EXOPTERYGOTA 4II 



Gryllidae (crickets). The latter include a form remarkably adapted 

 for a burrowing life, namely Gryllotalpa. Nearly all these insects 

 are vegetarian, and in the Acridiidae, while the species commonly 

 live a solitary existence and are harmless, under certain conditions 

 a form with a gregarious and migratory instinct develops in countless 

 numbers which invade cultivated districts causing incalculable harm. 

 A very characteristic feature of the Saltatoria is the possession of 

 stridulating organs. In one type, exhibited by the cricket Grylhis, a 

 file on one of the anterior wings is rubbed over a scraper on the other. 

 In another type, e.g. Locusta, a row of pegs on the hind limb is 

 rubbed against a thickened area of the fore wing. Where there are 

 organs for producing sound, there are also organs for perceiving it. 

 These are tympana, chitinous ear drums, which can be set in vibration 

 and then affect special auditory sense organs. The auditory organs 

 may be found on the front tibiae or on the ist abdominal segment. 

 The posterior wings of the Saltatoria possess many parallel longi- 

 tudinal veins with a network developed between these by numerous 

 cross veins. They fold in a fan-like manner, a line of folding, the 

 anal suture, separating a prominent posterior " anal " area of the wing 

 from the main part of the wing in front. Besides the fully winged 

 forms, like locusts, there are found in the several families all stages of 

 wing reduction to mere scales as in certain stick insects, or to their 

 complete absence as in Gryllohlatta. 



Order DERMAPTERA 



Insects with biting mouth parts ; ligula two-lobed ; fore wings modi- 

 fied to form short leathery tegmina; cerci unjointed, always modified 

 into forceps; metamorphosis slight. 



The common earwig, Forficula auricularia (Fig. 306) is the best 

 example of this small but definite order. It comprises a number of 

 small, usually nocturnal insects, omnivorous in diet. The female 

 deposits the eggs in the soil, remains with them until they hatch, 

 and even protects them afterwards. The hind wings have a character- 

 istic venation and fold up along transverse as well as longitudinal 

 furrows, thus contrasting with the Orthoptera. When unfolded, 

 the wing presents the appearance of a half wheel, the "spokes" 

 radiating backwards from the anterior border, which is greatly 

 strengthened. The large posterior membranous portion corresponds 

 to the anal wing area of Orthoptera, that part corresponding to the 

 anterior area of the latter order having been greatly strengthened by 

 the coalescence of a number of longitudinal veins. The forceps are 

 organs of defence and offence. In Labidura they are used for seizing 

 the small animals on which this form lives. 



