THE AMERICAN ENTOMOLOGIST. 



ping of their wings was distinctly audible. They 

 hung in rows (often double) on the lower dead 

 branches, and in bunches on the needles. I find 

 by my note book that visiting the fiock towards 

 evening, it was receiving additions every moment. 

 I caught a net full off a bunch of dead needles, 

 and. walking away to some distance and letting 

 them go, all but three returned to the fiock. The 

 question as to where tliey came from seems a very 

 interesting one. I was told by Dr. A. W. Chap- 

 man that there was hardly milk-weed enough in 

 all Florida to produce one of these flocks, which 

 doubtless do not confine themselves to Apalachi- 

 cola. During my visit I found two more flocks 

 not far from the tirst, but neither of these was as 

 large. I should mention that I often observed 

 examples among them in coitu." 



The inference is legitimate from facts 

 like this that the pine forests of the more 

 southern States offer the most favorable 

 hibernating quarters for this butterfly, not- 

 withstanding the milk-weeds are scarce 

 throughout that country compared with 

 what they are in the more northern States. 

 Under the most favorable conditions there 

 is little doubt that the larger proportion of 



[Fig. 35.] , 



Clustering of Danais archippl:,s (after Tha.xter). 



the individuals comprising such swarms 

 perish before spring. The few pregnant 

 females that survive may be seen, faded 

 and often tattered, flying swiftly in the 

 spring in a northward or northwestward 

 direction over the prairie region of Te.xas, 

 Indian Territory, Kansas, etc., supplying 

 the milk-weeds here and there with eggs. 

 A fresh generation is produced in less than 

 a month, and these extend still further 

 north, until we find the species late in 

 summer away up in the Saskatchewan 

 country. In an article in the Scientific 

 American for April 6, 1878, in which these 



views were put forth, we concluded with 

 the following paragraph : 



"We can thus understand how there are two, 

 three, or more broods in southerly regions, but 

 only one toward British America. The excep- 

 tional flights noticed in the spring, and which, so 

 far as recorded, take place quite early and in the 

 same southerly direction, find a similar explana- 

 tion. They may be looked upon as continuations 

 of the autumn flights. Hibernating in the tem- 

 perate belt, the butterflies are awakened and 

 aroused upon the advent of spring, to find the 

 milk-weeds not yet started, and they instinctively 

 pass to more southern regions, where spring is 

 more advanced. In short, these migrations find 

 their readiest explanation in the instinct of the 

 species to lengthen the breeding season and to 

 extend its range; and the prevailing winds at 

 particular seasons are of a character to assist it. 

 There is a southward migration late in the grow- 

 ing season in congregated masses, and a north- 

 ward dispersion early in the season through 

 isolated individuals. It is a notable fact that the 

 two butterflies which most display this instinct, 

 namely, the species in question and the ' Painted 

 lady ' (Q'«//;/(7 cardiii), have the widest range of 

 known species. The last is cosmopolitan, occur- 

 ring in all quarters of the globe ; while our Ar- 

 chippus, originally confined to America, though 

 ranging from Canada to Bolivia, appears to be 

 following the milk-weeds wherever these are, 

 through chance or purpose, introduced. It has 

 lately spread over some of the islands of the 

 Pacific, to Queensland and New Guinea, and 

 over the Azores to Europe, such a spread neces- 

 sarily indicating great power of long-sustained 

 flight, since the milk-weeds are not plants of com- 

 mercial value, and it is highly improbable that 

 the species has been carried in any of the pre- 

 paratory states on ships." 



What is true of the Archippus butterfly 

 is largely true also of the large yellow but- 

 terfly, Calidryas eubule, which has a very 

 wide range, and the larva of which feeds 

 on different species of Cassia. Careful 

 observers in the Southern States have in- 

 sisted that this butterfly invariably moves 

 to the south or southeast in the Fall of the 

 year and just as invariably in the opposite 

 direction in the spring. So marked is this 

 in the case of eiibule that day after day the 

 insects may be seen flying by in a bee-line 

 which they pursue so persistently that, 

 rather than deviate to the right or left of a 

 building or other intervening obstacle, they 

 always pass over it though the flight is or- 

 dinarily quite low. 



The regular meetings of the Cambridge 

 Entomological Club for the next three 

 months are fixed on April 9, May 14 and 

 June II. The Club meets at 19 Pollen St., 

 Cambridge, Mass., at 7.45 p. m. 



