STATES OF INSECTS. 101 



impels them to place theirs, the dung which the Scara- 

 baidce select for that purpose, and the decaying vegeta- 

 bles chosen by many other insects, a degree of artificial 

 heat must exist : and the eggs, or rather egg-like pupee, 

 of the spider-fly of the swallow {Ornithomyia Hirundinis) 

 are hatched by the heat of those birds which sit upon 

 them along with their own eggs. 



Fabricius says, " Insects never sit upon their eggs a ;" 

 but certainly, as I formerly related to you b , the female 

 earwig does this, and one would be induced to suppose, 

 from the circumstance of the you' g ones following their 

 mother, as chickens do the hen, that Pentatoma grisea 

 [Cimex Linn.), formerly mentioned, may do the same c . 



With these exceptions, the eggs of all insects are 

 hatched by atmospheric heat alone, the variations in 

 which determine the more speedy or more tardy disclo- 

 sure of the included insect. The eggs of such species as 

 have several broods in the year, as the nettle butterfly 

 ( Vanessa Urticce), when laid in summer are hatched in a 

 few days ; but if not laid till the close of autumn, they 

 remain dormant through the winter, and are only hatched 

 at the return of spring. That this difference is to be at- 

 tributed to the influence of heat has been often proved 

 by experiment: the autumnal eggs if brought into a 

 warm room may be hatched as soon as those laid in the 

 height of summer. Silk-worms' eggs naturally are not 

 hatched till they have been laid six weeks, but in coun- 

 tries where they are reared, the women effect their ex- 

 clusion in a much shorter period by carrying them in 

 their bosoms : yet to retard their hatching with particu- 



a Philos. Ent. 76. b See above, Vol. I. 358—. 



c See above, Vol. I. Ibid. 



