Key to Australian Freshwater and Terrestrial Invertebrates

Phylum Arthropoda
Subphylum Hexapoda
Class Insecta
Order Lepidoptera

Common names: butterflies and moths

Overview

Lepidoptera, or butterflies and moths, are one of the best known and easily recognisable orders of insects. Adults have two pairs of membranous wings, covered, usually completely, by minute scales that are often patterned and can range from dull greys and browns to beautiful iridescent bright greens, blues and reds. In a very few species, the wings are reduced or absent (often in the female but not the male). Antennae are long and slender in female moths, in males generally feathery and used for detecting female pheromones. Butterflies have clubbed antennae. Lepidopterans have large compound eyes and their mouthparts are adapted into a long feeding tube (proboscis) for sucking nectar; the proboscis coils under the head at rest. A few species have reduced mouthparts, or no mouthparts at all (some species do not feed as adults), while in others they are modified to pierce and suck blood or liquids in fruit. Lepidoptera vary greatly in size, wingspans range from 3�250 mm. Lepidopteran larvae, commonly known as caterpillars, have a toughened (sclerotised) head capsule, chewing mouthparts, and a soft body that may bear hairs or spines. They have three pairs of true legs (thoracic legs) and, on the abdomen, up to five pairs of prolegs. Prolegs are leg-like processes, bearing a ring of tiny hooks (crotchets), that assist with walking.

Distribution and diversity

Lepidoptera are found in most terrestrial habitats across the globe where the range of their food plants largely determines their distribution. They are particularly diverse in the tropics and are one of the four mega-diverse orders of insects, along with the Coleoptera, Diptera and Hymenoptera. More than 180,000 species are described worldwide and, while 10,600 are known from Australia, this is likely to represent only about half the true number of species.

Life cycle

Sperm transfer in moths and butterflies is direct and oviposition is probably stimulated by odours given off by the host plant. Eggs are usually laid on or near the caterpillar's host plant, either separately or in groups, although some scatter their eggs in flight or in loose masses on the ground. A female may lay only a few eggs or tens of thousands depending on the species; several hundred is typical. After hatching caterpillars usually develop through 4�7 larval instars over a period of a few weeks to a few months, depending on the species, before pupating. When ready to pupate caterpillars generally find a sheltered site to spin a cocoon or simply to pupate. Some may pupate attached to vegetation, others in soil or leaf litter or inside the wood they have been tunnelling. Many moths and butterflies have one or two generations each year; some breed continuously. Species belonging to the large wood-boring family Cossidae may take up to five years to develop.

Feeding

Adult lepidopterans are generally nectar feeders using their long proboscis to suck up fluid, although a few have reduced or absent mouthparts and do not feed at all. Most larvae are herbivores typically feeding on foliage or wood, usually with a rather narrow range of host plants. Other species are detritivores feeding in leaf litter, and a few are carnivorous, cannibalising other caterpillars or feeding on soft-bodied insects such as scale insects (Hemiptera) or ant larvae.

Ecology

Larval caterpillars can be found on all plant parts including flowers, seeds, leaves, fruit, bark, wood and roots. Many are camouflaged, matching their food plants, and may adopt postures, such as looking like a twig, that enhance their protection from predators. In addition, as deterrents to predators, many have bright warning (aposematic) colourations, typically associated with unpalatability, such as a bitter taste, or mimicry of those species that are unpalatable. Others have hairs and spines that can produce a stinging sensation. Many species can drop away from danger on a thread of silk when threatened. Adult butterflies are generally be seen flying close to their food plants during the day. Moths are mostly nocturnal and may be attracted to light at night or observed during the day resting, camouflaged, on tree trunks and other surfaces, in dark crevices or on their host plants. Adults may be solitary or form large groups for mating, migration or roosting. Like the larvae many also display aposematic colourations to deter predators. Being predominantly plant-feeding, the larvae are important herbivores in a wide variety of habitats. In addition, many species cause significant economic losses to agricultural crops due to feeding damage. Many of these pest species in Australia are native and have moved onto crops, for example the light brown apple moth, Epiphyas postvittana, whose larvae feed on a wide range of native plants, is now a pest on many crops both in Australia and overseas. A few species have been introduced as biological control agents of weeds, for example, the iconic South American Cactoblastis cactorum that effectively controlled prickly pear, Opuntia spp. in NSW and Qld.