While many people associate bees with artificial hives or ground nests, a variety of bee species naturally utilize trees for their nesting sites. These arboreal homes offer unique advantages, providing shelter and stability for different bee life cycles. Understanding which bees choose trees and why helps appreciate their diverse nesting behaviors in nature.
Types of Bees That Nest in Trees
Honey bees, social insects living in large colonies, commonly establish their nests within hollow trees or other natural tree cavities. These spaces provide the necessary protection for their wax combs, which house their brood and store honey. When a honey bee colony outgrows its current space, a portion of the colony, known as a swarm, will temporarily cluster on a tree branch while scout bees search for a new, permanent tree cavity or similar enclosed space.
Carpenter bees, named for their wood-boring habits, are another type of bee that nests in trees, specifically by tunneling into wood. Unlike honey bees, carpenter bees are largely solitary, with a female constructing her own nest. They prefer untreated or weathered softwoods like cedar or pine, creating perfectly round entry holes, typically about 3/8 to 1/2 inch in diameter, that lead to extensive tunnels within the wood.
Many solitary bees, such as mason bees and leafcutter bees, also utilize trees for nesting, though their methods differ. These bees do not bore into healthy wood but instead occupy existing tunnels or cavities. Leafcutter bees, for example, use natural tree cavities or hollow stems, lining their individual brood cells with meticulously cut pieces of leaves or flower petals. Mason bees, on the other hand, use mud or other materials to partition their nesting tubes within pre-existing holes. While bumble bees primarily nest underground in abandoned rodent burrows, some species, like the tree bumblebee, will opportunistically nest in above-ground cavities such as bird boxes or tree holes.
Why Bees Choose Trees for Nests
Trees offer bees a secure and stable environment for raising their young and storing resources. The natural cavities found in trees provide excellent insulation, helping to regulate temperature within the nest, protecting the colony from extreme heat and cold. This thermal stability is beneficial for the development of larvae and the survival of the colony through different seasons. The elevated location and enclosed nature of tree cavities also offer protection from various predators that might otherwise disturb ground-level nests. A small, defensible entrance, often facing away from prevailing winds, further enhances the security of the nest.
How to Identify Tree Nests
Identifying bee nests in trees involves observing both the nest structure and the behavior of the bees around it.
Honey bee nests are typically found inside hollows or cavities within the tree trunk or large branches. If visible, their comb will have a distinctive hexagonal wax cell pattern, and the entrance hole is often small, with bees actively flying in and out. A humming sound coming from within the tree can also indicate a honey bee colony.
Carpenter bee activity is identified by perfectly round entry holes, approximately 3/8 to 1/2 inch in diameter, often found on the underside of wooden structures or tree limbs. Piles of sawdust-like material, called frass, may accumulate directly below these holes, along with yellowish or brownish excrement stains. Solitary bees like mason and leafcutter bees utilize pre-existing holes, often with individual cells capped with mud or leaf pieces visible at the entrance.
Distinguishing bee nests from those of wasps or hornets is important. Honey bees and bumble bees have fuzzy bodies, while wasps and hornets generally have smoother, more slender bodies and a more defined “waist.” Wasp and hornet nests are often constructed from chewed wood pulp, giving them a papery appearance. Unlike many wasps, bees do not typically build exposed paper nests hanging from tree branches.
Living Alongside Tree-Nesting Bees
It is generally advisable to coexist with tree-nesting bees when possible. Most bee species are not aggressive unless their nest is directly threatened or disturbed. Bees are important pollinators, contributing to plant reproduction and ecosystem health. Observing nests from a distance is recommended to avoid disturbing the bees.
If a honey bee colony is established in an inconvenient or problematic location, contacting a local beekeeper is often the best course of action. Beekeepers may be able to safely remove and relocate honey bee swarms or established colonies without harming them. For other bee types, particularly solitary species, their presence is usually harmless to humans and the tree itself, as they do not typically cause structural damage. Conservation efforts that preserve natural tree cavities support these important pollinators.