INSECTS The geographical position of Cornwall does not appear to have so much influence on its insect population as upon its marine life and its birds. In common with the other southern counties of England, it possesses a number of insects with a very limited range to the north, but neither in wealth of species nor in pride of peculiar possession is it greatly distinguished from the adjoining counties. The width of the Channel no doubt diminishes the number of casual but exciting visitors from the Continent, though at Falmouth, Penzance, and occasionally elsewhere aliens ' of assisted passage ' are taken from time to time. There is evidence now and again of immigration on the south coast sometimes on an extended scale, but migratory movements seem to be much more frequent on the Bristol Channel side. At Bude, Mawgan Forth, Hayle, and elsewhere on the north coast a long fringe of black scum has been occasionally observed on the advance water of the inflowing tide or else a crape-like band on the sand at high-water mark, which on examination is found to consist of millions of drowned insects, presumably overtaken by adverse weather when en route, or blown out to sea by sudden storm. At Chapel Forth, St. Agnes, and at Mawgan Forth in the vale of Lanherne, an irregular stream of insects has been occasionally observed for hours at a stretch passing steadily out to sea, some- times in large flocks, sometimes in twos and threes, never showing undignified haste, but rarely loitering much before their departure. When cabbage whites are abundant this emigration stream becomes very conspicuous, and hundreds of thousands of these butterflies must at times in the course of a single after- noon pass out of the county to the north at Chapel Forth. As drowned butter- flies have never been reported in quantity along the north coast, it would appear that most of them effect a landing somewhere. There is little direct evidence to show that immigrant swarms come in on the Bristol Channel coast, but the number of waifs and strays from more northern localities, especially among the Lepidoptera, that are from time to time captured in Cornwall, certainly suggests movements of this kind. The remarkably genial climate of Cornwall might have been expected to favour the presence of a few specially southern insects, particularly round the head of Mount's Bay, but so far as known there are none peculiar to the district, and, indeed, the specially Cornish insects favour the north coast rather than the south, and the most obvious effect of the mild winters is to disturb the rest of hibernating species and hasten the appearance of some that emerge in the early spring. In some orders, and notably in the Lepidoptera and Coleoptera there is a marked scarcity of insects throughout the county, and the number of species recorded is no index to the density of insect population. In both the orders named a much greater proportion of species than usual is represented by only one or two specimens, and if these casuals were removed from the lists there would be a very considerable shrinkage in their dimensions. 163
