OF WASHINGTON. 5 



BRANCHED HAIRS OF HYMENOPTERA. 

 By A. N. CAUDELL. 



Several years ago, in an attempt to determine which of our 

 Hymenoptera possess branched hairs, I examined almost two 

 hundred species, including representatives of all the families. Of 

 these species twenty-three only possessed branched hairs, the 

 others having only simple ones, which, in some cases, were 

 spirally twisted. Without exception the twenty-three species 

 bearing branched hairs proved to belong to the group Antho- 

 phila, or pollen-gatherers, and no representative of this group 

 was found without such hairs. Thus the possession of branched 

 hairs seems a good character for the separation of the Antho- 

 phila from the remainder of the Hymenoptera. This character 

 has indeed been used by some writers. 



Of the Anthophila somewhat critical studies of the hairs from 

 various portions of the body were made for the purpose of learn 

 ing the distribution of the various forms, and at which portion 

 of the body they were the most often found. Characters among 

 the hairs for the subdivision of the group were also sought for. 



It has generally been stated that branched hairs are found 

 especially on those portions of the insect's body that are used in 

 gathering pollen. In my investigations I examined hairs from 

 the head, dorsal surface of the thorax, dorsal and ventral sur 

 faces of the abdomen, posterior tibiae and basal segment of the 

 posterior tarsus. I found that of these six regions the dorsal 

 surface of the thorax alone possesses branched hairs as a constant 

 character. The thorax must, therefore, be considered the typical 

 branched-hair bearing region, as it is the only place where such 

 hairs are found to be always present. If exceptions should be 

 found to occur here also upon further investigation, is not known. 



The invariable presence of branched hairs on the top of the 

 thorax seems a wise providence of nature for facilitating the 

 cross fertilization of plants. 



In regard to finding hair characters for the subdivision of the 

 Anthophila I met with no success. While the forms of hairs 

 vary from one- to many-barbed and from short serrations to 

 long branches, the various kinds are distributed among the 

 genera in such a manner as to be, apparently, of no systematic 

 importance. The hairs of closely related genera, as Bombus 

 and Psithyrus, present no characters for their separation or for 

 the separation of such genera from ones remotely related. Nor 

 do the hairs of the Andrenidae seem to differ from those of the 

 ApidaB any more than they do as between different genera. 



This subject seems to have received less study than its interest 



