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Insects are the largest class in the phylum Arthropoda. Like all arthropods, they have an external skeleton and jointed appendages. They must moult in order to grow.

The features that distinguish insects from the other arthropod groups (such as spiders, ticks, crabs and barnacles) include:

  • 3 pairs of legs
  • one pair of antennae
  • a 3-part body: head, thorax, and abdomen
  • compound eyes




There are nearly 30 orders of insects, but most of the more common insects belong to just 11 orders (listed in the Table below, and in the categories to the right). The table lists some of the identifying features of each of these orders. If your insect is NOT in one of these, please look under 'other insects'.

Note that the table above is based on adult insects. The early stages of many insects look very different to the adult. Where possible, we have included photos of the various life stages for each species or category.

If you are surveying aquatic invertebrates, you will almost certainly encounter a variety of insects. Some as larvae, some as adults. Some as permanent aquatic residents, but many more as visitors. The Waterbug App is an excellent guide to the diversity of aquatic invertebrates (including insects). It can be downloaded free from


Page 1 of 3 species

Heteronychus arator (African black beetle)

Heteronychus arator Liz Allen, Tura Beach
Heteronychus arator

Nezara viridula (Green vegetable bug)

Nezara viridula An early instar nymph
Nezara viridula

Periplaneta australasiae (Australasian cockroach)

Periplaneta australasiae Harvey Perkins, Montague Is.
Periplaneta australasiae


Conservation Level

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