Question: What do I need to know to identify insects in my garden?
Learning to identify and manage insect populations in your garden can seem a daunting task. Winter is a good time to learn the basics of insect ID, so you will be ready to identify insects in the growing season!
Scientists have identified more than 1 million insect species, but believe there are at least another 4+ million still to be recorded! Only 3% of insects are considered pests; most are beneficial or at least harmless to humans.
What is an insect?
In its adult form an insect has a hard, shell-like covering on the outside of its body, three main body parts (head, thorax and abdomen), a pair of antennae on top of its head, and three pairs of legs.
You can learn techniques to aid in identifying the insects that inhabit your garden and help to distinguish the beneficial ones from the destructive ones. This makes it much easier to determine any necessary control options for destructive insects as well as help in understanding how to utilize the beneficial insects. Try to learn environmentally friendly techniques to manage or even increase the insect population in your little ecosystem.
Asking the Right Questions
Think of yourself as a ‘bug’ detective and ask all the right questions to help identify the insect. What does the insect look like? What color is it? How large is it? What distinguishing features does it have? Where did you find it? What type of damage did the insect do? Or, if it is a ‘good’ insect, is it preying on other insects? For example, if you find a ladybug or two around a leaf with aphids, the ladybug is making a meal of them. In what part of its life cycle is the insect? For example, a caterpillar is the larva (immature form) of a butterfly or moth.
And, no detective is complete without a good magnifying glass with at least 10x magnification and a guide book such as Garden Insects of North America: The Ultimate Guide by Whitney Cranshaw or an online resource such as the Bug Guide.
Recognizing Body Parts of Insects
Body parts are important in the identification of insects. Insects that have similar body parts and characteristics are often grouped together, which can make identification a little easier. For example, grasshoppers, crickets, and katydids all have legs that are used for jumping. The form, size, and function of body parts give clues to identifying the insect.
1) The head contains the eyes, mouthparts and antennae. The antennae can be one of the most distinctive features of an insect and are used for smell, touch, and/or hearing. Mouthparts are important too because they vary in form and function and can indicate the type of feeding damage. Most mouthparts fall into two categories – those for chewing and those for piercing and sucking.
2) The thorax, where the wings and legs are attached, has three segments. Most adult insects have two pairs of wings, which are attached to the second and third segments. Legs and their functionality are also frequently used in insect identification. Depending on the type of insect, they may use their legs for walking, jumping, digging, grasping, feeling, swimming, carrying loads, and/or building nests.
3) Finally, the abdomen may have many segments, but most often, they are difficult to see when they are short or covered by wings.
Understanding Insect Life Cycles
To complicate the identification process, you need to know about insect life cycles. For some insects, the adults and juveniles do not resemble each other. It may also be that an insect in one stage causes damage, while in another stage it does not. A swallowtail butterfly is beautiful and a beneficial pollinator; while the caterpillar that develops into a butterfly will hungrily consume a plant. If you kill the caterpillar, you lose a future pollinator.
The life cycles of insects fall into three main categories:
1) Without metamorphosis – insects increase in size throughout their life cycle, but do not change their body structure and are wingless. The insect nymph looks like a smaller version of the adult with similar diets and habitats. An example is a silverfish.
2) Gradual or incomplete metamorphosis (change in form) – these insects maintain the same basic characteristics but increases in size. They have three stages: egg, immature and adult. Another difference between the adult and the immature insect is that it does not develop fully functioning wings until adulthood. This is the most common type of metamorphosis in insects. An example is a cricket.
3) Complete metamorphosis – these are insects that go through four distinct stages: egg, larva, pupa, and adult. The immature larva and the adult differ greatly in appearance, diet, and habitat. The changes occur during the metamorphosis of the pupa stage. These are the most evolutionary advanced insects. An example is a butterfly.
Knowing the Insect’s Scientific Name
In common language, sometimes there is more than one name used for the same insect. And, sometimes the same name is used to describe more than one distinct insect. That can drive entomologists (scientists who study insects) crazy!
Scientific taxonomy provides a system for naming and classifying insects by certain characteristics. Once you learn those characteristics, it is easier to narrow down your choices, using the classification system in the reference guides or online websites. If all else fails, you can call or email the Virginia Cooperative Extension Horticultural Help Desk for help with insect identification.
Good Bugs versus Bad Bugs
Finally, get to know the good insects in your garden. Among them are pollinators, predators, decomposers, and parasitoids. The pollinators, such as bees and butterflies, are needed for the production of crops and the pollination of flowers. Predators, such as ladybugs, lacewings, assassin bugs, praying mantis, and dragonflies catch and eat other insects. Decomposers, such as beetles, wasps, and ants, aid in the decomposition of dead organisms. Parasitoids are insects which live on or in another host insect, getting their food from the host and eventually killing it. The female Glyptapanteles wasp inserts its eggs in a caterpillar, and once the eggs hatch, the larval wasps devour the caterpillar.
And, remember that insecticides do not discriminate between good bugs and bad bugs, so try to avoid their use by employing cultural techniques as well. Select resistant varieties of plants, inspect plants before you buy them, pick off and kill bad insects by hand when possible, remove old plant debris at the end of the season, and tolerate some amount of insect damage within your garden. There is a useful guide on beneficial garden insects by Jessica Walliser called Good Bug, Bad Bug, Who’s Who, What They Do, and How to Manage Them Organically.
If you must use a pesticide, be sure to use a product recommended in the Virginia Cooperative Extension, Pest Management Guide: Home Grounds and Animals, 2020. Remember to read and follow the directions on the pesticide label exactly. The label is the law.
References:
Good Bug, Bad Bug, Who’s Who, What They Do, and How to Manage Them Organically, Jessica Walliser, St. Lynn’s Press, 2008.
“Insect Identification,” Scott Schell & Dr. Alex Latchininsky, Entomology, University of Wyoming, 2007.
Insect Identification Lab, Department of Entomology, College of Agriculture and Life Sciences, Virginia Tech.
