Lepidoptera of Sikkim. 275 
and in splendid condition, many species whose existence 
was a few years ago quite unexpected. But to the higher 
elevations, where they feel the cold much more than 
we do, they will not go willingly, or work half as well as 
they do below, and so it happened that on my first visit 
to Tonglo, a mountain 10,000 ft. high, on the Nepal 
frontier, and only twenty miles from Darjeeling, I took 
in great abundance several butterflies which had hitherto 
been thought extremely rare, and three which were 
undescribed, besides a great number of Heterocera 
which are quite unknown to Science. 
Again, as to the dates which are given for the 
occurrence of the different species, I may say that in 
the case of insects inhabiting the hot valleys below 
3000 ft., which form so large a proportion of the whole, 
the season begins early in March, when the first broods 
of many species begin to fly. During April and May 
the numbers of individuals and species increases to its 
maximum, and those species of Papilio and others which 
we believe to be single-brooded come out at this time. 
Occasional heavy rains commence in May, which about 
the 15th of June become much more continuous, lasting 
with almost daily bright intervals in the lower valleys ; 
but with only an hour or two of sunshine in the early 
morning, or rare breaks of a week or ten days of fine 
weather at the higher levels, until September or October. 
This, however, is the season when butterflies are com- 
paratively most numerous at the higher levels and less 
abundant in the hot valleys, but, though we cannot say 
so with certainty, we believe that an irregular succession 
of broods of most species appear throughout the rainy 
season, which at the close of the rains assume increased 
proportions; so that October is, next to April, the best 
month for collecting in the tropical zone. From October 
the number of species rapidly decreases till the end of 
the year, when a few only are found in the lowest valleys 
and outer hills. During January and February there is 
almost a cessation of butterfly-life, though even then 
some species can always be found on sunny days. 
But in dividing the year for entomological purposes in 
this part of the tropics we can define three seasons. 
First, the hot from March to June. Secondly, the wet 
season from June to October, when about 8-10ths of the 
annual rainfall occurs. This varies in Sikkim from about 
