Beetles belong to the insect order Coleoptera. This name comes from the Greek ‘koleos’ for sheath and ‘pteron’ for wing, and refers to their hardened front wings – called elytra. The elytra meet along the midline of the body, enclosing and protecting the abdomen, and giving beetles their characteristic appearance.
The elytra, an armoured exoskeleton and a compact body allow beetles to live where other insects with more delicate or exposed wings would be damaged – when burrowing in leaf litter or soil, for example. These features also protect beetles from attacks. The elytra help prevent water loss by covering the openings to the breathing tubes on the abdomen.
New Zealand’s longest beetle is the giraffe weevil, also known by Māori as pepeke nguturoa or tūwhaipapa (Lasiorhynchus barbicornis). Males can grow up to 9 centimetres long, in part because of their very elongated head.
The huhu beetle (Prionoplus reticularus), its relative the spiny longhorn (Blosyropus spinosus), and the sand scarab (Pericoptus truncatus) are among the largest.
The tiny feather-winged beetles and the ant-like stone beetles, with species about 0.5 millimetres long, are among New Zealand’s smallest.
Beetles come in a myriad of shapes. Ground beetles and longhorns are cylindrical, while scarab beetles are squat. Diving beetles have streamlined bodies, perfectly adapted to the water, while weevils have comical, snout-like heads. Miniscule clam beetles are almost spherical, while bark mould beetles (Diagrypnodes wakefieldi) are paper thin, to fit beneath loose bark.
Some beetles have characteristic features, like the enlarged mandibles of male Helms’s stag beetles (Geodorcus helmsi), and the shield-like head of male fungus weevils (Hoherius meinertzhageni).
Life on the wing
Despite their hardened forewings, called elytra, beetles can fly – often rather clumsily. Unlike most other insects, beetles propel themselves through the air using their membranous hind wings. These reach beyond the elytra when extended for flight, but a complex folding system – a bit like origami – means they can fit under the elytra when at rest. Flightless beetles have reduced hind wings, and in some cases the elytra are fused.
Adult beetles lay eggs, which hatch into larvae. The larvae often live within their food source. Typically they bear no resemblance to their adult form. They have a toughened head capsule and chewing mouthparts, with a body that may be active and hard with sturdy legs, or soft and legless, protected by surrounding plant tissue or soil.
Larvae pass through several stages, called instars, before becoming an inactive pupa. As a pupa, the entire body is reorganised, until it finally emerges as a beetle. Development can take from a few weeks in some species to several years, especially if food is scarce. The adult lifespan is also variable, ranging from days, to months or years for a few larger species.