MIGRATION AND DISPEESAL OF INSECTS : LEPIDOPTERA. 323 



viduals captured, when again, for many years the species will totally 

 disappear. That many of the species that occur thus capriciously 

 migrate, is well known. We have already [ante, p. 321) noted the 

 capture of several Achemntia atrojins far from land, but a much more 

 powerful insect on the wing than the last is Sjihin.r mnrulnili, and the 

 uncertainty of its appearance in Britain has long puzzled those inte- 

 rested in such matters. In some years, this species abounds in the 

 gardens of southern England, its long proboscis (several inches in 

 length) thrust deep into the nectary of the tobacco plant {Xlcotiana 

 a/linis), petunia, &c. Yet the uncertainty in its appearance does not 

 seem difficult to explain. In its more southern home (in northern 

 Africa) the moth emerges from the chrysalis in May. It at once lays 

 its eggs, which soon hatch, the larvai pupating in July, and giving 

 rise to a second brood of moths in the following month. These lay 

 eggs, and in the sunnier climes of the Mediterranean shores, the cater- 

 pillars feed up, and change to pupie in the autumn, the moths not 

 emerging until the following spring. If a few migrants of the spring 

 brood reach our shores, they lay their eggs in the ordinary course. 

 The larvaB which hatch from these find our summer quite hot enough 

 and, accordingly, they feed up, pupate, and, in the autumn, produce a 

 second brood of imagines, just as would have been the case if the eggs 

 had been laid in the more southern home of the insect, the only 

 diiierence being that they take a week or two longer over their develop- 

 ment here than they would have taken there. The progeny of this 

 brood is, however, usually unable to reach the chrysalis stage before 

 our winter is upon them, the caterpillars are killed by the cold, and 

 thus the species is prevented from taking up a permanent abode 

 among us. This was proved clearly by Poulton, who, rearing this 

 latter brood in confinement, and under especially favourable artificial 

 conditions, did not succeed in getting pupte until winter had arrived. 



Closely resembling this species in the uncertainty of its appearance 

 and in its inabihty to make a permanent home in Britain, is the power- 

 fully winged JJeilcjiJnla (/alii. This insect is, however, not double- 

 brooded. The moths emerge in June, the migratory instinct leads 

 them, in certain years, at once to spread abroad and they occasionally 

 reach our shores. In the summers of 1855 and 1H59 the moth 

 abounded in a few localities in England, but from the latter year, 

 until 1870, hardly a single specimen was noticed. In the latter year 

 the moths suddenly appeared in surprising numbers in June, and, in 

 the autumn, all our long stretches of sandhills, where the bedstraw 

 {(ialiinii) grows luxuriantly, were covered with the larviu. Hundreds 

 were captured, and hundreds — nay, thousands — must have escaped, 

 for thousands of acres of suitable ground were never searched. From 

 those captured, and afterwards reared artificially through the autumn 

 and winter, many moths were bred during the early part of the next 

 year, but whilst they thus survived under artificial conditions, there 

 was no reliable record of the occurrence of even a single specimen at 

 large for that year, thus proving conclusively the inability of the pupie 

 of this moth to stand our winter climate. From 1870 until 1888 there 

 was scarcely a whisper of the capture of a ]>ritish specimen of this 

 species, but, in July of the latter year, the inuigines again suddenly 

 appeared in considerable numbers, and the caterpillars were found in 

 the greatest profusion a few weeks later, as they had been on previous 



