AMERICAN PILOSE FLIES AND BUMBLEBEES. 273 



inal segments, which are covered with black hairs. The same 

 distribution of yellow and black hairs on the thorax and abdomen 

 is characteristic for all the eastern species of pilose flies. Mallota 

 posticata (PI. I., 18, 19), Mallota cimbiciformis (PI. I., 20-22), 

 Eristalis flavipes (PI. I., 23-24), Eristalis bastardii (PI. I., 26-27), 

 Dasyllis lata (PI. II., 9), Dasyllis marquarti (PL II., 9), Das. 

 sacraton (PI. II., 9), Das. champlaini (PL II., 8). All these 

 Syrphidx and Asilidx are very common in the eastern states and 

 can be found on the same flowers with Bombus. 



Six bumblebee species of the eastern states, namely Bombus 

 vagans (PL III., i), B.affinis (PL III., 7), B.impatiens (PL III., 3), 

 B. separatus (PL III., 2), B. bimaculatus (PL III., 5), B. perplexus 

 (PL IV., 4) have a coloration exactly corresponding to Volucella 

 evecta americana (PL I., 15) and to the other Syrphidx and 

 Asilidx which are mentioned above. (Compare PL I., 15, with 

 PL III., i, 7, 3, 2, 5, 4. Compare also PL II., 7, 8, 9, with PL III., 

 ! 7 3) 2 > 5. 4 an d then PL II., 10, n, with PL III., 13, 14, 15.) 



Four other eastern bumblebee species, namely B .pennsylvanicus 

 (PL IV., 13, i/[),B.auricomus (PL IV., 13, 14), B. terricola (PL IV., 

 14) have a slightly different distribution of black and yellow hairs 

 on the thorax and abdomen. This group of bees has its corre- 

 sponding group of flies. It is hardly possible to detect any 

 difference between the eastern Eristalis flavipes (PL I., 24) var. 

 b., Dasyllis dithoracica (PL II., 10, n), Das. grossa (PL II., n) 

 and the bumblebees enumerated above. The flies are generally 

 like the females, workers and males of the corresponding bumble- 

 bee species, but this is only true when the Hymenoptera has no 

 polymorphic females or males. B. bimaculatus (PL III., 5) of 

 this first eastern group, which is like V. evecta americana, has a 

 male variety colored like Eristalis flavipes var. b (PL I., 24), 

 Eristalis flavipes, on the other hand, has just been compared 

 with the bumblebees of the second eastern group. (The groups 

 are divided here only in relation to their color patterns.) We find 

 the same phenomenon in B. affinis (PL III., 7), and B. pennsyl- 

 vanicus, both of which have three types of males; (PL IV., 10, 1 1. 

 15-18) one of these is like the female, but the two others are 

 entirely different. The latter two are extremely like Criorhina 

 verbosa (PL II., 14) and Criorhina Kinkaidi var. b (PL II., 16). 



