Coleoptera are the only order of insects that have elytra. This adaptation has enabled them to expand into many habitats such as leaf litter, logs and soil, that would otherwise damage the wings of less well protected insect groups. At first glance beetles may appear to have only 2 body segments because the elytra may cover most of the thorax and abdomen. However if you capture a beetle and turn it over you will be able to see the segments that are hidden by the elytra.
Larval Characteristics: The larvae of beetles also come in a variety of shapes and sizes depending on where they live and what they eat. Larvae generally appear grub-like with a well-defined head capsule, which may be highly sclerotised. They have short antennae and usually have chewing mouthparts. The legs may be present or absent.
Beetles are often confused with cockroaches (Blattodea) or bugs (Hemiptera) but can be distinguished from the former by their forewings which are modified into elytra and meet in a straight line down the back and from the later by their chewing rather than sucking mouthparts. Life Cycle
Beetles have a complete life cycle and development may take anywhere from a few weeks to several years. Eggs are usually laid on or near the food source such as in the soil or on a host plant, depending on the species. The number of eggs laid will depend on the species and may range from one or two up to hundreds. After hatching the larvae develop through a series of growth stages known as instars (usually 3 to 5) before pupating into adults.
Feeding
Beetles are generally herbivores, scavengers or predators, although some adult beetles do not feed at all. The greatest numbers are plant feeders in one form or another, such as nectar feeders (some Buprestidae), foliage eaters (Chrysomelidae), seed-eaters (many Curculionidae) or timber (Cerambycidae) or bark borers (Scolytidae). Others may feed on rotting wood (Lucanidae), carrion (Silphidae), dung (some Scarabaeidae), fungi or leaf litter. Some species are also predators (Carabidae) of other invertebrates. The feeding habits between larvae and adults may be the same or can vary. For example some beetle species are predatory when in the larval stage and plant-feeders when adults.
Habitat
Beetles can be found in almost all available habitats throughout Australia. Most are terrestrial though many families are largely or wholly freshwater in habit and some can be found living in marginal marine environments. In terrestrial environments beetles can be found living in soil, humus and leaf litter; under the bark of living and dead trees or in decomposing wood; under stones and logs; in dung, carrion and the fruiting bodies of many types of fungi. Some species live solely in caves while others live in the nests of vertebrates or social insects such as termites or in man-made environments such as silos where grains are stored.
In aquatic environments beetles can exploit many habitats ranging from temporary pools or mountain streams to brackish waters and mud flats. Some can be found living in the sand, gravel or mud at the edges of streams and ponds and in the high-water debris on the seashore or among the rocks and coral in the intertidal zone.