Insects. 273 



very light blue — almost milk-coloured — Ephemerae rose into the air. 

 There were several flights or clouds at intervals through the evening, 

 and they seemed to grow continually more and more dense. I am 

 conscious that description must fail to convey an idea of the prodigious 

 numbers of individual insects, of which the several ^ clouds ' were 

 composed. I may perhaps succeed in giving some notion of the di- 

 mensions of the later flights, by stating that they extended upwards 

 as far as the eye could reach, in breadth from side to side of the river 

 — not less that twenty yards ; and were from one and a half to two 

 or more minutes in passing me, as they moved slowly along in the di- 

 rection of the stream. And so dense were these flights, that vision 

 was interfered with ; you could not clearly distinguish an object on 

 the further bank of the river. 



I first noticed them between 7 and 8 o'clock. They were numer- 

 ous, but not more so than some other species which are often seen in 

 the evening. At this time they were dispersed in all directions : the 

 large clouds had not begun to appear ; and when they did, it made 

 no diminution in the number of stragglers, which, in fact, continued 

 to increase as long as I remained by the river, — until nearly 10. 



My attention was first particularly drawn to them by their settling 

 on various parts of my dress ; and about 8 o'clock there must have 

 been hundreds on my hat, coat and waistcoat. In the course of a 

 short time, on casting another glance at my spotted sleeve, I observed, 

 in addition to the insects themselves, which were quite as numerous 

 as before, a quantity of exuviae or skins adhering to the cloth. This 

 led me to watch them closely : and it was quickly apparent that their 

 object in settling was to find a resting-place during the time about to 

 be occupied in divesting themselves of an external skin or envelope. 



Soon after an insect had alighted, the tail was somewhat elevated, 

 the whisks or setae made to diverge to their full extent, and the end 

 of the body energetically moved from side to side for the space of a 

 minute or two. Simultaneously with this motion the fly continued to 

 move backwards, apparently endeavouring to fasten its feet firmly to 

 the cloth, so as to remain fixed during the approaching change. When 

 the motion of the tail ceased, the whisks lost their divergency, and the 

 insect remained motionless for a few seconds. 



Up to this time the wings had been in a horizontal position, — ex- 

 panded, as a butterfly's are sometimes seen, when it is resting on a 

 flower, or on the ground : but now they began to be first elevated a 

 little, and then depressed as much as possible. This was just the kind 

 of action a man, who wished to burst his coat on his back, would use; 



T 



