Ch. VII ]

MIGRATIONS OF INSECTS.

87

alighted at Selbourne, spreading at the same time ingreat clouds all along the vale from Farnham to Alton.These aphides are sometimes accompanied by vastnumbers of the common lady-bird ( Coccinella septem-punctata), which feed upon them. *

It is remarkable, says Kirby, that many of the in-sects which are occasionally observed to emigrate, as,lor instance, the libellulse, coccinellse, carabi, cicadas,&c. are not usually social insects; but seem to congre-gate, like swallows, merely for the purpose of emi-gration. f Here, therefore, we have an example of aninstinct developing itself on certain rare emergencies,causing unsocial species to become gregarious, and toventure sometimes even to cross the ocean.

The armies of locusts which darken the air in Africa and traverse the globe from Turkey to our southerncounties in England, are well known to all. Whenthe western gales sweep over the Pampas, they bearalong with them myriads of insects of various kinds.As a proof of the manner in which species may bethus diffused, I may mention that when the Creolefrigate was lying in the outer roads off Buenos Ayres,in 1819, at the distance of six miles from the land,lier decks and rigging were suddenly covered withthousands of flies and grains of sand. The sides ofthe vessel had just received a fresh coat of paint, towhich the insects adhered in such numbers as to spotand disfigure the vessel, and to render it necessarypartially to renew the paint. £ Captain W. H. Smythwas obliged to repaint his vessel, the Adventure, in

* Kirby and Spence, vol. ii. p. 9. 1817. f Ibid. p. 12.

f I am indebted to Lieutenant Graves, R.N., for this inform-ation.