Colorado tree pests can wreak havoc on your trees – and it’s not just aesthetics that we’re concerned about. Many tree species on the Front Range are vulnerable to damage from a wide variety of insects. Dead or dying trees caused by infestation are more than just unsightly—they can pose serious hazards, from structural instability and fire risk to long-term ecological disruption.
Bug activity in Colorado tends to ramp up during the warmer months—often beginning as early as February. Knowing what to look for and understanding how to protect your trees is essential for maintaining a safe, healthy landscape. Preventative care is often the most effective defense against infestations that could compromise the health of your trees and your property.
Table of Contents
TL;DR: How Do I Know if My Tree Has a Pest Infestation?
Answer:
Types of Colorado Tree Pests & The Damage They Cause
Different types of Colorado tree pests can damage trees in a variety of ways. Aside from diseases, the main three types of pests are borers, bark beetles and moths.
Borers
Borers damage trees by burrowing into their trunks and branches, disrupting the cambium layer—the vital tissue that transports water and nutrients. When this layer is compromised, it can lead to dieback and weaken the tree, increasing its susceptibility to other diseases. In extreme cases, a severe borer infestation can result in the tree’s death.
Bark Beetles
Bark beetles harm trees by tunneling through the bark to create intricate tunnel systems. As they burrow, they form galleries for laying eggs, often within the phloem during mid to late summer.
Beyond the physical damage, bark beetles can also introduce harmful fungi—such as the pathogen that causes Dutch Elm Disease—which further undermines the tree’s health. Together, the tunneling and fungal infection disrupt water and nutrient flow, weakening the tree and potentially killing it if not addressed.
Moths
Unlike borers and bark beetles, moths and their caterpillars damage trees primarily through defoliation—feeding on the leaves or needles. This loss of foliage hinders the tree’s ability to photosynthesize and produce energy, gradually weakening it. The resulting stress makes the tree more vulnerable to other pests and diseases.
The Specifics: Which Bugs Should I Look for?
Identifying specific tree pests can be surprisingly tricky, even for experienced gardeners and landowners. Many invasive or damaging insects resemble harmless or even beneficial species, which can lead to misidentification and delayed treatment.
For example, the Six-Spotted Tiger Beetle closely resembles the Emerald Ash Borer (EAB), a highly destructive invasive species that targets ash trees. Similarly, Lilac Borers and Ash Borers, which tunnel into wood and damage the tree’s vascular system, can be mistaken for paper wasps because of their similar size and coloring.
Misidentifying these pests can lead to incorrect management strategies—or worse, ignoring a serious infestation entirely. When in doubt, it’s wise to consult a certified arborist or pest control professional who can help properly diagnose the issue and recommend targeted solutions.
Bark Beetles
- Mountain Pine Beetle
- Turpentine Beetle
- Douglas Fir Beetle
- Ash Bark Beetle
- Spruce/IPS Beetle
Borers
- Emerald Ash Borer
- Lilac/Ash Borer
- Banded Ash Borer
- Poplar Borer
- Peach Tree Borer
- Pinyon Pitch Mass Borer
Moths
- Pine Tip Moth
- Douglas Fir Tussock Moth
- Zimmerman Pine Moth
- Spruce Budworm
Historical Trends in Tree-Damaging Insects
While not all of the Colorado tree pests we list have ranked high on historic, nationwide outbreak lists, it’s imperative to understand the magnitude of effect that such a small thing can have in large numbers.
Mountain Pine Beetle
The Mountain Pine beetle is responsible for the devastation of millions of Lodgepole Pine trees over the period of just a few decades. They will attack most native pine species in Colorado, minus Pinion Pines.
- This native bark beetle affected approximately 80% of the pine forests in Colorado from 1996-2014
Emerald Ash Borer
The EAB beetle was discovered in Michigan in 2002. The beetle had not been previously seen in the United States, and it possibly arrived sometime in the 1990’s. Since then, the beetle has spread to states surrounding Michigan and into Quebec, Canada. It was likely transported to the United States on a cargo boat or plane carrying infected ash wood from Asia, its natural habitat. EAB has already killed tens of millions of North American ash trees.
judygva (back in town and trying to catch up), CC BY 2.0, via Wikimedia Commons
Spruce/IPS Beetle
Another native bark beetle, the Douglas-fir beetle continues to cause significant tree mortality in the state’s central and southern mixed-conifer forests, affecting about 8,000 acres of forests statewide last year. Douglas, Gunnison, Jefferson, Eagle, Pitkin and Custer counties have severely affected Douglas-fir stands and this beetle has depleted many of the largest trees in these areas over the past decade.
Gilles San Martin from Namur, Belgium, CC BY-SA 2.0, via Wikimedia Commons
Identifying Signs & Symptoms In Your Trees
There are usually tell-tale signs that your trees are harboring pests or disease. By knowing what to look for, you can quickly address the issue and often save your tree from irreversible damage. Some signs that should alert you to a pest problem include:
Frass/Boring Dust
Usually appears as reddish or yellowish sawdust-like material that accumulates around the base of the tree, in bark crevices, or near exit holes. It’s a byproduct of insect tunneling.
Forest and Kim Starr, CC BY 2.0, via Wikimedia Commons
Sap/Resin/Pitch
- Sap
- A generic term for fluid that circulates through the tree that contains water, sugars, nutrients etc.
- Resin
- Secreted by certain trees as a defense mechanism against insects and pathogens.
- Pitch
- Dried resin.
Galleries/Tunneling patterns under the bark
Larvae and borers create characteristic tunnels under the bark. These vary by species: some form S-shaped galleries, while others follow a linear or perpendicular pattern to the wood grain.
Exit/Ventilation Holes
- Exit holes:
- Often oval, round, or D-shaped (e.g., EAB), these indicate where the insect emerged after pupation.
- Ventilation Holes:
- Small, pinhole-sized openings created during the larval stage to allow airflow into tunnels and galleries.
Rob Young from United Kingdom, CC BY 2.0, via Wikimedia Commons
Reddish/Fading/Discolored/Wilting/ Thinning leaves or needles
Any of these symptoms can suggest insect damage or other stressors, such as disease, drought, or root issues. Observe changes across seasons and tree sections.
Branch dieback
Severe infestations can cut off nutrient flow, leading to the dieback of twigs or entire limbs.
Bark Splitting
Some Colorado tree pests, like the Turpentine beetle or Mountain Pine beetle may cause bark to crack or split due to internal damage and pressure from galleries.
Visible Pupal Skins
Some insects, like the Emerald Ash borer or the Lilac/Ash borer leave their pupal skins on the outside of the bark, near their exit holes.
Whitney Cranshaw, CC BY 3.0, via Wikimedia Commons
Fungi
Some infestations introduce or promote fungal growth, such as blue stain fungus or red/brown wood rot, which further weaken the tree.
Woodpeckers
Heavy woodpecker activity can signal the presence of insects beneath the bark, especially borers or bark beetles.
Changes in the leaves, needles, branches, or trunk of your tree can indicate the presence of pests or disease. If you notice unusual symptoms, inspect the tree closely for visible insects. You may be able to identify the pest yourself or collect a sample to show an arborist. Photograph discolored leaves or needles, and if possible, capture the insect. These details can help professionals diagnose the issue and recommend effective treatment.
Commonly Affected Trees
Pine
Spruce
Fir
Elm
Ash
Stone Fruit
Susceptible Trees
Certain trees are more vulnerable to insect damage from Colorado tree pests, especially those already under stress or recovering from prior issues. These include:
- Trees weakened by drought
- Trees with fire damage
- Trees stressed by nearby construction
- Recently transplanted trees
- Trees with existing wounds, diseases, or past injuries
Pests often target these compromised trees first. While some insects cause the initial damage, others act as secondary invaders, exploiting weakened trees after the fact.
Pest Prevention & Management Tips
Cultural Measures
- Diversify tree species to reduce widespread vulnerability
- Choose appropriate planting sites
- Support tree health through proper watering and fertilization
- Prune carefully—timing, location, and method matter, as open wounds can attract pests
- Remove infested trees or stumps to prevent the spread
- Acquire firewood locally to avoid introducing non-native pests
Chemical Controls
- Use preventative sprays or targeted pest control when appropriate
- Consider pheromone baiting for certain beetle species
Natural Predators
- Encourage or protect natural predators like:
- Woodpeckers
- Clerid beetles
- Jumping spiders
Consequences of Tree Damage
Tree Death
Colorado tree pest infestations can cause girdling, which cuts off the flow of water and nutrients, leading to the eventual death of the tree. This can also affect nearby trees, causing a broader impact on your landscape.
Falling Limbs or Trees
Internal damage from pests weakens branches and trunks, increasing the risk of sudden breakage, especially during storms, high winds, or snowfalls. This can pose significant danger to people, homes, vehicles, and power lines.
Increased Fire Risk
Dry, dead wood from infested trees is highly flammable. In forested areas or during drought conditions, these trees can become fuel for wildfires, exacerbating the fire hazard.
Property Damage
Falling trees or limbs can cause expensive damage to buildings, fences, roofs, and vehicles. Even a single large limb can cause thousands of dollars in repairs.
Spread of Pests
Infected trees can serve as breeding grounds for invasive pests, allowing them to spread to healthy trees nearby—amplifying the damage across entire neighborhoods or forests.
Loss of Habitat
Trees provide shelter and food for birds, insects, and other wildlife. When trees die, it can disrupt local ecosystems and biodiversity.
Soil & Water Issues
Dead trees no longer stabilize soil with their roots, increasing erosion and water runoff, especially on slopes or near waterways.
Call an Expert
This list highlights the most common Colorado tree pests our experts encounter, but it’s not exhaustive. If you’re ever unsure, contact Front Range Arborists for assistance. The mountain pine beetle is just one pest that can be prevented with treatment. Preemptive care is key to maintaining healthy trees—waiting until an infestation takes hold can be costly and often ineffective. Infestations can result in the loss of multiple trees, a problem that can potentially be avoided.
We specialize in keeping trees healthy through pruning, pest management, fertilizing, and winter watering. We also offer tree and stump removal, as well as fire mitigation services.
Don’t let pests destroy your trees. Regularly inspect them for signs of disease or pest damage and ensure you have preventive treatments in place. If you spot any issues or want to schedule pest prevention, contact us. We proudly serve the greater Colorado Springs area for both residential and commercial tree services.