There are around 30 different orders of insects in the world. Beetles, wasps and their relatives, butterflies and moths, flies and their relatives and true bugs are the five largest. Other orders include dragonflies, cockroaches, termites, Orthoptera (grasshoppers and crickets), caddisflies, stoneflies, mayflies, thrips, lice and fleas.

      Let’s start with beetles (Coleoptera) – one of the largest orders of insects worldwide, despite tough competition from the wasp order, where improved knowledge is leading to a steady rise in the number of species. The hallmark of beetles is that their forewings are hard, forming a protective shell over their back. Beyond that, beetles are incredibly varied in appearance and lifestyle, and can be found on both land and water. There are more than 170 different beetle families, some of the largest being true weevils, scarab beetles, leaf beetles, ground beetles, rove beetles, longhorn beetles and jewel beetles. All in all, there are around 380,000 known beetle species worldwide.

      The wasp order (Hymenoptera) consists of familiar insects such as ants, bees, bumblebees and stinging wasps, including many species that are social and live in colonies containing hordes of female workers and one or more queens. The order also encompasses many lesser-known sawflies and a huge number of parasitic wasp species. So far, we have identified more than 115,000 species in this order, but the number is rising steadily and this is probably the largest order of insects.

      Butterflies and moths (of the Lepidoptera order) have wings covered in tiny scales arranged like roof tiles. There are more than 170,000 Lepidopteran species in the world, but many are small and unassuming. The best known are of course butterflies – comprising around 14,000 large, diurnal (as opposed to nocturnal) species that are often beautifully coloured and patterned. The nocturnal species are known as moths.

      Flies, or Diptera, include not only species we commonly call flies, like blow flies and horseflies, but also mosquitoes, gnats and crane flies. Their Latin name derives from the fact that they have only two wings (di means two, ptera means wing), whereas insects normally have four, as mentioned earlier. In Dipterans, the hindwings have been repurposed as small, club-shaped gadgets that help them achieve balance in flight. We know of at least 150,000 species of Dipterans worldwide.

      Most people are less familiar with the order of true bugs (Hemiptera), even though it encompasses more than 80,000 species. The group includes a variety of different-looking insects, like shield bugs, stinkbugs, bedbugs, pond skaters, cicadas, aphids and scale insects. They all have beak-shaped mouths that serve as a kind of drinking straw they use to suck up their food – often sap from plants, although a few are predators or blood-suckers. So, although we commonly use the word ‘bug’ to describe any sort of tiny critter, the true bugs are a specific group of insects. True bugs of the most familiar suborder, Heteroptera, are similar to beetles in body shape, but are identifiable by triangular marks on their backs.

      And just so you know: spiders aren’t insects. They belong to the same phylum, arthropods, but a separate class, arachnids, which they share with other creatures such as mites, scorpions and harvestmen (known as ‘weaving women’ in Norwegian because they move two of their eight legs as if they were pushing a shuttle to and fro across a loom).

      Millipedes, centipedes and wood lice aren’t insects either. To take the simplest hallmark, they all have too many legs and belong to various other groups of invertebrates. Nor are the super-cute springtails insects, despite having six legs, although they are nearly insects. That said, insect researchers are huge fans of a teeming, multi-legged community, so springtails and arachnids are often allowed into the fold when we discuss insects anyway. That is true in this book too.