Mosquitoes and Parasite Problems. 149 



it or knock it off, would be a case parallel to that 

 of the bird-fly on the small bird. It might be 

 supposed that the Firewood-gatherer, like some 

 ants that keep domestic pets, makes a pet of the 

 fly; for it is a very pretty insect, barred with 

 green, and with rainbow reflections on its wings 

 and birds are believed by some theorists to possess 

 gesthetic tastes ; but the discomfort of' having such 

 a vampire on the body would, I imagine, be too 

 great to allow a kindly instinct of that nature to 

 grow up. Moreover, I have on several occasions 

 seen the bird making frantic efforts to capture one 

 of the flies, which had incautiously flown up from 

 the nest at the wrong moment. Bird and fly seem 

 to know each other wonderfully well. 



Here, then, we have a parasitical insect specialized 

 in the highest degree, yet retaining all its pristine 

 faculties unimpaired, its love of liberty, and of asso- 

 ciating in numbers together for sportive exercises, 

 and well able to take care of itself during its free in- 

 tervals. And probably when thrown on the world, as 

 when nests are blown down, or the birds get killed, or 

 change their quarters, as they often do, it is able to 

 exist for some time without avian blood. Let us then 

 imagine some of these orphaned colonies, unable to 

 find birds, but through a slight change in habits or 

 organization able to exist in the imago state with- 

 out sucking blood until they laid their eggs ; and 

 succeeding generations, still better able to stand 

 the altered conditions of life until they become 

 practically independent (like gnats), multiplying 

 greatly, and disporting themselves in clouds over 

 birdless forests, yet still retaining the old hunger 



