272 ENTOMOLOGICAL NEWS [Nov., '22 



Studies in the Genus Hetaerius (Col., Histeridae). 



By J. O. MARTIN, Berkeley, California. 



All of the members of this interesting genus of the Histeridae 

 are. so far as at present known, myrmecophilous and aside 

 from this, little exact knowledge exists as to their life histories 

 or their relations to their hosts. Although they live at the 

 ants' expense, they show no signs of the degeneracy so often 

 accompanying parasitism and seem to be as efficient as any of 

 the family to which they belong. They have well developed 

 wings and can use them and their legs, while apparently awk- 

 ward, get them over the ground at a surprising rate. The 

 compact body of these beetles is strongly chitinized and with 

 its retractile head and antennae, its broad flat legs, serving as 

 additional abdominal protection, offers impregnable defense to 

 attacks of the ants. It is quite evident, from numerous obser- 

 vations, that the ants tolerate these beetles owing to secretions 

 which they exude and of which the ants are very fond. These 

 secretions are believed to arise at the basal thoracic angles and 

 there are specializations at these points which seem to support 

 this idea. Also the ants are known to favor this region, even to 

 the extent of gnawing holes through the thoracic walls, presum- 

 ably while the chitin is soft directly after emergence from the 

 pupa. 



The members of this genus are all of small size, varying in 

 length from one and a half to three millimeters. The general 

 form of the body is quadrately oval with variations in the ratio 

 of length to breadth as well as to convexity. The general body 

 color does not vary greatly in the different species, being a 

 reddish brown similar to that common to many other insects 

 of myrmecophilous habits. In vestiture there is a variation 

 from almost complete nudity, to a considerable degree of hair- 

 iness. The hairs themselves vary from plain bristles, through 

 different degrees of plumosity to a squamose type which is 

 generally plumose and recumbent. These hairs offer useful 

 taxonomic characters, but should be used with caution as I am 

 convinced that the ants frequently gnaw some of them off. 



The form of the prothorax is a very useful means of specific 

 determination and as there is a very unusual development of 



