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Learn to Identify Garden Insects – Good and Bad

Alyce Neperud, Dakota County Master Gardener

We know that most insects in our garden are beneficial. But when we find insect damage on our beloved flowers, vegetables and fruits, it’s hard not to focus on the damaging insects. A good gardening practice is to keep abreast of the latest research on how to attract good insects and adopt pest management practices to minimize damage from the “bad” insects. By seeking out research-based information on good and bad insects, you can learn about potential damage and a range of control options to make well-informed decisions about managing the pests in your Minnesota garden. Read this article to learn more about good and bad insects and how to tell the difference.

Learn to Identify Garden Insects – Good and Bad
Some common pests and how to identify them

Leaf Lily Beetle

While inspecting my garden in late May, I noticed holes in the Asiatic lily leaves and some red beetles. I confirmed the insect to be a Leaf Lily Beetle, a non-native pest. I learned most of the damage is done by the larva so I inspected the lilies again. As expected, I found muddy brown globs. I cleaned the larva off, removed the beetles and limited further damage by frequent inspection and manual removal of the pest.

Leaf Lily Beetle

Check out the following articles to learn more about this pest, its lifecycle and control options:

Cabbage Worm

While working with master gardeners at a local vegetable trial garden, I learned that each year the cabbage is damaged by caterpillars. The first sign of the pest in the garden is a white butterfly with a black spot on each wing. The butterfly and the larva are a match to the imported cabbageworm. 

Cabbage worm

This pest can be difficult to control manually once established and the damage reduces the amount of usable produce. To attempt to control the pest this year, we installed a mesh cover over the cabbage when the small plants were transplanted into the garden. The intent is to minimize damage with early intervention so that the butterflies are not able to lay their eggs. The results for this year are pending but sometimes a new approach is worth trying.

Check out the following articles to learn more about common vegetables pests, lifecycles, expected damage and control options from the UMN Extension:

Shrub Rose Pests

Three pests attack my shrub roses every year. The damage starts in early May with white spotting on the lower leaves, an indication of sap sucking - Rose Leafhopper

Rose Leafhopper and leaf damage

In June I observe green caterpillar-like larvae munching on the leaves - the Rose Sawfly larva (also known as Roseslug). 

Leaf damage from Rose Sawfly
Adult Rose Sawfly

In late June, beetles can be seen destroying the rose blooms - the Japanese Beetle

Japanese Beetle

Despite all of this pest activity, the roses can be enjoyed most of the season with some manual control.  I squash the leafhoppers early if there is significant damage. I watch for the appearance of the Roseslugs and squash them or drop them into soapy water. This year I also began looking for the sawflies to see if I could disturb them and prevent them from laying their eggs and thus minimize the Roseslug problem. The Japanese beetles are the most destructive and because they are relentless, I knock them into soapy water as frequently as is feasible. The best news is that the pests are mostly gone when the roses bloom a second time in late summer.

Check out the following articles to learn more about rose pests, lifecycles and control options:

Sawfly and its larvae, Roseslugs are located under Deciduous Trees and Shrubs.(UMN Extension)

Rose pests. (UKY, includes Japanese Beetle, Roseslug, Rose Leafhopper and others)

What about the good insects?

The insects that damage our plants grab our attention but we need to remember that most insects in our gardens are beneficial and play a vital role in the ecosystem.

Insects pollinate a wide variety of fruits, nuts, vegetables, and native plants. Insects also decompose plant and animal material, are used in medicine and research and they are an essential food source for many birds, mammals and other insects. An apple exists only when the flower is pollinated. A butterfly exists only when the caterpillar is allowed to mature to adult stage, with essential food sources and the correct host plant.


Insects that pollinate include wild and domesticated bees, flies, wasps, moths, butterflies and more. Did you know that flies are second to bees in pollination? 

  • The syrphid fly appears to be a small bee but is actually a “hover fly” that moves about quickly and feeds on nectar and pollen. I found this pretty little fly hovering and feeding on cranesbill geranium, shrub rose and columbine flowers in my garden. Look for it! Unlike bees and wasps which have two pairs of wings, the syrphid fly has a single pair. It does not sting or bite.

Syrphid fly
  • Butterflies are incredibly beautiful and fun to watch, make it your goal to learn about some new butterflies to attract to your garden with nectar and larval host plants for butterflies. Butterfly Gardening. (UMN Dept. of Entomology)

  • Bumblebees are a joy to watch in addition to the serious pollination work they do.  This UMN BeeLab page includes a field guide to identify Minnesota Bumblebees.



Some insects are beneficial because they feed on other insects and frequently it is not the adult that provides the most benefit. This is why understanding the insect’s lifecycle and what it looks like in different stages can help us better appreciate their value. 

  • Lacewings, in their wingless immature state, eat other insects.

  • Lady beetles are beneficial because they feed on insects, nectar and pollen. Asian lady beetles are a bit larger and are a nuisance if they get in your house, but they are otherwise beneficial because they also feed on soft body pests. Both types have alligator-like larvae, quite different from the domed, hard, round to oval shaped adult beetle.

  • Wasps. There are many types of wasps that help control garden pests. For example, the parasitoid wasp is beneficial because it lays its eggs on pests such as the aphid or imported cabbage worm, to feed on the host. These wasps are tiny so don’t expect to identify them but you may see small eggs or larva on the host.

  • The Syrphid fly is not only a pollinator but also feeds on small insect pests.  

For more on these and other beneficial insects in Minnesota:  UMN extension Beneficial Insects .

Tips for successfully identifying good and bad insects

In order to know whether you need to take steps to control an insect, you need to successfully identify it. Try this process:


  • Be proactive by inspecting plants and watching for insects when they are expected to appear.

Gather Information

  • Take a picture please! This will help you recall details when doing your research

  • What type of insect? Does it appear to be a beetle, butterfly or moth, caterpillar, grub or other? Note size, color, markings, # of wings, etc.

  • Where did you find it? Insect pests tend to be specific to certain plants. Is it on a plant or in the soil? 

  • Is there any feeding damage? Sometimes you will have to rely on the damage to do your inquiry when the insect is not present. 

  • What time of year is it? Insects emerge at different times of the year, some have annual cycles, others have multiple cycles in one season. 

Take the information you have gathered and go to reputable sources to identify the insect and how to manage it.

Anticipate and Plan Accordingly

  • When you’ve learned the lifecycle and the best time to interrupt the lifecycle, you can be more strategic about solving a problem.

Keep up the good gardening!

We all strive for a beautiful flower garden and healthy fruits and vegetables. So, it is important to identify and control threats from damaging insects early. Try to develop a more observant eye and know when to look; anticipate and plan accordingly. Get to know good insects, learn to attract and protect them!  Many resources are available to help you satisfy your curiosity about an insect, or help you solve a problem. But don’t hesitate to ask for help if you get stumped.

Additional References on Pollinators

Photo Credit: Alyce Neperud (1, 3, 7, 8), University of Minnesota Extension (2, 4, 5, 6, 9)

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