CHAP. IV. | MEANS OF DEFENCE IN INSECTS. 4 1 



are disagreeable to their enemies. Many insects, in almost all 

 Orders, possess special glands from which they are able to 

 discharge a liquid which may be offensive tothe taste, smell, sight, 

 or touch of an aggressor. The stink-glands of many bugs arc well 

 known to most residents in India, whether by the characteristic 

 odour of the common Bed-bug or by the disgusting taste in oi 

 soup caused by a " gundy " which has been attracted by the lights 

 on the dinner-table. In such cases the glands are usually situated 

 on the lower surface of the thorax and some of the larger bugs are 

 able to project a thin stream of liquid with great accuracy for a 

 considerable distance. In Beetles the stink-glands are generally 

 situated in the anal extremity of the abdomen and are particularly 

 developed in some groups such as the Carabidas, Gyrinidze, and 

 Staphylinidae. Some members of the former group, common in 

 India under stones, etc., have earned the name of "Bombardier 

 Beetles" because they discharge a stream of liquid which volati- 

 lizes instantly in the air as a brownish mist and with quite an 

 audible report; this liquid causes a momentary severe burning 

 sensation on the human skin and would doubtless disconcert an 

 enemy sufficiently for the beetle to make its escape. Many of the 

 minute insects which cause such discomfort when they fly into the 

 human eye are Staphylinid beetles, the smarting sensation being 

 due to the acrid liquid discharged by the beetle when it finds itself 

 in danger. Some Paussid and Carabid beetles discharge a liquid 

 which has a strong smell of Iodine. 



Many Ants discharge a strong solution of Formic Acid, which 

 of course derives its name from the Latin word formic, 1, an am. 

 The common Red Tree Ant (CEcophylla smaragdina), contran. to 

 popular belief, does not Sting but grips with its jaws and throws 

 out a fine jet of liquid from the tip of its abdomen. The caterpillar 

 of Cerura vinula has glands from which it can direct a fine stream 

 of Formic Acid solution, and this seems to be used chiefly to drive 

 off parasites which endeavour to oviposit in the larva. The curi- 

 ously swollen thoracic segments of the larva of Carea subtilis also 

 contain a gland which is perhaps used in a similar way. The 

 caterpillars of the Swallow-tail Butterflies possess a curious 

 Y-shaped organ, called an osmateriutn, situated on the anterior 

 margin of the prothoracic segment, in which it is ordinarily 

 concealed; when annoyed or attacked the caterpillar can evert 

 this organ which diffuses a strong, disagreeable odour, differing in 

 various species. 



In the case of Termites the soldiers are usually provided with 

 glands in the head (sometimes extending into the abdomen), from 

 which they can pour out a thin liquid which hardens rapidly in the 



