12 The Form of Insects 



hoppers, Sawflies (fig. II C, D), and Beetles for 

 example. In those beetles which live by prey the 

 teeth of the mandibles are prominent and sharp, over- 

 lapping when the jaws are closed. Some male insects 

 have the mandibles much more strongly developed than 

 have the females. This is the case in the Stag-beetles, 

 in many exotic Longhorn-beetles, and in the gigantic 

 American Lacewing-flies (Coryda/is). The mandibles 

 of Wasps are very like those of cockroaches or beetles, 

 but in Bees these jaws are small and club-shaped, being 

 used for kneading wax as well as for biting (fig. 15 m). 



Many insects have the mandibles developed not as 

 biting jaws, but as lancets for piercing animal or 

 vegetable substances from which food can be sucked. 

 Such are the mandibles of Bugs, Cicads (fig. 14 ii 

 a, b, c) and Plantlice, as well as of some two-winged 

 flies — Gadflies and Gnats for example. Mandibles 

 when modified as piercers do not move transversely 

 across the mouth, but are pushed directly outwards, 

 and drawn backwards when not in use.^ It is of 

 great interest to notice that in some of the most 

 primitive of insects, the Springtails, the mandibles 

 are withdrawn into the head-capsule and are capable 

 of both transverse and vertical motion, thus affording 

 a link between biting and piercing jaws (98). 



Some insects which feed by suction without the 

 necessity of piercing, or take no food at all in the 

 adult stage, have the mandibles in a very reduced 

 (vestigial) condition, or altogether wanting. May- 

 flies, Caddis-flies, Moths (fig. 13 m), and many two- 

 winged Flies are examples of such insects. 



Maxillae (First Pair). — The mandible of an insect 

 differs from most of the other appendages in being 

 formed only of a single sclerite. In a few beetles, 



^ But these piercers are thought by some students (4, 8) to belong 

 to the first maxilla. 



