i28 INSECTS. 



even, as in the case of the glow-worm, without elytra; and whenever there is any 

 decided difference in coloration, it is almost invariably the male which displays 

 the brightest and most conspicuous colours. The great projecting horns and pro- 

 cesses on the head or prothorax which give so grotesque an appearance to many 

 beetles, are generally wanting or only feebly developed in, the females; and 

 these and other differences are sometimes so strongly marked that it is difficult 

 to recognise in the two sexes individuals of one and the same species. 



The larvae of beetles do not in outward appearance exhibit anything approach- 

 ing the great diversity seen in the perfect insects. They seldom display conspicuous 

 markings, and are mostly of dingy white, brownish, or black colours. The external 



structure and form vary sufficiently to make it possible 

 to tell to what family of beetles, or division of a family, 

 a larva belongs ; but, so far as species are concerned, 

 our knowledge of the larvae is extremely limited, and 

 applies to a relatively very small proportion of the 

 whole number of known species of Coleoptera. In 

 the weevils, and some other beetles, the larvae are soft 

 w T hite grubs with scarcely any trace of legs, but in most 

 of the other larvae the legs are fairly well developed, 



th U S h not S com P letel y as in the P erfect insects - 

 (nat. size). The head is always horny, and furnished with jaws 



for biting and grinding solid food. Exceptionally, 



as in the carnivorous larvae of some water-beetles, the mandibles are adapted 

 for sucking up the juices of the animals on which these larvae prey. The 

 antennae are short and few-jointed, and in some cases quite inconspicuous. Eyes, 

 when present, are always in the form of ocelli, which are grouped together in 

 varying number on each side of the head. The head is followed by a series of 

 rings or segments, of which the first three scarcely different in form from the rest 

 constitute the thorax, and give attachment to the legs. A pair of prolegs is 

 sometimes present on the last segment, but in beetle-larvae the intermediate seg- 

 ments never carry those false legs, which are so often found in the caterpillars of 

 Lepidoptera and Hymenoptera. The spiracles which are mostly hidden by the 

 elytra in the perfect insects are generally quite conspicuous in the larvae, and 

 appear as a row on each side of the body. Their number varies ; and in those 

 aquatic larvae which breathe by means of tracheal gills they are altogether want- 

 ing. When about to pupate some larvae construct cocoons of earth, or, in the case 

 of wood-boring species, they may make a shell out of fine chips and dust glued 

 together with a sticky secretion. The pupae, whether enclosed in a cocoon or not, 

 are inactive, and show all their appendages lying freely against the body, with 

 each appendage wrapped round by its own special covering of integument. The 

 larval existence of beetles varies from five or six weeks in some groups to almost 

 as many years in others ; and when conditions arise to interfere with the proper 

 nourishment of the larvae, the period may be unduly prolonged. Some of the 

 wood-boring larvae seem to live an exceptionally long time. There is at the present 

 time in the Natural History Museum in London a block, of wood containing a 

 living longicorn larva, which for the past five or six years has been feeding and 



