Michigan’s natural beauty faces an unprecedented threat from invasive insects that cause over $50 million in agricultural and forestry damage annually.
These non-native species, accidentally introduced through global trade and travel, now threaten your trees, gardens, and local ecosystems in ways that native predators cannot control.
Understanding how to identify invasive insects in Michigan protects both your property and the state’s natural resources.
This guide provides the essential knowledge you need to recognize, report, and respond to these destructive pests before they establish permanent populations in your area.
1. Emerald Ash Borer
The Emerald Ash Borer (Agrilus planipennis) stands as Michigan’s most destructive invasive insect, having killed tens of millions of ash trees since its 2002 discovery. The pest is thought to have been established in Michigan for at least 10 years by the time of its discovery, making early detection crucial for remaining healthy ash populations.
Identification Features:
- Metallic green adult beetles, 1/2 inch long
- D-shaped exit holes in bark
- S-shaped larval galleries under bark
- Crown dieback starting at the top of trees
Damage Signs: You’ll notice thinning canopy, increased woodpecker activity, and bark splits revealing distinctive galleries. Infected trees typically die within 2-4 years of initial infestation. The emerald ash borer affects all native ash species, making species identification critical for property owners.
Pro Tip: Check ash trees annually between May and September when adult beetles are most active. Early treatment with systemic insecticides can save valuable trees.
2. Spotted Lanternfly
The Spotted Lanternfly (Lycorma delicatula) represents Michigan’s newest invasive threat, with Michigan’s first detection confirmed in Monroe County in 2024. This colorful planthopper poses significant risks to agriculture and natural areas.
Life Stage Identification:
- Nymphs (Spring-Summer): Black with white spots, red patches as they mature
- Adults (Late Summer-Fall): Gray-brown wings with black spots, bright red underwings
Host Plants and Damage: Spotted lanternflies feed on over 70 plant species, including grapes, apples, and hardwood trees. They excrete honeydew that promotes sooty mold growth, weakening plants and creating sticky surfaces on cars and outdoor furniture.
Key Takeaway: Report any spotted lanternfly sightings immediately to prevent establishment of breeding populations.
3. Asian Longhorned Beetle
The Asian Longhorned Beetle (Anoplophora glabripennis) threatens Michigan’s hardwood forests and urban trees. With a shiny, black body flecked with irregular, white blotches and long antennae with alternating black and white bands, this beetle is distinctive among Michigan’s insects.
Identification Characteristics:
- Glossy black body with irregular white spots
- Antennae 1.5-2 times body length with black/white bands
- Body length: 3/4 to 1-1/4 inches
- Six legs with blue-tinged feet
Tree Damage Indicators: Round exit holes about pencil-diameter size appear in trunks and branches. You’ll also find shallow oval scars where females chewed egg-laying sites and sawdust-like material called frass around tree bases.
4. Brown Marmorated Stink Bug
The Brown Marmorated Stink Bug (Halyomorpha halys) has become a significant agricultural pest across Michigan, affecting both crops and becoming a household nuisance when seeking winter shelter.
Physical Description:
- Shield-shaped brown body with marble-like patterns
- 5/8 inch length with distinctive white bands on antennae
- Alternating light and dark bands on wing edges
- Emits foul odor when disturbed or crushed
Agricultural Impact: This pest damages over 100 crop species including soybeans, corn, tomatoes, and tree fruits. Feeding creates dimpled, discolored areas on fruits and vegetables, making them unmarketable.
5. Japanese Beetle
The Japanese Beetle (Popillia japonica) is widespread throughout Michigan, causing extensive damage to lawns, gardens, and agricultural crops during its summer feeding period.
Adult Beetle Features: Adult beetles are about 3/8 inch in length and have a bright, metallic green head and body and metallic brown wings, making them easily recognizable during peak activity from June through August.
Damage Patterns: Adults skeletonize leaves by eating tissue between veins, while larvae (grubs) damage grass roots. You’ll find adults congregating on preferred plants like roses, grapes, and linden trees.
Management Strategy: Hand-picking works for small infestations, while pheromone traps can reduce populations when placed away from valued plants. Japanese beetle management requires integrated approaches for effective control.
6. European Gypsy Moth (Spongy Moth)
The Spongy Moth (Lymantria dispar) continues threatening Michigan’s forests despite ongoing management efforts. This defoliator can strip entire forests bare during outbreak years.
Caterpillar Identification:
- Hairy, dark-colored caterpillars up to 2.5 inches long
- Five pairs of blue dots followed by six pairs of red dots
- Yellow and black striped head capsule
- Most active at night, hiding during day
Defoliation Impact: Spongy moth caterpillars defoliate trees, leaving trees vulnerable to diseases and other pests, which may lead to tree mortality. Preferred hosts include oak, aspen, and birch trees.
7. Hemlock Woolly Adelgid
The Hemlock Woolly Adelgid (Adelges tsugae) poses a severe threat to Michigan’s hemlock forests, particularly in the western and northern regions where these iconic conifers dominate.
Identification Signs:
- Small white woolly masses on hemlock branches
- Typically found at base of needles on undersides of branches
- Active year-round, most visible in spring and fall
- Causes needle drop and branch dieback
Forest Impact: Infested hemlocks show yellowing needles, reduced growth, and eventual death. These trees provide critical wildlife habitat and watershed protection, making adelgid control essential for ecosystem health.
8. Pine Shoot Beetle
The Pine Shoot Beetle (Tomicus piniperda) attacks pine trees throughout Michigan, causing shoot mortality and weakening tree defenses against other pests.
Beetle Characteristics:
- Dark brown, cylindrical beetles 1/8 to 1/4 inch long
- Create small round holes in pine shoots
- Active during warm periods in late winter and early spring
- Prefer stressed or weakened pine trees
Damage Assessment: Look for yellowing and browning shoot tips, especially on Scots pine and other two-needle pines. Heavy infestations can cause significant crown dieback and predispose trees to other problems.
9. European Corn Borer
The European Corn Borer (Ostrinia nubilalis) remains a major agricultural pest in Michigan, affecting corn production and extending into other crops.
Larval Description:
- Cream-colored caterpillars with brown heads
- Reach 1 inch in length when mature
- Create tunnels in corn stalks and ears
- Two generations per year in Michigan
Economic Impact: This pest causes millions of dollars in crop losses annually through stalk boring, ear damage, and secondary infections. Modern Bt corn varieties provide excellent control for most farms.
10. Cabbage White Butterfly
The Cabbage White Butterfly (Pieris rapae) affects cruciferous crops and garden plants throughout Michigan, making it a concern for both commercial growers and home gardeners.
Adult and Larval Identification:
- White butterflies with black wing spots
- Green caterpillars with faint yellow stripes
- Most active during warm, sunny weather
- Multiple generations per growing season
Garden Damage: Larvae feed on cabbage, broccoli, cauliflower, and related plants, creating large holes in leaves and contaminating harvested crops with frass and feeding damage.
11. Multicolored Asian Lady Beetle
The Multicolored Asian Lady Beetle (Harmonia axyridis) exemplifies how beneficial insects can become problematic when introduced outside their native range.
Variable Appearance:
- Colors range from yellow to red with 0-19 black spots
- Larger than native lady beetles
- Form large aggregations in fall seeking shelter
- Can bite and stain surfaces with yellow secretions
Nuisance Behavior: While beneficial for aphid control, these beetles become household pests when overwintering in homes. Integrated pest management approaches balance their benefits with nuisance concerns.
12. Western Corn Rootworm
The Western Corn Rootworm (Diabrotica virgifera virgifera) challenges Michigan corn producers through root damage and resistance to multiple control methods.
Adult Beetle Features:
- Yellow-green beetles about 1/4 inch long
- Long antennae and distinct coloration
- Active from July through September
- Feed on corn silks and pollen
Root System Damage: Larvae tunnel through corn roots, causing lodging, nutrient stress, and yield reduction. Crop rotation and resistant varieties provide primary management tools.
| Insect | Peak Activity | Primary Hosts | Key Damage |
|---|---|---|---|
| Emerald Ash Borer | May-September | All ash species | Tree mortality |
| Spotted Lanternfly | August-October | 70+ plant species | Honeydew, plant stress |
| Asian Longhorned Beetle | July-October | Hardwood trees | Branch/trunk damage |
| Japanese Beetle | June-August | 300+ plant species | Leaf skeletonization |
13. Lily Leaf Beetle
The Lily Leaf Beetle (Lilioceris lilii) specifically targets lilies and fritillarias, making it a significant concern for gardeners and landscapers.
Distinctive Features:
- Bright red adult beetles
- Black legs, antennae, and underside
- Orange-red larvae covered in dark excrement
- Overwintering adults emerge in early spring
Plant Damage: Both adults and larvae feed on lily leaves, flowers, and buds. Severe infestations can completely defoliate plants, preventing bulb energy storage for following years.
14. Elongate Hemlock Scale
The Elongate Hemlock Scale (Fiorinia externa) works in conjunction with woolly adelgid to threaten Michigan’s hemlock populations.
Scale Identification:
- Tiny, elongated brown scales on needle undersides
- Causes yellowing and premature needle drop
- Weakens trees, making them susceptible to other pests
- Difficult to detect without close inspection
15. Swede Midge
The Swede Midge (Contarinia nasturtii) poses an emerging threat to Michigan’s cruciferous crop production, requiring vigilant monitoring.
Damage Symptoms:
- Twisted, distorted plant growth
- Brown scarring on stems and leaves
- Stunted or killed growing points
- Most severe in cool, moist conditions
Common Mistake: Many growers initially mistake swede midge damage for herbicide injury or nutrient deficiencies, delaying appropriate management responses.
16. Chinese Elm Flea Weevil
The Chinese Elm Flea Weevil (Orchestes steppensis) damages elm trees through both adult feeding and larval mining activity.
Weevil Characteristics:
- Small, dark beetles that jump when disturbed
- Create shot-hole feeding damage on leaves
- Larvae mine between leaf surfaces
- Multiple generations per growing season
17. Sirex Woodwasp
The Sirex Woodwasp (Sirex noctilio) represents a potential future threat to Michigan’s pine forests, requiring early detection efforts.
Wasp Description:
- Large wasps up to 1.5 inches long
- Dark blue-black coloration with yellow-orange legs
- Females have prominent ovipositor
- Associated with fungal infections in pine trees
Forest Threat: This pest-fungus complex can kill healthy pine trees within 1-2 years. Monitoring programs use specialized traps to detect new introductions.
18. European Fruit Lecanium Scale
The European Fruit Lecanium Scale (Parthenolecanium corni) affects various trees and shrubs, causing branch dieback and reduced plant vigor.
Scale Features:
- Brown, dome-shaped scales on branches
- Produce honeydew leading to sooty mold
- Weaken plants through excessive sap removal
- Overwinter as immature scales on bark
