EARWIG 



179 



life the three thoracic pairs of spiracles are alone easy to detect. 

 The first dorsal plate of the abdomen is united, but not perfectly, 

 with the thorax, a feature of interest when we recall the com- 

 plete union that exists in the same region of the wasp and other 

 Hymenoptera, and that has given rise to the propodeum (vide 

 p. 197). In the living animal the abdominal segments overlap 

 each other like tiles, and thereby gain strength to resist external 

 pressure ; nevertheless the soft intervening portions render 

 possible great distension and flexibility. The forceps differ in 

 shape in the two sexes. In the female their " jaws " are almost 

 straight, with roughened inner edges and crossing tips. In the 

 male the " jaws " are curved into a semicircle, strongly toothed 

 at their contiguous bases, but smooth on the curved part. The 

 size, shape and proportions of the male forceps are extremely 

 variable, as is so often the case with highly specialised organs ; 

 cf. the mandibles of the male stag-beetle. Reference has already 

 been made to the use of the forceps in tucking away the flight- 

 wings beneath the tegmina, but that this is not their sole use 

 is evident from the fact that wingless species of earwigs likewise 

 possess these organs ; nor is the nip that they can give when 

 employed in defence sufficiently formidable to be of much value. 

 It is possible that they are in some way concerned with the process 

 of mating, but we find no recorded observations on this point. 



The means of defence possessed by earwigs are of the passive 

 order. Thanks to its skulking habits during the day, it escapes 

 from many insectivorous creatures. But it also has a most 

 disagreeable odour, which is very noticeable if a number of speci- 

 mens are kept together in a small box or on any article in which 

 these animals have congregated for shelter. This odour is pro- 

 duced by special glands situated on each side of the dorsal surface 

 of the (apparent) second and third abdominal segments ; the 

 position of these glands is visible to the naked eye, being indicated 

 by a slightly raised line which ends in a slight fold at the hinder 

 edge of the dorsal plate of the segment. There is also on the 

 dorsal surface of the segments a series of dark, smooth, short 

 marks, two on each side of each segment, whose significance is 

 unknown. 



During the winter the insects bury themselves in the soil or 



