GUESTS AND PARASITES OF HALICTUS. 7 



stubborn gate-keeper. Finally she turned about and crept back- 

 ward to the male, resting a moment with her sting before his 

 face. When she now turned, the male seemed convinced, and 

 the wearied female entered in the usual way. In this case did 

 the female flaunt her own poison to overcome that of Mutilla as 

 a passport to her home ? It might seem so ; but the simplicity 

 of such a physiological action is quite equalled by the complex- 

 ity of the intelligence displayed. 



When a male bee guards the opening the approach of Mutilla 

 produces a far different effect upon the watcher. Instead of 

 rushing out on the marauder, the defenseless male adopts the less 

 foolhardy measure of "turning tail," but still keeps at the en- 

 trance of the nest. Now the convex abdomen neatly fits the 

 opening, forming a parasitic-proof shield, and Mutilla must needs 

 leave. When no other bee is behind a female watcher, she never 

 rushes out, leaving the nest unguarded, but adopts a manceuvre 

 similar to the male's, but instead of inflexibly curving her abdo- 

 men over the opening, she reaches afar with her sting. 



Canadensis, however, is not the only Mutillid that worries the 

 Halictines. On numerous occasions Myruwsa iinicolor Say^ and 

 Mutilla infcnsa sp. nov. were found crawling about, but these species 

 do not appear to have become nearly so annoying. From one 

 square meter of Halictus-co\ox\y fully fifty specimens of canadensis 

 were taken during the summer, whereas in all but ten specimens 

 of the Myrmosa were observed. Mutilla fcrnigata Fabr. and 

 vesta Cresson were also found prowling over the nests, though 

 these species are doubtless parasitic on the larger burrowing in- 

 sects which associate with Halictns, for the large size of their 

 bodies would not permit entrance into the Halictus nests. More- 

 over, they may crawl quite close to the doorkeeper and elicit no 

 attention ; possibly their stridulation is pitched to an unrespon- 

 sive key and their odor stimulates no reaction. 



Almost as ardent a persecutor of the bees is to be found in a 



1 It IS time to abandon superfluous names. Myrmosa unicolor Say, described as a 

 male, and M. thoracka Blake, described as a female, have paraded in collections 

 quite long enough as distinct species. Inasmuch as Mr. H. L. Viereck has recently 

 taken the initiative {Ent. Ncws, 1902, p. 72) in consolidating some of the species of 

 Mutillidcx, we shall follow him in the nomenclature of this paper. The males of this 

 species fly abundantly among the roadside flowers, in company with males of cana- 

 iensis 2ind ferriigrJta { = casior BXskt^ Lepeleterii Fox Ifeneslrata Lepeletier] ). 



