MIGRATION AND DISPERSAL OF INSECTS ! LEPIDOPTERA. 188 



where it becomes exceedingly abundant in the autumn months. This 

 irregularity in abundance is equally marked in both species, 1868, 1871, 

 1892, and 1899 were among the abundant years for A. archippm. Moffat 

 says that near London, in Ontario, he has seen " specimens arrive in 

 the spring in a sorely faded condition, indicating age and exposure to 

 the weather, followed by others that were comparatively fresh as if 

 they were younger and less travel-stained than the first. Then, again, 

 the first arrivals are sometimes in fairly good condition, as if they had 

 not been long upon the wing ; whilst other specimens have been seen 

 haunting a particular locality for weeks, and, as far as could be judged 

 by their gradually fading colours, they were the same individuals." 

 He has also '•' seen them flying plentifully for six or eight days and 

 then begin to pair, indicating that these particular individuals had not 

 laid eggs before reaching that locality ;" further, he has " seen fresh- 

 looking specimens flying at the time the new brood was emerging from 

 the chrysalis, and so fresh as to give rise to a difterence of opinion as 

 to whether they were previous arrivals or bred on the spot." Lastly, 

 he had " seen quite small caterpillars on the milkweeds when others had 

 passed into the mature state," all of which has convinced him that 

 there is " more than one wave of migration northward during the 

 breeding season." All these irregularities of habit will be certain to 

 strike one who has studied the subject, as being readily paralleled 

 during a series of years by the immigrants of Coh'a>< fiium and 

 P^iramcia canhii, and their progeny in our own country. 



The species belongs essentially to the tropical and subtropical 

 regions of the American continent. It is found all over the West 

 Indies, as well as on the mainland, and extends south as far as 

 Patagonia. During the winter no specimens are seen above 30° N. 

 lat., in North America, and, at this latitude, but rarely; the only 

 individuals that appear to get through the winter seem to be those 

 that are well within the subtropical and tropical areas. The species 

 is most probably continuously-brooded in the most favourable districts 

 of its permanent winter home, and Edwards says that there are three 

 or more broods in a season in Virginia ; whilst in the more northerly 

 part of its summer range — Hudson Bay district, and the basin of the 

 Athabasca — one, and occasionally an attempt at a second, brood 

 appears to be its maximum. Moffat states that it is quite clear that 

 it cannot survive the winter in any stage of its existence in Ontario, 

 or northward of it, and that each recurring winter sweeps the country 

 clear of this particular species, and it has to be restocked every spring- 

 by immigrants from the south. Eiley suspected that fertile females 

 started northward in early spring, when the Asdcjiios was ready to re- 

 ceive their ova, and travelled some distance before they had finished 

 ovipositing, when these would naturally perish ; then he supposed 

 their progeny continued to advance and carry on the Avork of producing 

 ova to stock the milkweeds as they came north, so that there might 

 be several broods required in a season to reach the northern limits of 

 its food-plant. Scudder claims, on the other hand, that it is a long- 

 lived insect, that a female starting northwards may travel for weeks, 

 depositing her eggs as she goes, a few at a time, until she reaches the 

 northern limit of the growth of the food-plant, and further asserts that 

 the insect leaves its winter quarters later in the season than other 

 butterflies, that it is " single-brooded," that it " continues upon the 



