3092 



THE JOINTED ANIMALS 



structure of the tarsi, differences in the two sexes are frequently to be noticed. 

 When the male is fully equipped for flying, the female may be without wings, or 

 even, as in the case of the glowworm, without elytra; and whenever there is any 

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

 brightest and most conspicuous colors. The great projecting horns and processes 

 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 recognize 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 conspicu- 

 ous markings, and are mostly of dingy white, brownish, or black colors. 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 propor- 

 tion of the whole number of known species of Coleop- 

 tera. In the weevils, and some other beetles, the 

 larvae are soft white grubs with scarcely any trace of 

 legs, but in most of the other larvae the legs are 

 fairly well developed, though not so completely as in 

 the perfect insects. 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 man- 

 dibles 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 inconspic- 

 uous. Byes, 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 interme- 

 diate segments never carry those false legs, which are so often found in the cater- 

 pillars of l,epidoptera 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 larva which breathe by means of tracheal gills they are altogether 

 wanting. When about to pupate some larvse 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 inclosed 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 



Zabrus gibbus and its larva. 

 (Natural size.) 



