MEANS OF DEFENCE OF INSECTS. 267 



sentinels, avoiding- with the utmost caution, as if she 

 were sensible that her safety depended upon it, all con- 

 tact with their antennae. These bees upon guard in 

 the night, are frequently heard to utter a very short 

 low hnm: but no sooner does any strange insect or 

 enemy touch their antennas, than the guaid is put into 

 a commotion, and the hum becomes louder, resembling 

 that of bees when they fly, and the enemy is assailed by 

 workers from the interior of the hive''. 



To defend themselves from the death's-head hawk- 

 moth, they have recourse to a difterent proceeding. In 

 seasons in which they are annoyed by this animal, they 

 often barricade the entrance of their hive by a thick 

 wall made of wax and propolis. This wall is built 

 immediately behind and sometimes in the gateway, 

 which it entirely stops up ; but it is itself pierced with 

 an opening or two sufficient for the passage of one or 

 two workers. These fortifications are occasionally va- 

 ried : sometimes there is only one wall, as just de- 

 scribed, the apertures of which are in arcades, and 

 placed in the upper part of the masonry. At others 

 many little bastions, one behind the other, are erected. 

 Gateways masked by the anterior walls, and not cor- 

 responding with those in them, are made in the second 

 line of building. These casemated gates are not con- 

 structed by the bees without the most urgent necessity. 

 When their danger is present and pressing, and they are 

 as it were compelled to seek some preservative, they 

 have recourse to this mode of defence'', which places 

 the instinct of these animals in a wonderful light, and 

 shows how well they know how to adapt their proceed- 



» Huber, Nouv. Obs. ii. 113. " Ibid. 294— 



