352 NATURE SKETCHES IN TEMPERATE AMERICA 



rise in the air higher and higher to a great altitude, finally 

 becoming a mere speck in the sky. Then they move off in 

 the direction of the wind to some unknown point. I have 

 seen this remarkable migratory movement exhibited only in 

 the fall. 



Again, on numerous occasions during short flights, I have 

 observed some small insects darting from the ground into the 

 air, keeping close on the heels of the varied-wing. Sometimes 

 one, or not infrequently two, of these watchful torments would 

 arise into the air at the exact moment this locust would start 

 from the ground. In their pursuit they caught up readily 

 with their selected host, recalling to mind, in miniature form, 

 the kingbird, in his chase after the crows. But we will see, 

 in the sequence, that there is quite a different motive under- 

 lying each of these performances. I did not succeed in clearing 

 up the cause of these insect manoeuvres until the latter part of 

 August. One day I visited a dry pasture, where the >varied- 

 wing was found in abundance. Here I succeeded, after many 

 attempts, in landing in my net a varied- wing along with its 

 much desired pursuer. Here in the white folds of the net, I 

 finally had him, — a rather' large-sized, grayish fly. He was 

 identified at once as a Tachina fly. This little pest pursues the 

 locust in order to lay its egg on the neck, or under the wing 

 of the locust. The egg thus placed is out of the way of the host, 

 and it later hatches out in a grub, which eats its way into the 

 fatty parts of the locust's body, thus disabling and finally 

 killing its helpless victim. I have also seen Diptera of this 

 kind following the Carolina locust through the air. These 

 flies pass so swiftly that I had to be on the keenest lookout 

 even to see them. When they catch up with the locusts, they 

 may be seen, under favorable conditions, hovering about its 

 body for the brief space of time they ar„e within view, which 

 sometimes is only for a fraction of a second. 



The eggs of the varied- wing hatch in the spring; the young 

 maturing about the middle or the latter part of July. The 

 adults live until the advent of very heavy frosts in the fall. 

 I found them frequenting open dry woodlands, stubble fields, 

 meadows, and pasture lands. About September first, I find 

 that after half-past four o'clock in the afternoon, these locusts. 



