It seems pretty clear that this species passes the winter as a caterpillar, and from the evidence available it appears equally certain that the caterpillars would not survive an ordinary winter in this country. Possibly, however, in very mild winters, or in certain warm nooks on the south coast, some may be able to exist until the spring, and then complete their growth and reach the butterfly state. In such native-born butterflies the ancestral migratory habit may be lost, owing to climate, and they would not, therefore, wander far from the spot where they emerged from the chrysalis, but found a colony, which probably would be cleared off sooner or later by the severity of an English winter.
The Pale Clouded Yellow was not mentioned as an English butterfly until Lewin wrote about it in 1795. He states that he only met with it "in the Isle of Sheppey and on a hilly pasture-field near Ospringe in Kent." He seems to have noted it in different years at both places. Stephens, in 1827, referred to it as a rare British species, and from that date until 1867 it seems to have been common only in 1835, 1842, 1857, and 1858. In 1868 it was abundant in the southern and eastern counties, and was observed as far north as Lancashire and Yorkshire, also in Ireland. It was common on the south coast in 1872, and rather more so in 1875, when it spread into Essex and Suffolk, and also inland. Until 1875 the butterflies seem only to have been noticed in the autumnal months, but in that year specimens had been seen in May and June. In 1876 the species was pretty plentiful, but after that date it did not again occur in numbers until 1892, when it was recorded from most of the southern and eastern counties. In 1893 one or two specimens were reported as seen in April or May, but less than a dozen were recorded as captured during the autumn of that year. Not much was seen of the butterfly again until 1899, when a score or so were recorded from Kent. Two or three specimens were seen on the south coast in June, 1900, and the species was plentiful in the autumn of that year in many parts of the country. Single specimens were seen in June, 1901, and in the autumn the butterfly was again fairly common in several southern counties, and abundant in parts of Essex. In 1902 a male was taken near Dartford in March, and one example in May in a locality where two specimens had been captured on October 20 of the previous year; six males and one female were obtained between June 27 and July 12 at Sheerness. The summer of 1902 was a cold one, and, with the exception of four specimens at Folkestone in August, the species was not again seen during that year or the following one; but in 1904 a good many specimens were secured at Chatham in September, and one or two at Margate in August.
Pl. 20.
Pale Clouded Yellow Caterpillar.
(After Hübner.)
