BUTTERFLIES OF THE DISTRICT OF COLUMBIA 121 



leaves, finally perching on its summit and then slowly walking about 

 and depositing the eggs. This process has been several times de- 

 scribed. Only a very few eggs are deposited on a single plant. I 

 have seen a female flutter about a small isolated wild cherry growing 

 in an open field, hitting the leaves, drawing away, and then hitting 

 the leaves again, finally perching on its summit just as if it had been 

 a milkweed. She flew off, however, without depositing any eggs. 

 The wild cherry projected for about a foot above the grass tops and 

 from a little distance much resembled a milkweed. 



This butterfl}^ has been reported flying about electric lights at 

 night. 



Flocking and migration. — The milkweed butterfly is especially re- 

 markable for its habit of gathering in enormous loose straggling 

 flocks late in summer or early in autumn and migrating southward, 

 and also for its habit of swarming in incredible numbers on the 

 twigs and branches of trees and bushes. In some places the trees 

 frequented by these insects in the swarming season have come to be 

 known as " butterfly trees." But so far as known it does not migrate 

 across the District, and at the present time it is not sufficiently numer- 

 ous to swarm. 



As an illustration of these phenomena the following observations 

 from near-by Maryland are of interest ; the quotation is from a let- 

 ter from Dr. M. G. Ellzey, of Washington, written on January 20, 

 1887 (Insect Life, vol. 1, no. 7, p. 221, January, 1889), and the events 

 described took place in 1886 : 



About 7 o'clock in the morning niy son, G. Murray Ellzey, called the attention 

 of myself and several other gentlemen to the fact that " the whole heavens 

 were swarming with butterflies." There were an innumerable multitude of 

 them at all heights from, say, 100 feet to a height beyond the range of vision, 

 except by the aid of a glass. They were Hying due southward in the face of a 

 stiff breeze. Observations upon the flight of individuals between points of 

 known distances apart showed that the rate of movement was not far from 

 20 miles per hour. Where they originally came from or whither they went we 

 could not tell. They undoubtedly came from beyond the bay, which, in that 

 place, is 14 miles across, and they must have been early on the wing. By 11.30 

 o'clock the numbers had declined, and it was evident the bulk of the flight was 

 over, but for several days a great many individuals, evidently following the 

 migratory movement, were observed. 



My brother-in-law, Mr. Daniel Murray, who had been three days previously, 

 viz., on the 20th of September, at Long Green, in Baltimore County, Md., saw a 

 vast multitude of the same butterflies in migratory movement ; they were seem- 

 ingly exhausted in flight and settled on the trees in such multitudes as to give 

 them the appearance of an autumnal forest. I was surprised at the great power 

 of sustained flight exhibited, also at the great distance an individual butterfly 

 could be seen by the unaided eye, at least across the water — not less than 1^^ 

 miles. 



Doctor Fox mentioned (Proc. Ent. Soc. Washington, vol 1, no. 4, 

 p. 207, 1890) having seen a large number of butterflies of this species 



