Many native moths are of economic importance as pest species, the most notable probably being the subterranean grass caterpillar moths (Oxycanus spp.) which are second only to the common grass grub beetle (Costelytra zealandica) as pasture pests. In exotic forest plantations sometimes the looper caterpillars of the genus Selidosema cause considerable damage. The noctuid moths (rather heavy, large, dusk- or night-flying species) cause considerable damage to many plants. In this group are the “army-worm” caterpillars which, under suitable conditions, devastate large areas of pasture or crops.
The largest moth in New Zealand is the wood-boring hepialid, Charagia virescens, which is green or yellow with silvery wing markings; it frequently appears at night during wet summer weather. Another rather interesting species is the common “bag moth” whose caterpillars live within a suspended tough bag often covered with a camouflage of pieces of twigs, bark, and leaves. The females of this moth are wingless and often do not leave the larval case. This species is known to science as Oeceticus omnivorus and is sometimes responsible for considerable damage to trees, damage which would undoubtedly be of considerably greater importance were it not for the presence of several parasites which normally keep the moth populations to a low level.