Insects – physical characteristics
Insects can be large – like the 130 mm wingspan of the kapokapowai/bush giant dragonfly – or tiny – like the 2 mm namu/West Coast blackfly. Insects can be beneficial like the honey bee or a pest like the clover root weevil. They can be daytime fliers like the kahukura/red admiral butterfly or nocturnal fliers like the pūriri moth.
New Zealand giraffe weevil
A male giraffe weevil (Lasiorhynchus barbicornis) guards a female giraffe weevil. The males have antennae at the tip of their snout-like mouthparts. The females use their mouthparts to bite holes in tree trunks to lay eggs. Their antennae are located further up the head so they are not damaged during this process. Learn more about these amazing creatures in this animated video on YouTube.
Regardless of their size, behaviour or habitat, insects worldwide have common physical characteristics.
The exoskeleton
Insects have an outer skeleton called an exoskeleton. This hard covering protects and supports the body. It is made up of two layers. The outer layer is thin, waxy and water resistant. The inner layer is much thicker and is made of chitin. Depending on the insect, the exoskeleton can be quite hard and rigid – like that of a cockroach – or less so when the insect is in its larval (caterpillar) stage or if it has a soft body – like a blue blowfly.
The exoskeleton is non-living so it cannot grow with the insect when it is in its larval form or as an adult. Insects shed their old exoskeletons, expand to a larger size and then wait for the new exoskeleton to harden. This is called moulting, and it happens many times during an insect’s lifespan. One of the most common signs of moulting comes in the spring when we find cicada shells (exoskeletons) on trees and fences.
Cicada exoskeleton
Cicada nymphs shed their skin, leaving the exoskeleton behind. The adult cicada emerges from the skin and later flies away.
The head
The head is the top section of an insect’s body. Many of the insect’s sense organs are located here. A pair of antennae allow insects to smell, feel the surface of an object, sense hot and cold, listen to sounds or detect movement. Insects have a pair of compound eyes – each made up of thousands of lenses. Compound eyes provide a wider field of vision, which is really useful for flight or when hunting prey. Insects may also have simple eyes called ocelli, which consist of single lenses. They allow insects to sense light and dark. You can see three ocelli on the head of the wasp in this image – they look like black bumps.
A common wasp
Insects have paired antennae so they can smell in stereo. They can detect the smallest of concentrations of scent. Pictured is the common wasp (Vespula vulgaris).
The insect’s mouthparts are also on the head. Insects have evolved mouthparts for a variety of purposes. Insects such as beetles and grasshoppers have mouthparts that allow them to chew. Butterflies and moths have a proboscis that allows them suck liquids. Insects like mosquitoes have mouthparts that pierce their food, while houseflies sponge their food, dissolving it in saliva before sucking it up.
The thorax
The thorax is an insect’s middle section. It consists of three segments. Each segment has a pair of jointed legs. An insect’s legs are adapted to suit their lifestyle and habitat. They include:
long narrow legs made for running and fast movement (beetles and cockroaches)
muscular hind legs made for jumping (grasshoppers and fleas)
hunting forelegs made for grabbing and holding prey (praying mantises)
swimming legs made for easy movement through water (water boatmen)
broad, flat forelegs made for digging burrows (mole crickets).
If the insect has wings, a pair of forewings and a pair of hind wings are attached to the thorax. Like our native birds, Aotearoa New Zealand has a significant number of wingless or flightless insects. For example, the honi/mole cricket is the only wingless mole cricket in the world!
Camouflaged hind wing of a yellow admiral
The upper sides of native butterfly wings are often colourful, but the hind wings (underside) are dull and patterned so they are camouflaged when their wings are closed.
The abdomen
The abdomen is the rear or final section of the insect. This is where the digestive, excretory and reproductive organs are located. The abdomen has 9–11 segments. Each segment has a pair of spiracles or openings in the exoskeleton. Insects open the spiracles to allow air in but close them to prevent water loss. Aquatic insects have similar methods to prevent water from entering the spiracles.
Related content
Explore What’s so special about insects?, Insect taxonomy and Aquatic insect life to find out more about insects.
Discover more of our resources on insects, or explore the range of content under our invertebrates topic.
Download these posters from the New Zealand insect cards project:
In the Connected article City of bugs, students teamed up with a scientist to find out which ecosystem in their city had the most invertebrates.
Learn about bringing insects into your classroom in our PLD webinar All about insects featuring entomologists Dr Chrissie Painting and Tom Saunders.
Activity ideas
Practise your knowledge of insects’ physical characteristics with Label the wētā and Label the cicada used in the Label the insect activity.
Your students can learn more about how the Linnaean classification system works with the activity Insect mihi. Students write a formal introduction for an insect species of their choice, including information about the insect’s relationship to other animals and also the land.
This activity shows you how to collect moths, and this activity tells you how to rear them to observe their life cycle.
Useful links
Visit our We love bugs! Pinterest board with links to resources and community activities.
See Manaaki Whenua – Landcare Research's online What is this bug? – a handy guide to common invertebrates of New Zealand.
Visit the New Zealand Entomological Society website.
