124 TRUE TALES OF THE INSECTS. 



without descending. That as a rule swarms under favour- 

 able conditions arise in the morning, about eight to ten 

 o'clock, after the dew is off, and the warmth of the sun 

 is felt, and settle down again to eat as night approaches, 

 by four or five in the afternoon, is well established ; 

 that is, they can sustain themselves an entire day in the 

 air. The rate at which they travel is variously estimated 

 at from three to fifteen or twenty miles per hour, deter- 

 mined by the velocity of the wind ; a day's flight may 

 therefore be estimated at from twenty to a hundred 

 and fifty miles. But there are numerous facts which 

 go to prove that a single flight may extend much farther 

 than the longer distance here given : many persons 

 believe the insects can remain in the air for days with- 

 out coming down. While this is an extreme opinion, 

 it seems undoubtedly true that they do sometimes 

 continue their flights for more than a day; that 

 they may, and do travel at night, has been recently 

 clearly shown. Their general habit of alighting in the 

 evening and resuming their journey next day after sun- 

 rise, if the weather is fine, together with the difficulty 

 of observing them at night, have led to the general, 

 but erroneous, impression that there are no exceptions 

 to the rule. 



There are good reasons for believing that the 

 exceptions are much more numerous than might be 

 supposed, that it is no uncommon thing for the insects 



