THEIR RELATION TO EACH OTHER 103 



we find a very decided specialization as to the char- 

 acter of the prey. Almost all the members of the family 

 are predatory during the larval stage, but they are not 

 general feeders; some of them are even very closely 

 limited as to food, and form specific checks of the very 

 highest importance. Remove one of these checks and 

 the host may become immeasurably destructive: re- 

 store it and, no matter how much the host has gained, 

 the check will regain control. Plant lice and scale 

 insects are the especial prey of these beetles and the 

 facts just recited are within the observation of almost 

 every student of entomology. We are in the habit of 

 thinking of "ladybird beetles" as being red or yellow 

 in color with black spots, and as nearly hemispherical 

 or at least convexly oval in form. The form is quite 

 constant indeed, but the colors are by no means all 

 gay. Besides the red, yellow and black species there 

 are those that reach to metallic blue and yet others 

 that are dull or shining black with very little if any 

 maculation. The variation in size is also considerable, 

 for while we have giants half an inch in length, we 

 have pIso midgets not much more than one one-hun- 

 dredth of an inch over all. 



Is there any unusual increase of a plant louse or 

 scale species: in a few weeks their ladybird enemies 

 will be found to be on the increase as well, and very 

 often, even before the end of the season, the control 

 will be re-established; for many of these species have 

 several broods during the year and plenty of food is 

 conducive to quick development. Even a normally 

 rare species may under such a spur become abundant. 

 An example of such control I have seen on several 

 occasions in the case of a plant louse that infests Nor- 

 way maples, by the 15-spotted ladybird, which is not 

 usually common. When weather conditions during 



