10 Ways to Identify An Insect

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Is It An Insect?

Mosquito identification for malaria eradication
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When you encounter a new insect in your backyard, you want to know what it’s likely to do while it’s there. Is it going to eat one of your garden plants? Is it a good pollinator for your flowers? Will it lay eggs in the soil, or pupate somewhere? You can learn some things about an insect just by observing it for a while, of course, but that’s not always practical. A good field guide or website may provide information about the mysterious visitor, but you need to know what it is first.

Identifying an Insect

So how do you identify an insect you have never seen before? You collect as much information as you can, looking for clues that will place the insect in a taxonomic order. Ask yourself each of the following questions about your unidentified insect. You might not be able to answer all of them, but any information you gather will help narrow down the possibilities. First, be sure you are looking at an insect, and not another arthropod cousin. 

To be sure you're really looking at an insect, ask yourself these three questions:

1. Does it have six legs?

All insects do.

2. Are there three distinct body regions—head, thorax, and abdomen?

If not, it's not a true insect.

3. Do you see a pair of antennae?

These are another necessary insect feature.

Also, note that most—but not all—insects have two pairs of wings.

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Is the Insect An Adult?

Yellow butterfly hatching
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The taxonomic orders are based on the adult forms of insects. If you have a caterpillar, for example, you won’t be able to use most guides or dichotomous keys. There are ways to identify immature insects, but for this article, we are only looking at adults.

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Where Does It Live and When Is It Active?

Honey bee searching for nectar on a vivid magenta flower
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Insects live in certain climates and habitats. Many insects decompose plant matter, for example, and are typically found in soil, leaf litter, or in rotting logs. Tropical regions of the world have many unique species of butterflies and moths that you will not find in a temperate zone. Make a few notes about where you found or observed the insect.

See if Your Insect Prefers Specific Plants

Some insects have important relationships to specific plants, so the plants in the area might be clues as well. A wood borer is often named for the tree it inhabits and feeds on; knowing the name of the tree can lead you to a quick identification of the insect.

Note When Your Insect is Most Energetic

Like other animals, insects may be diurnal or nocturnal, or a combination of both. Butterflies require the sun’s warmth of to fly, and so are active during the day.

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What Do the Wings Look Like?

Dragonfly wing, Maine.
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The presence and structure of the wings may be your best clue to identifying an insect. In fact, many insect orders are named for a specific wing characteristic. The order Lepidoptera, for example, means “scaly wings.” If you plan to use a dichotomous key to identify the insect, you will need information about the wings to complete the key.

Check Your Insect's Wings for Distinguishing Features

Here are some key details to observe when looking at an insect’s wings:

  • Does the insect have wings, and if so, are they well developed?
  • Do you see one or two pairs of wings?
  • Do the forewings and hindwings look similar or different?
  • Are the wings leathery, hairy, membranous, or covered in scales?
  • Can you see veins in the wings?
  • Do the wings appear to be larger than the insect’s body, or about the same size as the thorax?
  • How does the insect hold the wings when resting—folded flat against the body, or vertically above the body?
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What Do the Antennae Look Like?

Timberman beetle (Acanthocinus aedili) showing antennae which are four times the length of its body, central Finland, May.
Jussi Murtosaari/Nature Picture Library/Getty Images

Insect antennae come in a variety of forms, and are an important characteristic to examine when trying to identify an insect. Some insects, like Proturans, lack antennae. If the antennae are not clearly visible, use a hand lens to get a better look. Do they appear threadlike or are they club-shaped? Do the antennae have an elbow or bend? Are they feathery or bristled?

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What Do the Legs Look Like?

Female European praying mantis (Mantis religiosa) portrait, Sardinia, Italy, September 2008.
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An insect’s legs are adaptations that help it move, eat, and survive predators. Aquatic insects sometimes have legs that look like boat oars, and as you might expect, these legs are made for swimming. Terrestrial insects like ants spend most of their time walking, and have legs designed for quick movement on the ground. Look at a grasshopper’s legs. The third pair is folded and much larger than the others; these powerful legs propel the grasshopper through the air and away from predators. Some insects are predators themselves, and have front legs designed for catching and grasping smaller insects.

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What Do the Mouthparts Look Like?

Honeybee on Daisy flower - Northern Vosges
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The insect world is diverse, and that diversity is well represented by the different types of mouthparts insects may have. There are insects that eat leaves, some that chew on wood, others that drink sap or nectar, and even some that prey on other insects.

Note Whether the Mouth is Designed for Chewing, Piercing, or Just Drinking

Many flies feed on sugary foods, and have a sponge-like mouth for collecting sweet fluids. Butterflies drink nectar and have a coiled tube called a proboscis, which uncurls to reach into flowers. Insects that feed on plant matter have chewing mouthparts, designed to break down plant fibers. Predatory insects, such as mantids, also have chewing mouthparts. Some insects, like weevils and aphids, specialize in drinking plant fluids. They have mouthparts that pierce the plant and then suck the fluids from inside.

If you can, use a hand lens to take a closer look at the insect's mouthparts, and try to discover what kind of mouthparts your mystery insect has.

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What Does the Abdomen Look Like?

Green Dock Beetle (Gastrophysa viridula) female with huge abdomen swollen with eggs.
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The abdomen is the third region of the insect body. Like all arthropods, insects have segmented bodies. The number of abdominal segments can vary between insect orders. The abdomen may also have appendages that are clues to the identity of the mystery insect.

Look at the Insect's Abdominal Segments

The number of abdominal segments varies from six to eleven. For example, silverfish usually have eleven segments, while springtails only have six. If they are visible, try counting the segments.

Look for Appendages at the End of the Insect's Abdomen

Your mystery insect may have an obvious “tail” at the end of the abdomen, or what appears to be a set of pincers. These structures are touch organs called cerci that help the insect feel. Earwigs have modified cerci that function as forceps. Three-pronged bristletails are named for their three cerci.

Note the Size and Shape of the Insect's Abdomen

Note the size and shape of the abdomen as well. Is the abdomen long and slender (like in mayflies)? Does it look swollen compared to the thorax? Some identification keys use these characteristics as well as the others you have already observed.

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What Color Is the Insect?

Large Red Damselfly, Pyrrhosoma nymphula on an Iris leaf above a pond.
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Insects can be quite colorful, with distinct markings that are unique to a certain species.

Note Any Colors and Patterns on the Insect's Wings

You cannot identify a butterfly without knowing the colors and patterns on its wings. Some beetles have iridescent forewings; others display spots or stripes. But it’s not just insect wings that come in every color of the rainbow. Their bodies may also have unique and colorful markings. Monarch butterflies are known for their orange and black wings, but many people don’t notice the white polka dots on their black bodies.

Note Any Patterns on the Insect's Body

Note any colors and patterns on the wings and the body of your mystery insect. If there are dots or stripes, try to count them. Some species mimic the colors of others as a means of fooling predators, so your observations need to be as specific as possible.

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How Does It Move?

Roesel's Bush Cricket (Metrioptera roeselii) male leaping
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It's helpful to note how your mystery insect moves, whether in captivity or in the wild.

See if Your Insect Flies, Jump, Walk, or Wriggles

If you observe the insect flying, you know it is a winged insect and can eliminate at least four insect orders (the wingless insects) from your guesses. Some insects, like grasshoppers, prefer to propel themselves with their legs but are capable of flying when necessary. Mantids walk unless threatened, and then they will fly as well. Springtails are named for their ability to spring or launch themselves into the air. Even if these traits don’t give you definitive answers to an insect’s identity, making notes on their movement patterns will teach you something about how that insect lives.