Animals interact with wood for various reasons, from maintaining physical health to constructing their environment. The motivation defines the difference between animals that simply gnaw on wood and those that actively consume it. Gnawing is often required for survival, such as regulating continuous physical growth or shaping materials into a functional habitat. Other species consume wood to extract nutrition or excavate it solely to create shelter. Understanding these behaviors reveals the distinct biological needs and ecological roles of wood-interacting species.
Gnawing Mammals: Chewing for Dental Health
A large group of mammals, belonging to the order Rodentia, gnaws on wood not for nutrition but out of biological necessity to control the length of their teeth. All rodents, including mice, squirrels, rats, porcupines, and voles, possess a single pair of upper and lower incisors that grow continuously throughout their lives. This unique dental structure prevents the teeth from being worn down completely by their abrasive diet of seeds, nuts, and tough plant matter.
The incisors are constructed with a hard enamel layer on the front and a softer dentine layer on the back. As the rodent gnaws, the softer dentine wears away faster than the enamel, maintaining a perpetually sharp, chisel-like edge. If a rodent cannot gnaw on sufficiently hard material, the incisors will overgrow, eventually curving into the jaw or mouth and preventing the animal from eating.
Rodents will gnaw on a wide variety of materials, including wood, plastic, metal, and electrical wiring. In a natural environment, this behavior involves stripping bark from trees or boring shallow scrapes into wood, distinct from the structural tunneling seen in insects. The damage is characterized by parallel teeth marks left on the surface, a byproduct of the constant need to shorten and sharpen their specialized incisors.
Wood-Consuming Insects: Food and Nesting
Invertebrates, primarily insects, interact with wood either as a food source or as a protective medium for nesting. Termites are true consumers of wood, extracting nutritional value from the tough cellulose material. These insects possess specialized gut protozoa or bacteria that produce the enzymes necessary to break down cellulose into digestible sugars. A mature colony of subterranean termites can consume nearly five grams of wood daily, causing extensive internal damage.
Other insects, such as carpenter ants and carpenter bees, do not consume the wood they chew but excavate it to create chambers for shelter and reproduction. Carpenter ants bore into wood, often selecting moist or decaying material, to create smooth, clean galleries for their nests. They discard a fine sawdust-like debris called frass, which they push out of small holes. Similarly, female carpenter bees chew into softwoods to create perfectly round entrance holes leading to tunnels that run parallel to the wood grain. They line these excavated tunnels with pollen and nectar to feed their young.
Specialized Builders: Wood Use for Habitat Construction
A few species, most famously the beaver, utilize wood primarily as an engineering material to construct complex habitats. North American and Eurasian beaver species are known as ecosystem engineers for their ability to fell trees and use the material to build massive dams and lodges. The dam’s purpose is to create a pond of deep, still water, which provides a safe, submerged entrance to their lodge and allows them to float heavy branches to the construction site.
Beavers use their powerful incisors to cut down trees, gnawing a characteristic hourglass shape around the trunk until it falls. They chew the felled tree into manageable sections, which they drag or float into position for the dam or lodge. Construction involves weaving together logs and branches, then sealing the structure with mud, rocks, and smaller debris to make it watertight and secure. While they do not eat the structural wood, they consume the nutritious inner bark and tender twigs from the branches they harvest, combining habitat construction and food procurement.