Insect external structure
Insect internal structure
Development of insects
Relationships of insects
Insect identification > Coleoptera
There is a great diversity in the structure of the antennae in different beetles, and also in the form of the legs and number of tarsal segments. The arrangement of the skeletal plates around the articulation of the fore coxae to the body is also variable and of importance in classification. Eggs of the Coleoptera are laid in many kinds of places-on leaves, in branches, in decaying matter, water, etc.
The larvae which hatch are usually called "grubs" except when they bore in wood. Then, as with larvae of any order found under such conditions, they are termed "borers." They usually have the three pairs of legs which become those of the adult, though these are sometimes wanting.
Some feed upon other animals, some on leaves or wood, some on carrion and others on various substances. After full larval growth has been attained, they pupate. The pupal shell or skeleton generally covers the surface of the body closely, but the wings and legs though lying close to it are covered separately as projecting appendages and not sheathed by the shell enclosing the body proper. Such a pupa is called a pupa libera, or free pupa . In some Coleoptera this condition does not obtain, the pupa shell enclosing wings, limbs and body with no projecting appendage sheaths, and such a case is called a pupa obtecta.
The beetles are generally divided as a matter of convenience into the true Coleoptera (Coleoptera genuina or Coleoptera vera) and the snout beetles (Rhynchophora), though it is at least doubtful if the latter is a natural group.
The insects in this section are easily recognized, in most cases, by having the front of the head prolonged into a snout which may be long and slender-in some cases even longer than the body-or short and stout, being sometimes so short as to be hardly noticeable. The antennae arise from the sides of the snout and in most cases have a bend like an elbow near the middle. The mouth-parts are at the end of the snout but may be differently modified in different species. The insects of this group are even more firm bodied than most other Coleoptera. The true beetles (Coleoptera vera) have no snout. The mouth-parts are all present and as a group its members average larger than the Rhynchophora-indeed the largest bodied insects known belong here.