Insects are a class of arthropods that have three pairs of legs and, most usually, two pairs of wings. In his Prodromus of the Zoology of Victoria, McCoy depicted 26 species of insects. They were generally large-bodied and often brightly-coloured species which would have attracted people's attention. Three species, the Violet-shouldered Phasma, Red-shouldered Phasma and Australian Painted Lady, were new to science.

McCoy also featured species with an adverse effect on agriculture or forestry, such as the Vine Moth, Wattle Goat Moth and Yellow Winged Locust. His Prodromus was intended to be a practical volume to enhance prospects for commerce and industry, as well as providing detailed scientific information.

In addition to the published plates there is a significant collection of insect drawings by Arthur Bartholomew. With a few exceptions these images focus on the order Lepidoptera: moths and butterflies. For almost forty years insect larva were collected along with their host plants and brought to the laboratory for illustration.

Bartholomew would faithfully illuminate each life stage of the insect, noting the date of each successive metamorphosis. When the perfect imago (adult insect) emerged, the species would be identified by William Kershaw, pinned and entered into the collection.

The level of detail attained by Bartholomew in these illustrations makes them one of the most significant, and to this point neglected, contributions to natural history illustration in colonial Australia.