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 
aesthetic 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 
