36 VESPERTILTONID^. 



wholly retire into a state of undisturbed hibernation 

 until the winter has decidedly set in : its torpidity, there- 

 fore, can hardly be said to continue more than from two 

 to three months. A specimen was shot by Mr. Gould, 

 in the middle of a bright, sunny, but frosty day, just 

 before Christmas. Their final retirement does not de- 

 pend exclusively upon temperature ; for although before 

 the severe frosts set in they continue to fly even when 

 it is below the freezing point, they do not again appear 

 until the time above mentioned, notwithstanding the 

 thermometer, as Mr. Jenyns has observed, may have 

 often risen considerably above 50 of Fahrenheit. This 

 peculiarity is of easy solution. The fondness of the 

 animal for different species of gnats has been observed 

 even from the earliest period ; * and from the diminu- 

 tive size of the Pipistrelle, it is probable that these 

 little insects constitute its principal food. These and 

 many other dipterous insects, after having disappeared 

 during the ungenial fogs and rains of the close of au- 

 tumn, often make their appearance again in smaller num- 

 bers, on every fine warm day, until the severe cold of the 

 depth of winter finally destroys the greater part of them. 

 The same impulse of hunger equally accounts for the 

 appearance of the Pipistrelle in the daytime at this 

 period of the year ; and it is only at that time that the 

 temperature is sufficiently elevated to summon into 

 temporary activity its insect food. 



Mr. Jenyns remarks, that each species of Bat ap- 

 pears to have its own peculiar place of concealment ; 

 and that while the Noctule resorts to hollow trees, and 

 the Long-eared Bat to roofs of houses, the present 

 species is found in " crevices of decayed brick walls, 

 in the cracks of old door-frames, or behind the leaden 



* u Et in cibatu culices gratissimi. " Plin. 



