238 AMERICAN HYMENOPTERA. 



pose that possibly they are, to some extent, cases of protec- 

 tive imitation. Flies are probably captured by birds in large 

 numbers, but, while bees are occasionally destroyed by the 

 same enemies, they are probably attacked much less freely 

 by them on account of their ability to sting. For this reason, 

 it would be an advantage to any species of fly, if it resembled 

 a bee closely in superficial appearance, as, on account of the 

 resemblance, it would also be less attacked by the birds. 

 Natural selection has doubtless brought about a close re- 

 semblance in many cases partly because of this advantage. 



The best examples of fly resemblance of Bombidae are 

 presented by various species of the family Asilidse. These 

 examples are numerous and only the few following ones 

 need be specifically mentioned here : 



1. Mallophora ruficauda resembles Bombus emilicB strikingly. These 

 species are both present in southern Brazil. 



2. Mallophora tibialis and Eucriiosia rubriventris both resemble 

 Bombus carolinus considerably and they probably range in habitat, 

 to a considerable extent, in common with that species in the northern 

 part of South America. 



3. Dasyllis thoracica Fabricius, D. af finis Macquart, D. tergissa 

 (var.) and D. flavicollis Say all resemble, more or less strongly, 

 Bombus impatie^is and Psithyrus laboriosus . All these Asilid species 

 have their habitats within the ranges of the bee species which they 

 resemble. 



4. Mallophora orcina Wiedemann resembles the females of Bombus 

 pennsylvajiicus ver>' strikingly. These two species range together in 

 the southeastern United States. 



5. Dasyllis sacrator Walker resembles Bombus vagans and B. per- 

 plexus very much in coloration and it ranges with these species in the 

 northeastern United States and in southeastern Canada. 



6. Dasyllis astur O. S. resembles Bombus californicus and B. vos- 

 nesenskii considerably and it ranges with those species in the Pacific 

 Coast States. 



7. Dasyllis posticata Say resembles Bofnbus fervidus females con- 

 siderably and it has much the same widely extended habitat as has 

 that species. 



Bumble-bees are captured and devoured by Asilids in con- 

 siderable numbers. The writer has many times found a 

 partly eaten bumble-bee in the grasp of one of these flies ; 

 and, in every case, the fly and bee were of very similar colora- 



