'59 IN THE SUN by W.
S.
GEORGE
THE sunny summer of 1959 produced ideal conditions for observations of butterflies and hover-flies. In the 212 days between March Ist and September 28th observations were made on 162 days, but the year was not, I found, notable for immigrant butterflies, two only Clouded Yellows (Colias croceus, Fourcroy), being seen on September 22nd and 27th at Aldeburgh, and no Painted Ladies (Vanessa cardui, L.), at all. Since all insects tend to migrate in the same years, I suspect that those hover-flies seen were resident flies. I was mainly impressed that many hover-flies appeared and vanished at certain periods whose dates tallied well with my scantier records of previous years. I find myself comparing them with the butterflies, whose similar seasonal appearances are connected with very strict breeding cycles : presumably, then, the hover-flies must also have such cycles. So little is known of their breeding habits that I find myself conjecturing. Only two species, Eristalis tenax, L. and E. aeneus, Scop., are known to hibernate as adults, a fact I can confirm. Both flies appeared on April 4th, our first hot sunny day, along with E. intricarius, L. and Chilosia grossa, Fallen. Are they hibernants also ? But seeing a " White " butterfly that day also (which is known to spend the winter as a chrysalis) shows that we cannot presume so. It has been suggested that the pretty orange Syrphus balteatus, Degeer, may hibernate as an adult fly, but I regularly first see it in early June, and would surely have seen so common and obvious a fly earlier if it had been about. It may perhaps migrate. How do the flies spend the winter ? This seems to me important. All British butterflies (except the non-Suffolcian Speckled Wood) must spend the winter in one stage particular to the species, egg, larva, pupa or adult, and I think the same may apply to many of our hover-flies. I record on April 23rd, 1959, the emergence of an unrecognisable limp, green fly, found crawling on a recently potted Primrose plant. Hardening to a brown and orange mature fly, this proved to be a female Melanostoma mellinum, L., which had probably wintered as a pupa, on or near the plant. The easily recognised, snouted, red fly Rhingia campestris, Meig., known to breed in cow dung, puzzled me this summer. The first brood, during May, was very abundant, visiting flowers of Primrose and Cranesbill not frequented by other hover-flies with shorter tongues. But the second brood, in August, were represented by occasional specimens only. Were they hit by the
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drought drying up the cow-pats, or do most of the larvae not mature tili the winter, nor pupate tili the spring ? My previous records suggest that this fly is never as common in August as in May, and many of our summers have been far from droughts ! However, the non-appearance of a species is no proof of its absence, for despite an abundance of the Peacock Butterfly (Nymphalis io, L.), in late July, they were very little in evidence during September, yet we know that these same butterflies will hibernate and be abundant next April. Probably the dry conditions did reduce the populations of the puddle-breeding Eristalis species, though E. arbustorum, L., was common in August and September. Despite the plagues of wasps, no extra numbers of their nest scavenging flies, Volucellapellucens, L., were in evidence. Perhaps resulting from the record scope in wasps' nests, they will be commoner in 1960. The black and yellow fly Syrphus corollae, Fab., appeared in great numbers in July as usual, hovering low among plants. Presumably, they depend upon aphids as larval food, as do their close relatives ; but I noticed no preference in each species of Syrphus for particular plants on which to hunt aphid colonies. I noted S. luniger, Meig., laying eggs on a greenfly-infested rosebush on September 6th. In 1958 I found Scaeva pyrastri, L., doing the same. Syrphus elegans, Harris, was common in May, then vanished, clearly a single brooded species, as is the less common S. albostriatus, Fall., in August. T h e following table shows hover-flies and butterflies whose seasons approximately coincide. Small Apl., Jun., Eristalis tenax, L. Tortoiseshell Aug. / Sept. E. aeneus, Scop. Peacock Apl., Aug. E. sepulchralis, L. Common Blue Jun. /July, Aug. Syritta pipiens, L. Small White All summer. Leucozona lucorum, L. Orange T i p May /June. Syrphus elegans, Harris. Orange T i p May/June. S. balteatus, Degeer. Red Admiral June onwards. S. albostriatus, Fall. Purple Hairstreak August. S. corollae, Fab. Gatekeeper July. Myiatropa florea, L. Meadow Brown Jun./July/Aug. Helophilus frutetorum, Fab. Green Hairstreak June. Merodon equestris, Fab. Green Hairstreak June. Platychirus manicatus, Meig. Wall May/Jun., Aug. Chiiosia illustrata, Harris White Admiral July/August. Clearly, much patient Observation and breeding work is needed to explain these facts.