8 MELANDER AND BRUES. 



new species of Plwra} This little fly takes a stand near an open- 

 ing and patiently awaits an unguarded moment. Then she quickly 

 slips in to deposit an egg in the pollen so industriously stored. 

 One Plwra persisted in her attempts to enter for several hours. 

 Driven back a half inch by the doorkeeper she gradually and 

 slowly returned until she nearly touched his face. Then a sudden 

 lunge half way out of the nest on the part of the bee would drive 

 her back again. This was repeated over and over, the dogged- 

 ness of the parasite and her slow approach seeming to exasperate 

 the little watcher. By turning his head he tried to follow her 

 movements, but from their very slowness was unable to discern 

 her position. Only when his palpi were touched would he make 

 a sudden dart. PJiora depends on her agility as well as on her 

 deliberateness. On each return of the female bee, after a fifteen- 

 minute foraging trip, the parasite would jump about excitedly 

 and possibly would get a chance to oviposit on the pollen mass 

 during a dart at the bee. A moment's rest on the threshold 

 would grant the nervous little fly ample time to infect the unsus- 

 pecting bee. The behavior of the bees towards Phora is quite 

 different from the action of ants towards these guests. Unless 

 irritated by the persistence of the parasite, Halictns is passive 

 and does not notice its presence. Even the incoming females dc 

 not'see the fly at a distance of half an inch. On the other hand, 

 ants are put in a state of fright by the proximity of these flies. 

 During the attacks of the ant-decapitating phorid, Apocephalus 

 Pergandci Coq. upon the species of Camponotus t ferruginea in 

 the north, and niacttlatus var. sansabeanns in the south, the ants 

 rush in the wildest excitement with wide-spread mandibles at the 

 agile fly. Can this difference result from the bees never seeing 

 their offspring and being consequently unaware of their fate, 

 whereas the ants have a personal acquaintance with the ravages 

 of these parasites ? It might seem so, but we must remember 

 that in the case of Pachycondyla Jiarpax, at least, a phorid larva 

 is not only tolerated in the nest, but is also fed by its host. 2 In 

 this case, however, no harm is done to the species by the pres- 

 ence of the fly, whereas with Halictns it must mean the death ot 

 the brood. 



1 P. halictoriini, described in the sequel. 



2 Wheeler, W. M., Am. Nat., 1901, p. iocf]e( seq. 



