'ilit MIGRATIONS OF INSECTS.
NOT long ago a story was current which sounds like the realisation of a collector's dream. A ship was crossing the Atlantic from the United States, and was followed by a number of butterflies of a large species called the "black- veined brown." The butterflies kept up with the ship, prob- ably alighting on it at night, and when the steamer drew near the Scilly Islands were still following it. Shortly after- wards thirteen of these American butterflies were said to have been caught in Cornwall, it was alleged by friends of an ento- mologist on board, who contrived to let them know by the earliest possible means that such distinguished strangers might be expected.
Whether the story is based on fact the writer knows not But there is good reason to think that butterflies do occasion- ally cross the sea, whether by choice or compulsion, and that they are not the only insects that do so. Others also travel great distances by land, or migrate to pastures new on ships, in trains, and among the feathers of birds. The unusual numbers of the Camberwell beauty butterfly seen two years ago on the South Coast were believed to have been blown across, or to have flown across with a fair wind, from France, whence also passengers on the Calais-Dover boats saw not long ago swarms of common white butterflies crossing the Channel. This is not in the least surprising. The large vanessas, such as the red admiral or Camber-- well beauty, fly swiftly and strongly. One came out to a Scotch boat going up Channel and accompanied it all the way to the Clyde. When Darwin was off the mouth of the Plata, and also off the Patagonian shore, the ship was often surrounded by insects. "One evening," he writes, "when we were ten miles from the Bay of St. Bias, vast numbers of butterflies, in bands or flocks of countless myriads, extended as far as the eye could range. More species than one were present, but the main number were very similar to the common English colitis edusa. Even by the aid of a telescope it was not possible to see a space free from butterflies. Some seamen cried out it was snowing butterflies."
There seems to be an occasional migration of insects into this country across the North Sea. Very few people who have lived on the coast of Norfolk or Suffolk doubt it. From time to time insects are found washed up by the waves, or floating near the shore, in numbers "like dust for multitude." It is possible that they were blown off-shore first, and then washed up again, by a change of wind. But it does not seem probable that they would be in such compact masses if dispersed and struggling against an adverse gale at some distance from land. On the other hand, it is well known that birds some- times fall into the sea from exhaustion when crossing towards land, and the case of these lady-birds seems much the same. Sometimes the drowned invaders consist of black flocks of the tiny turnip beetles, which lie on the waves like soot. Fishermen who spend much of their time off the mouth of the Wash and the North Norfolk coast have told the writer that butterflies constantly visit their boats, flying in front the sea; and from time to time blue butterflies are seen lying at short intervals, from yard to yard, along miles of the sea- fringe of sand on the Lincoln coast.
The painted lady butterfly appears to assemble for migra- tion as swallows do. Great columns of them many yards wide have been seen flying in a given direction. A locust alighted on the deck of the 'Beagle' at a distance of three hundred and seventy miles from land. If an insect only four inches long can make such a flight, no limits can be set to the possible migrations of locusts. They cross seas and even mountains. Some years ago they appeared near Dar- jeeling. Whence they came is not precisely known. But it is believed that they crossed the Himalayas from Thibet. The invasions of locusts are best remembered when for some reason unknown they decide to leave the regions over which their flight is generally taken, and to make a vast aerial trek into others. Such invasions naturally attract great attention. The records remain, emphasised by the actual losses inflicted, and not infrequently by more serious misfortunes. In the Middle Ages a locust invasion of the North or West was re- garded as one of the regular precursors of great pestilence,s. They are noted as among the forerunners of these great calamities. In 1528 there appeared in the Mark of Brandenburg, during the prevalence of a south-east wind
and a great drought, swarms of locusts, "as if this prog- nostic. too of great epidemics was not to be wanting," says Hecker. This " prognostic " had been observed before the Black Deathin the fourteenth century, the beginning of the morbific conditions" in the Far East having been innumer- able locust swarms, which destroyed the crops in Hunan, and caused the famine which pestilence followed. Locusts appeared in Franconia in incredible swarms in 1337, and the celebrated "stinking mists" which spread over Italy in 1348 were made worse by the odour of putrefying locusts, which had spread from the East to the West." The locusts were regarded as having been summoned by celestial wrath to complete the destruction of mankind which earthquake, famine, and pestilence had begun. In 1542 swarms of locusts migrated from the interior of Asia, and travelled across Europe, as far North as the Elbe, and as far South as Spain. The Turks were then invading Hungary, and by a natural coincidence brought the plague with them.
Induced migration of insects offers some curious points in political natural history. At the beginning of the last century the possibility of introducing the cochineal insect was much discussed in India. Red dye was ex- pensive and scarce ; but red was a colour highly prized and for which there was a great demand. Clearly if the cochineal could be introduced there would be a sale to a vast local population. The cultivation of the cactus on which it fed, and of the insects themselves, which are planted out in little communities on each young cactus- plant, seemed exactly suited for the laborious Hindoos. To add to the wealth of the many nations and languages of the peninsula by the induced migration of one hardy plant and a little red blight seemed almost a natural miracle, yet a possible one. Yet for some reason, though the economic argu- ments were all sound, the cochineal insect refused to migrate with a cheerful mind. It flourished when taken from its native Mexico to the Canary Islands, that Western foster- mother of other tropical products, and to some degree in Java and Algiers. But the parts of India to which it was taken did not suit it. On the other hand, an equally insignificant insect has crossed the Atlantic, and not only the Atlantic, but the New World itself, and been settled on the Pacific coast by the aid and desire of the Californian fruit-growers. The story of its journey and establishment is like an echo of some anecdote by Fferodotus of Greek rites rationalised by reference to some Egyptian "mystery." The ancients had an imme- morial custom of hanging up branches of a wild fig, which they called the goat fig, just as we speak of the " dog " rose, on the edible fig-trees at certain seasons, in the belief that the wild fig fertilised the other. In this they were perfectly right, but it was not done in the way in which they thought. Though the wild fig has male and female flowers, the former do not directly fertilise those of the edible fig. That is done by an insect hatched in the female blossom of the wild tree. These blossoms turn into galls, the galls in turn liberate a fly, the fly visits and is covered with the pollen of the wild fig, and then flies into the female flower of the other and fertilises it. In order that the edible figs introduced into California from Asia Minor might be properly fertilised these insects were introduced, it having been found that without them the trees did not give a proper yield.
A curious instance of insect migration in which the creature seems to have travelled in order either to "better itself," or because it is naturally of an adventurous turn, was given some years ago by a Russian diplomatist who in the intervals of political work applied himself to the task of unravelling the ancient and widespread belief that bees are born from the bodies of dead oxen. It is a belief of remote antiquity, which appears in many languages. The author identified it as a fly called Erystalis tenaz, which, in addition tor being very like a bee, has the power of feeding on and breeding in a very great number of substances, nice or nasty. In proof of this the author quoted evidence as to the curious migrations of the fly, which has in recent years accompanied ships into most quarters of the globe, and become a colonist, like the brown rat or the cockroach. The large Oriental cockroach is now firmly established in this country. In return for this doubtful blessing we have sent to New Zealand the humble- bee to fertilise the Antipodean clover, and are, it is said, about to export lady-birds to eat the blight on the vines of Australia.
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