Invasive pests are an increasing concern for homeowners throughout the St. Louis area, as they can do serious damage or even mortally wounding a tree before their effects are apparent.

Unlike native insects, invasive species often arrive without natural predators to keep them in check. That allows their populations to grow quickly, putting stress on trees and, in some cases, killing them over time. In the Midwest, several invasive pests have become ongoing threats, making it important for homeowners to know what to look for.

Why Invasive Pests Are a Growing Problem

The spread of invasive pests has accelerated in recent years, largely due to global trade and the movement of firewood and plant materials. Once introduced to a new area, these insects can move rapidly from tree to tree.

St. Louis and the surrounding region are especially vulnerable because of the wide variety of tree species found in residential neighborhoods. When a pest targets a specific type of tree, and that tree is common locally, the impact can be devastatingly quick and widespread.

The challenge is that early signs of infestation are often subtle. By the time visible damage appears, the tree may already be under significant stress.

Three of the Most Common Invasive Pests in the St. Louis Area

While new threats continue to emerge, a few well-known invasive pests are already established in Missouri and remain a concern for homeowners.

Emerald Ash Borer (EAB)
This small, metallic-green beetle has devastated ash tree populations across the Midwest. It attacks from the inside out, disrupting the tree’s ability to transport water and nutrients.

Signs of infestation include:

• Thinning canopy and dieback in upper branches
• D-shaped exit holes in the bark
• Increased woodpecker activity
• Vertical bark splits

Bagworms
Bagworms are highly visible and commonly found on evergreens, though they can affect deciduous trees as well. They form small, cone-shaped “bags” that hang from branches.

Left untreated, heavy infestations can defoliate and weaken trees significantly.

Japanese Beetles
These insects feed on leaves, often leaving behind a skeletonized appearance. While a single season of feeding may not kill a tree, repeated damage can reduce overall health and vigor.

A Growing Concern: What’s Next?

In addition to established threats, other invasive pests are being closely monitored as they expand their range.

The spotted lanternfly, for example, has been spreading across parts of the eastern United States. While not yet widespread in Missouri, it’s something tree care professionals are keeping a close eye on due to its potential impact on a variety of plant species.

Staying informed about emerging pests is an important part of protecting your landscape over the long term.

Signs Your Trees May Be Affected

Because infestations often begin quietly, it’s important to watch for changes in your trees over time.

Some common indicators include:

• Leaves that appear chewed, skeletonized, or discolored
• Thinning canopy or early leaf drop
• Unusual growths, holes, or markings on bark
• Increased insect or bird activity around a specific tree
• Branch dieback, especially in the upper canopy

These symptoms don’t always point directly to invasive pests, but they are worth investigating as early intervention can, in many cases, go a long way toward saving a tree from extreme damage or worse.

What Homeowners Can Do

There are a few practical steps homeowners can take to reduce the risk of infestation and catch problems early.

• Avoid moving firewood from one location to another, as it can carry insects
• Inspect trees regularly, especially during the growing season
• Maintain tree health through proper watering and mulching, as healthy trees are more resilient
• Contact a certified arborist if you notice any signs of potential infestation.

It’s also helpful to know what species of trees you have on your property, as certain pests target specific species of trees.

When to Call a Professional

If you suspect your trees may be affected by invasive pests, timing matters. Early intervention can make a significant difference in whether a tree can be treated and saved or lost.

A professional tree service can:

• Identify the specific pest involved
• Evaluate the extent of the infestation
• Recommend treatment options, if appropriate
• Advise on whether removal is necessary in severe cases

In some situations, treatment can protect not only the affected tree but also nearby trees at risk.

Protecting Your Landscape Over Time

Invasive insects aren’t going away, but with awareness and proactive care, their impact can often be managed.

By keeping an eye out for invasive pests and addressing issues early, homeowners can help preserve the health and beauty of their trees for years to come.

If you’ve noticed changes in your trees or want help identifying potential pest issues, Hansen’s Tree Service is here to help! Contact us to schedule an evaluation and get expert guidance on the best next steps.