Trees are fundamental components of ecosystems, converting sunlight into energy and providing food and habitat for diverse organisms. The concept of something “eating” a tree includes consuming leaves, boring into wood, extracting sap, or breaking down tissues, as with fungi.
Insects That Damage Trees
Insects often damage trees through diverse feeding habits, targeting different parts and impacting health. Their methods vary widely depending on the species and the tree part affected.
Wood-Boring Insects
Wood-boring insects tunnel into a tree’s wood, bark, and cambium, disrupting its vascular system and weakening its structure. Evidence includes D-shaped exit holes, frass, and galleries beneath the bark.
Emerald ash borers create D-shaped exit holes as adults emerge, and their larvae tunnel extensively under the bark, ultimately girdling and killing ash trees.
Bark beetles, such as the Ips beetle and mountain pine beetle, bore into the bark and cambium, introducing fungi that further impede the tree’s ability to move water.
Asian longhorned beetles leave distinct round exit holes, and their larvae tunnel deep into the heartwood, weakening branches and trunks.
Carpenterworms also tunnel into wood, creating large, irregular galleries that can severely compromise a tree’s structural integrity.
Defoliating Insects
Defoliating insects consume tree leaves or needles, directly impacting photosynthesis. Severe defoliation weakens trees, reduces growth, and increases susceptibility to stressors or diseases.
Gypsy moth caterpillars are known for their voracious appetite, capable of stripping entire forests of their leaves during outbreaks.
Tent caterpillars construct silken nests in tree branches and feed on foliage, often leading to noticeable defoliation.
Fall webworms create large, unsightly silken webs around branches, within which their larvae feed on leaves.
Sawfly larvae and various leaf beetles chew through leaf tissue, sometimes leaving only the veins in a pattern known as skeletonization, further reducing the tree’s photosynthetic capacity.
Sap-Sucking Insects
Sap-sucking insects pierce plant cells to extract sap, leading to tree weakening, deformities, and disease transmission. Their presence often results in visible symptoms.
Aphids, small, soft-bodied insects, cluster on new growth and undersides of leaves, extracting sap and often excreting honeydew, which can lead to sooty mold growth.
Scale insects, which appear as small bumps on stems and leaves, also feed on sap, causing yellowing leaves and stunted growth.
Mealybugs are another group of soft-bodied insects that create cottony masses as they feed on sap.
Leafhoppers can cause stippling and curling of leaves.
Cicada nymphs feed on sap from tree roots for extended periods, potentially impacting tree vigor over time.
Mammals That Damage Trees
Mammals can cause considerable tree damage through feeding or territorial behaviors, ranging from minor issues to significant structural harm, especially for younger trees. This impact can significantly affect tree health and survival.
Grazing and Browsing Animals
Grazing and browsing animals consume foliage, twigs, and young bark, stunting growth, deforming shape, and reducing vitality, especially in saplings. This damage is common where wildlife populations are abundant.
Deer are frequent browsers, eating tender twigs and leaves, especially on young trees.
Male deer also rub their antlers against tree trunks to remove velvet or mark territory, which can strip bark and expose inner tissues, typically affecting trees around four inches in diameter.
Rabbits often gnaw on the bark of young trees and clip off small stems, particularly during winter months when other food sources are scarce.
Voles, small rodents, commonly chew on the bark at the base of trees, often hidden under snow cover, which can girdle the tree and disrupt nutrient flow.
Gnawing Animals
Gnawing animals use their teeth to remove bark or fell trees. Girdling, the removal of a complete bark and cambium ring, interrupts nutrient and water flow, often killing the tree.
Beavers are well-known for their ability to fell trees using their powerful incisors, primarily for dam construction and as a food source, as they consume the inner bark and tender branches. Porcupines gnaw on bark, often targeting upper branches, which can lead to branch dieback and weaken the tree’s structure. Squirrels, while primarily consuming nuts and seeds, will sometimes gnaw on tree bark, buds, and even young branches, particularly during periods of food scarcity, or to access sap.
Fungi and Pathogens That Damage Trees
Fungi and other pathogens decompose tree tissues, causing rot, disease, and structural failure. While important decomposers, their activity on living trees can be detrimental.
Wood-decay fungi break down lignin and cellulose. Heart rot, an internal wood decay, often manifests as conks on the trunk, indicating core decay. Root rot fungi attack the root system, causing instability, reduced nutrient uptake, and tree decline.
Other pathogens, including fungi and bacteria, cause cankers and blights. Cankers are localized dead tissue on branches or trunks. Blights are rapid, widespread killing of plant tissues. These infections weaken tree structure, reduce lifespan, and can lead to demise.