274 OBSERVATIONS ON INSECTS. 



be dead and stiff, and what is more, in some cases 

 firmly glued down to the surface of the leaf by a 

 sort of cottony mildew. This seems owing to the 

 chill and dampness of an autumnal night coming 

 suddenly on, and surprizing such individuals as had 

 been tempted out of their hybernacula by the morn- 

 ing's sun ; rendering them powerless, and unable to 

 effect their retreat in time. The same circumstances 

 promote the growth of the mildew, by which their 

 death is accelerated, if it be not mainly owing, in 

 the first instance, to the attacks of that fungus. 

 I observe this frequently about the latter end of 

 October or beginning of November, when the tem- 

 perature of the air at sunset, especially if the sky be 

 clear, falls very rapidly, and radiation also exerts a 

 powerful influence in cooling down objects that are 

 much exposed. Sometimes flies may be observed on 

 windows, killed in the same way, and presenting a 

 similar appearance. In both cases, many of the in- 

 dividuals so nearly resemble living insects as almost 

 to deceive an entomologist ; and I have occasionally 

 approached with unnecessary caution to entrap with 

 the forceps what I conceived to be a fly basking on 

 a leaf. * 



* The above is extracted from a journal- book of mine bearing 

 the date of 1824. Since then the observation recorded has been 

 often made by others, and many suggestions offered in explana- 

 tion of the fact. See London's Magazine of Natural History, 

 (vol. vii. p. 530,) where there are several similar remarks by dif- 

 ferent observers. The cottony mildew above spoken of appears to 

 be a peculiar fungus found on flies only. Mr. Berkeley (in a letter 

 dated Dec. 5, 3837) informed me that he believed it to be the 



