ACADEMY OF SCIENCES. 14y 
or other parasitic insects which might be present, imagining that so large an as- 
semblage of larvee would prove for them a certain attraction, but I did not suc- 
~ ceed in taking a single specimen, nor as yet have any appeared among the cater- 
pillars which I brought home with me. Ihave, however, observed in my 
breeding boxes four examples of a rather large dipterous parasite, probably of 
the genus Tachina. As, however, I carried away with me nearly ninety cater- 
pillars, all of which passed successfully into the chrysalis state, this is but a 
very small proportion to be aftected with parasitic enemies. Is it possible 
that this comparative immunity is owing to the sharp and formidable looking 
spines with which the caterpillars are furnished? Certain it is that the Van- 
essce generally are more exempt from the attacks of Ichneumons than most 
other butterflies. 
During the last summer, the young lupines in the Golden Gate Park were 
attacked by myriads of caterpillars, which at one time threatened their destruc- 
tion, but the preservation of the small birds in and about the park kept down 
the swarm, and a succession of very cold winds, during the middle period of 
their growth, killed them off in thousands. I raised from the caterpillars, of 
which I took away with me upwards of a hundred, no less than eighty-five 
specimens of Pyrameis Cardui aud Pyrameis Huntera, and not a single one 
among them was observed by me to be attacked by parasites. This, in con- 
junction with the facts noted above, with reference to Vanessa Californica, 
would seem to indicate that these insects enjoy a freedom from the assaults of 
their tiny foes, which is not granted to other members of their tribe. It may 
partially account for the vast swarms of the various species which periodically 
make their appearance in different parts of the world. But this is one of those 
singular occurrences connected with insect life, which are so difficult to ex- 
plain satisfactorily. The canon in which Vanessa Californica was found has 
been visited by J. Behrens and myself at least twice every season for the last 
six years, and though I have invariably sought most diligently for caterpillars, 
until now that of the present species has been utterly unknown to me. 
It may with almost certainty be predicted that the coming fall will witness 
the same large swarms of this butterfly as those observed by Dr. Behr in 1856 
and 1866, which dates will serve to indicate that the insect appears in such 
numbers about once in nine or ten years. The caterpillars collected by me fed 
voraciously, and changed into the chrysalis state from the eleventh to the 
twenty-fourth of the month, the transformation of all I had secured being 
complete by the latter date. In this condition, they were extremely restless, 
constantly keeping up a jerking motion, and knocking themselves against the 
lid and sides of the boxes in which they were placed, with such force as to be 
heard all over the house. On the 23d of May, my friend Samuel Williams, of 
the Evening Bulletin, was enjoying a picnic in the cafon mentioned above, 
when the attention of his party was drawn to a very singular noise in the 
bushes over their heads, the cause of which it was for a time difficult to dis- 
cover. At last it was found to proceed from myriads of chrysalides, attached 
to the leafless stems of the ceanothus, which, by a constant motion of their 
bodies, gave a trembling to the branches of the shrub, and produced the sin- 
gular and half weird noise referred to. The perfect insects began to appear 
on the 25th of May, and did not all emerge until the 6th of June, the average 
