INSECTS. 
128 
Zabrus gibbus and its larva 
(nat. size). 
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 larvse are soft 
white grubs with scarcely any trace of legs, but in most 
of the other larvse 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 larvse of some water-beetles, the mandibles are adapted 
for sucking up the juices of the animals on which these larvse prey. The 
antennse 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 Histoiy Museum in London a block of wood containing a 
living longicorn larva, which for the past five or six years has been feeding and 
