24 
MIGRATION 
as to overwhelm everything with which their prodigious 
numbers come in contact. 
It is in comparatively recent times only that the sudden 
appearance of certain kinds of butterflies and moths in this 
country is known to be solely due to immigration. During 
the middle of last century, various hypotheses to account for 
such visitations were put forward. The older authors sug¬ 
gested that the eggs of certain species, like the seeds of some 
vegetables, might “ occasionally lie dormant for several seasons, 
and not hatch until some extraordinary but undiscovered 
coincidences wake them into active life.” 
I he migration of butterflies is a common phenomenon 
practically throughout the world, but is much more frequent 
in certain parts than in others. There is also great diversity 
in the numbers of individuals. The swarms are sometimes 
so vast as to obliterate the sun and may occupy weeks in 
passing over the country. 
Among the British butterflies, eleven out of the sixty-eight 
species may be classed as migrants, viz. the Milkweed, 
Camberwell Beauty, Painted Lady, Red Admiral, Bath White, 
Large White, Small White, Clouded Yellow, Pale Clouded 
Yellow, Queen of Spain Fritillary, Long-tailed Blue. Two 
others which sometimes reinforce our indigenous species are 
the Small Tortoiseshell and the Green-veined White. Other 
species have been recorded as seen flying in from the sea, but 
there appears some doubt whether they were actually migrating 
to this country, or, what is more likely, individuals that may 
have flown out to sea either voluntarily, or had been carried 
out by strong wind and were making a return flight to land. 
I think the latter is more probable, especially in the case of 
the Small Heath and Meadow Brown ; both are apparently 
non-migrants. 
It has often been a doubtful question whether butterflies 
are capable of such long distance flights from one country to 
another. Particularly does this question arise in regard to 
the Milkweed Butterfly and its flight over the Atlantic from 
North America to the British coast, a feat which, without a 
shadow of doubt, it at times accomplishes. It must be 
remembered that butterflies while on migration have often 
been seen to settle on the surface of the sea, and after a short 
