Moths and their host plants

In North Queensland there are several thousand species of moths; far outnumbering just a few hundred butterfly species. Although comparatively little is known about many moth species, they all depend on plants at some stage in their lifecycle.

Moths are much more diverse in their use of plants than butterflies, with a wide range of associations. For example, some moth larvae bore holes into trees (especially Eucalyptus) and feed on the inner side of bark. Adult FruitPiercing Moths (a pest in orchards) feed on ripe fruit. Other larvae eat the leaves of host plants and some adult moth species feed on the nectar from flowers during the day. Larvae of the bagworm moth or case moth select dead twigs to construct a protective home.

The world’s largest moth, the female Hercules Moth (pictured above at the Botanic Gardens Visitor Centre), is found in North Queensland and New Guinea rainforests. The female Hercules Moth lays eggs almost exclusively on the leaves of the Bleeding Heart Tree, Homalanthus spp. The blue-coloured caterpillars are voracious feeders and over several months reach lengths of 10cm. Adult Hercules Moths have no mouth and do not eat at all, surviving on stored reserves for less than two weeks. During this short life the female releases a strong pheromone to attract males from distances up to 2km away. After mating, she lays eggs on the host plant and the cycle continues.

Corky Bark, Carallia brachiata, a large rainforest tree closely related to several mangrove species, is host plant for the beautiful Four O’clock Moth. The caterpillars are bright yellow with rows of dark eyespots and eat the leaves of Corky Bark. Unlike the Hercules Moth, Four O’Clock Moths have mouth parts designed for feeding on the nectar of many flowers including Paperbark Trees, Melaleuca. The moths are often seen late in the afternoon, hence the common name, Four O’Clock Moth.

The Zodiac Moth (or North Queensland Day Moth) is often mistaken for a butterfly. It is a large, colourful moth that is seen in gardens during the day seeking nectar from flowers of many species, both native and exotic. Large numbers are often seen resting (usually facing downwards) in shaded areas of the garden. The larvae of Zodiac Moths eat the leaves of the Day Moth Vine, Omphalea queenslandiae. Several rainforest Wattles, Acacia spp. are host trees for the Bag Shelter Moth. Several hundred caterpillars of the Bag Shelter Moth live in a large bag constructed of silky material. At night, the caterpillars emerge from the bag to feed on the leaves of the host Acacia. The caterpillars are covered with irritant hairs that cause a severe allergic reaction. Hundreds of caterpillars often move from tree to tree in a long procession, linked head to tail, giving rise to another common name for this species, the Processionary Caterpillar Moth.

Moths and their host plants are critical for a healthy environment. They pollinate many plant species. Moths and caterpillars are also a source of food for a variety of wildlife such as spiders, lizards, birds and bats. Moths are widespread and sensitive to changes in the environment and can act as indicator species like a ‘canary in a coalmine’. The Hercules Moth, for example, is regarded as a good indicator species for the health of the Wet Tropics Rainforest.

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