Bark Beetle: Identification, Damage & How to Get Rid of Them

What Is a Bark Beetle?

Bark beetles are small, cylindrical insects belonging to the family Curculionidae (weevils), subfamily Scolytinae. These native forest insects bore into tree bark to lay eggs, with larvae feeding on the nutrient-rich phloem layer just beneath the bark surface. While bark beetles play a natural role in forest ecosystems by attacking weak trees, population explosions can devastate vast forest areas.

Species Overview

Several bark beetle species cause significant damage in North America:

Where Bark Beetles Are Found

Bark beetles are found throughout North American forests, from the boreal forests of Canada to the pine forests of the southeastern United States. The most severe outbreaks occur in the Rocky Mountain region, Pacific Northwest, and Sierra Nevada mountains. Climate change has expanded their range northward and to higher elevations, with warmer winters allowing populations to survive in previously inhospitable areas.

In Colorado alone, spruce beetles have affected 1.84 million cumulative acres from 1996-2018, with approximately 40% of the state's spruce-fir forest ecosystems impacted. Mountain pine beetles have killed trees across millions of acres from British Columbia through Colorado.

How to Identify Bark Beetles

Size, Color, and Appearance

Adult bark beetles are small, cylindrical insects typically measuring 3-7mm (1/8 to 1/4 inch) in length. Most species are dark brown to black, though some appear reddish-brown. Key identifying features include:

• Body shape: Cylindrical, bullet-shaped with a rounded rear end
• Antennae: Elbowed with a club-shaped tip
• Head: Partially hidden beneath the thorax when viewed from above
• Elytra (wing covers): Often with rows of small pits or ridges

Signs of Bark Beetle Infestation

Early detection is critical for protecting trees. Watch for these warning signs:

What Damage Do Bark Beetles Cause?

Damage to Trees

Bark beetles kill trees through a combination of physical damage and biological warfare. As adults bore into the bark, they introduce blue stain fungi (Ophiostoma species) that colonize the sapwood and block the tree's water-conducting tissues. Meanwhile, larvae feed on the phloem layer, disrupting nutrient transport. This two-pronged attack typically kills trees within weeks to months.

Signs of Infested Wood

Infested wood displays several characteristic signs:

• Entry and exit holes (1-3mm diameter) scattered across bark surface
• Winding gallery patterns visible when bark is removed
• Blue-gray staining in sapwood visible in cross-sections
• Loose, easily peeling bark on dead or dying trees
• White larvae or pupae in galleries (seasonal)

How Fast They Spread

Bark beetle spread varies dramatically based on population levels and environmental conditions. During endemic (low population) periods, beetles primarily attack weakened or stressed trees. However, during epidemic outbreaks, populations can explode exponentially:

Why Bark Beetles Attack Trees

Weak or Stressed Trees

Bark beetles preferentially attack trees that are already compromised. Stressed trees produce fewer defensive compounds (terpenes and resin) and cannot effectively "pitch out" invading beetles. Trees become stressed from:

• Drought: Reduces resin production and overall tree vigor
• Root damage: Construction, compaction, or disease
• Competition: Overcrowded stands compete for water and nutrients
• Other pests: Defoliators, diseases, or previous beetle attacks
• Age: Older, mature trees are more susceptible than young, vigorous trees

Environmental Factors

Climate change has dramatically increased bark beetle populations and expanded their range. Key environmental factors include:

How to Get Rid of Bark Beetles

Removing Infested Wood

The most effective control for active infestations is removing and destroying infested wood before beetles emerge to attack new trees. Timing is critical—beetles must be destroyed while still inside the wood:

• Fall/Winter removal: Fell infested trees after beetle flight season ends and before spring emergence
• Solar treatment: Cut logs, stack in full sun, and cover with clear plastic to heat-kill beetles
• Debarking: Remove bark from cut logs to destroy larvae and pupae
• Chipping: Process infested wood into chips, which dry too quickly for beetle survival
• Burning: Where permitted, burning infested slash destroys all life stages

Chemical Treatments

Chemical treatments are preventive only—they cannot save trees already infested. Insecticides create a barrier that kills beetles before they can bore into the bark. Treatment must be applied before beetle flight season begins:

Natural Control Methods

Several natural and low-chemical approaches can help manage bark beetle populations:

• Trap trees: Fell trees to attract beetles, then destroy before emergence
• Pheromone packets (MCH): Methylcyclohexanone disrupts beetle aggregation on treated trees
• Verbenone: Anti-aggregation pheromone signals "tree is full" to incoming beetles
• Forest thinning: Reduces competition and increases tree vigor to resist attacks

Best Treatments for Bark Beetles

Insecticide Sprays

Pyrethroid insecticides are the primary preventive treatments for bark beetles. The Colorado State Forest Service recommends spraying only high-value trees near homes, businesses, or recreation sites:

Preventive Tree Treatments

Beyond insecticides, several preventive treatments can protect trees:

• MCH packets: Hang Methylcyclohexanone packets on spruce trees to deter spruce beetles
• Verbenone pouches: Anti-aggregation pheromone pouches for mountain pine beetle
• Systemic injections: Emamectin benzoate injections provide 2-3 year protection

Professional Pest Control

For large trees or severe infestations, professional arborists and pest control operators offer specialized services:

• High-pressure bark sprays reaching the full trunk height
• Tree injections for systemic protection
• Safe removal of large infested trees
• Forest-wide management planning for large properties

How to Prevent Bark Beetle Infestation

Tree Care and Maintenance

The most effective long-term defense against bark beetles is maintaining healthy, vigorous trees that can defend themselves:

Monitoring and Early Detection

Regular monitoring allows early intervention before infestations spread:

• Inspect trees monthly from May through October for pitch tubes and boring dust
• Watch for fading or discoloring needles in the crown
• Note increased woodpecker activity on trunks
• Check state forest service maps for outbreak areas near your property
• Contact a certified arborist if you suspect infestation

Are Bark Beetles Dangerous to Homes?

Bark beetles do not infest structural wood in homes. They require living or freshly cut wood with moisture and phloem (the nutrient-conducting layer beneath bark) to survive. Dried, processed lumber in homes is not suitable habitat.

However, bark beetles pose indirect risks to homes:

• Falling hazards: Dead trees near structures can fall, especially during storms or snow loading
• Fire risk: Masses of dead trees dramatically increase wildfire fuel loads
• Property values: Large-scale tree mortality can reduce property values
• Firewood storage: Storing infested firewood can spread beetles to nearby healthy trees

FAQs About Bark Beetles

Final Tips to Protect Trees from Bark Beetles

Protecting your trees from bark beetles requires a proactive, integrated approach. Here are the key takeaways: