the proboscis. Nothing is stated as to how these specimens met their death or how likely they were to remain in this attitude.

I have a specimen in just such an attitude ; it is gripping the Blow Fly Calliphora vomitoria by the proboscis. Its death was caused by a stinging blow from a stick while it was in flight. The sudden impact probably produced a stimulus on the sensory nerves from which they were unable to relax at death. The blow caused a Splitting of the mesonotum at and over the joining of one wing ; no other outward injury could be seen.

From a long experience of observing the habits of M. arvensis I have found that many of them, after having been smitten down two or more times with the open hand, were reluctant to release their grip upon the prey ; this was strongly marked on the days when a cold breeze was blowing. When cold weather is continuous, death usually comes before the work to ensure the future of the species is completed, and through the tenacious habits of M. arvensis it is possible that some may die in the attitude described.

BIBLIOGRAPHY

* Hamm and Richards. Trans. R. Ent. Soc. Lond. 30th June, 1930.

Boreham, H. J. (1953). T h e White-mouthed Digger Wasp Coelocrabro leucostomus Linn. Some observations on the Life and Habits. Trans.

Suffolk Nat. Soc. 8, 181.

MOVEMENT OF WHITE by

S.

BUTTERFLIES

BEAUFOY

are several indications that in Great Britain in the Spring a northerly movement of Whites takes place (Large White, Pieris brassicae, L. ; Small White, P. rapae, L. ; Green-veined White, P- napi, L.) ; while a southerly movement can be observed in late Autumn.

THERE

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WHITE BUTTERFLIES

On Ist, 3rd and 4th September, 1962, my wife, daughter and I were watching cricket on the County ground at Worcester, and a number of Whites were seen Aying across the ground ; a record of the approximate directions of the flights was made throughout those days. It was not possible to identify all the insects, as some were too far away ; those that flew near enough were either Large Whites or Small Whites. No Green-veined Whites were identified, but there may have been a few of this species.

T h e weather was warm during the three days of Observation, and there was a slight, south-westerly breeze. On Ist September, there were long, sunny periods ; on the 3rd it was cloudy ; and on the 4th there were several heavy showers. T h e total numbers of the butterflies Aying are shown in the following table. We were very interested to note than the direction of Aight of each insect, during its passage across the fleld, deviated little from a straight line.

Direction N. N.E. E S.E. S. S.W.

w.

N.W.

Number of butterflies 10 8 23 60 22 35 62 10

If we ignore those Aying due East or due West, there were 117 Aying South of the East-West line and 28 Aying North of the EastWest line. These flgures show a significant difference, indicating that there was a deflnite movement from north to south. Again, if we ignore those Aying due North or South, those Aying East of the North-South line total 97 against 107 Aying West of the North-South line. This difference, however, is not signiflcant, and could be the result of chance.

Observation of the movement of butterAies is not easy as there are often obstacles in the way which may have some influence on the direction of Aight over short distances. Observation is also time-consuming ; but entomologists who also watch cricket matches can make valuable contributions in this way—the observations extend over several hours, the general direction of Aight can be accurately judged, and there is a large, unobstructed area over which the insects Ay.