3S8 



ANIMAL DEFENCES 



tip of the abdomen is provided in bees, wasps, and ants. This 

 weapon may be used in some cases more tor offence than defence, 

 as in those digging wasps (see p. io6) which lay up a store of 

 spiders or insects for the benefit of their larvae, but in ordinary 

 bees its chief use would appear to be that of defence. The hard 

 parts of a Bee's sting (fig. 505) consist of three rods, of which one 



acts as a "director", along which the 

 other two can be moved backwards 

 and forwards, each of them presenting 

 a longitudinal groove which works 

 along a corresponding ridge. Each of 

 these two " piercers " is a kind of 

 flattened stylet, the tip of which is 

 studded with a number of barbs. 

 There are two poison-glands secret- 

 ing respectively an acid and an alka- 

 line secretion, and opening into a blad- 

 der-like sac. This in its turn pours 

 its fluid into a sort of reservoir formed 

 within a swelling at the base of the 

 director, and thence it is conducted to 

 the wound along a channel between 

 the director and the two piercers, each 

 of the latter possessing a projection 

 which acts as a piston. It is well 

 known that when a bee uses its sting, 

 the piercers, being barbed at their tips, cannot be withdrawn, and 

 are left sticking in the wound, while the attempt to withdraw them 

 commonly proves fatal to their possessor. The sacrifice of the 

 individual, however, benefits the species, for insectivorous animals 

 commonly avoid bees (see p. 307). Female Wasps and Ants 

 possess weapons of similar character, but the piercing stylets are 

 not barbed, and can therefore easily be withdrawn, so that the 

 individual is not liable to perish for the benefit of its kind. 



Insects not uncommonly possess variously-situated glands that 

 secrete an offensive, or it may be acid, fluid, by the sudden ejec- 

 tion of which enemies may be discomfited. A well-known instance 

 is that of the Bombardier-Beetle iyBrachinus crepitans), which is 

 provided with glands connected with the last part of the intestine 

 {rectitni). These secrete a volatile fluid which can be suddenly 



Fig. 505. — Sting of Bee 



On the left one of the piercers is shown in 

 side view, much enlarged. On the right a cross 

 section through the sting, very highly magni- 

 fied : aa, the director, on the upper side of 

 which are two ridges, bb, along which the two 

 piercers slide. 



