394 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 12 



time during the winter are the ladybirds entirely dormant. The warm 

 rays of the sun on mild days cause more or less activity among them, 

 either in the form of an oscillating movement within the shelters or 

 a migration along the trunk to other cavities. 



Other forms of heat cause activity. An instance of this nature 

 occurred in which a horse left tied close to a tree harboring this lady- 

 bird had his abdomen almost completely covered with the beetles in 

 i a short time. The heat of the animal had evidently awakened them 

 to activity and, using the rein as a bridge, they had crawled beneath 

 the horse's blanket, much to the animal's chagrin, and he was unable 

 to get rid of them by switching his tail. 



Early in spring the beetles leave the trees and scatter in the sur- 

 rounding fields. 



To account for their repeated return to the same trees for successive 

 years several theories were considered. One theory was that as lady- 

 birds are known to emit a strong odor, the trees become impregnated 

 to such a degree as to serve as an attraction to future generations. 

 Although no such odor could be detected at any time it was thought 

 possible that our limited olfactory senses failed to detect what was 

 perhaps quite keen to the insects. Nevertheless the cavities remain 

 unoccupied for at least eight months of the year, during which time 

 the tree is constantly exposed to the elements; besides, the odor must 

 be penetrating to attract the insects from a considerable distance. 



Afterwards, the natural odor from the tree was considered as a pos- 

 sible attraction, yet the variety of trees which they frequent together 

 with the fact that they also hibernate between boards along fences 

 and among piled stakes, precludes the serious consideration of this 

 theory. Experiments were made by confining slabs of bark of oak, 

 maple, cedar and mulberry in cheesecloth cages and liberating lady- 

 birds in them to determine whether or not the odor of the bark would 

 attract them. In every instance the beetles entirely ignored the bark, 

 preferring to hide in the crevices made by the cloth and supporting 

 posts. 



The possibility of an inherited instinct of attraction to trees was 

 also considered as a plausible factor. The fact that the beetles return 

 to the same trees year after year, however, and the further fact that 

 some individuals hibernate on material other than trees, necessitates 

 the abandonment of this theory also. 



Finally, the conclusion was reached that frequent hibernation on 

 the same trees is purely accidental, or merely a matter of convenience, 

 being confined to those beetles in the immediate vicinity and to acci- 

 dental individuals from among those hibernating on other material. 



The process by which the species manages to assemble on the same 



