What Bees Make Nests in Trees? A Field Look

Dozens of bee species nest in trees, and honey bees are just the most familiar example. Carpenter bees bore tunnels directly into wood, stingless bees overwhelmingly choose cavities in living trunks, and leafcutter bees line hollow stems and rotting logs with discs of leaf. Even some mason bees and resin bees depend on tree-associated cavities for reproduction. The variety is far wider than most people expect, and the relationship between bees and trees runs deeper than simple shelter.

Honey Bees in Tree Cavities

Western honey bees are probably the first species that come to mind when you picture a bee nest in a tree. Feral and wild honey bee colonies seek out enclosed spaces with small, defensible entrances, and a hollow in a mature tree trunk fits the bill perfectly. A suitable cavity needs to be large enough to support comb-building and food storage, yet enclosed enough to maintain stable interior conditions. Old-growth forests and woodlands with large, aging trees tend to have the most natural cavities available. Managed landscapes with younger trees, on the other hand, rarely offer the right kind of hollows, which is one reason feral colonies in urban and suburban areas end up in wall voids and chimneys instead.

Once a colony moves in, it actively manages the cavity’s temperature. A case study from Białowieża Primeval Forest in Poland measured what happens inside a tree hollow after honey bees colonize it. The occupied cavity was warmer than an unoccupied control cavity around the clock, but the effect was strongest at night, when worker bees ramped up heat production by roughly 7 °C above what the empty hollow would have been. During daylight hours, the difference shrank to about 2–3 °C as the colony dialed back its metabolic heating and possibly increased ventilation. The result is a buffered interior climate that stays more stable than the forest air outside, protecting brood and stored honey from temperature swings.¹

Stingless Bees and Their Devotion to Living Trees

If honey bees are the poster species for tree-cavity nesting, stingless bees are the true specialists. These small, tropical and subtropical bees (tribe Meliponini) show an almost exclusive preference for living tree trunks. A study in Brazil found that about 85% of stingless bee nests were located in cavities of living trees, with dead trees, dry trunks, and termite mounds making up the remainder.² Fieldwork in Sabah, Malaysia, reported a similar pattern: over 90% of stingless bee nests were closely associated with living trees, either inside pre-formed trunk cavities or situated in or under the tree base.³

That preference for living trees is not accidental. Living trees offer structural stability, and their cavities tend to persist for years or decades, which matters because stingless bee colonies are perennial. A dead trunk eventually collapses, but a living one can house the same colony across multiple generations. Stingless bees also make heavy use of tree resin, collecting it to build nest structures, seal cracks, and repel predators. Some species even smear resin on invaders to immobilize them. Research on resin use suggests that resin-derived compounds become part of the bees’ own body chemistry and help shape the microbial community inside the nest.⁴

This tight dependence on large living trees has practical consequences for conservation. When mature tropical trees are removed through logging or land clearing, stingless bees lose not just their food sources but their nesting habitat. In urban environments, some stingless bee species have shown flexibility, colonizing man-made substrates like concrete walls and drainage pipes when natural tree hollows are scarce. One study of Asian stingless bee communities in cities found that over half of all recorded nests were in man-made substrates, though large trees in green spaces still supported the most nests.⁵

Large Carpenter Bees

Carpenter bees in the genus Xylocopa take a fundamentally different approach to tree nesting. Rather than moving into a pre-existing hollow, they create their own. Using powerful mandibles, female carpenter bees chew tunnels into dead wood, weathered limbs, and exposed heartwood. They don’t eat the wood; they excavate it, producing telltale piles of sawdust below the entrance hole. Each tunnel typically branches into several chambers where individual eggs are provisioned with a ball of pollen and sealed off with a partition of chewed wood pulp.

Not all carpenter bees target trees. Many species in temperate regions are infamous for drilling into unpainted deck boards, fence rails, and fascia trim on houses. But in forested habitats, standing dead trees and fallen logs are their natural substrate. Studies of tropical Xylocopa species in Costa Rica have documented nests in various natural wood substrates, and the bees show preferences for particular hardness levels and states of decay.⁶

Carpenter bees are among the largest bees in the world, with some tropical species exceeding 2.5 cm in body length. Phylogenetic work on the carpenter bee subfamily Xylocopinae has traced the evolutionary history of these wood-nesting bees, showing that the most recent common ancestor of the group was solitary. Social behavior has evolved independently multiple times within the lineage, though most species remain solitary or only loosely social.⁷

Small Carpenter Bees in Pithy Stems

The small carpenter bees of the genus Ceratina are the miniature cousins of Xylocopa, but their nesting habits differ in an important way. Instead of boring into solid wood, Ceratina species exploit the soft pith inside broken or cut plant stems. Classic observations from the early twentieth century describe how the small carpenter bee Ceratina calcarata burrows only into the exposed soft pith of elder or sumac stems. If the soft core is not exposed by a break or cut, the bee cannot chew through the tough outer wall and has to find another stem.⁸

This habit means Ceratina bees are often found nesting in the branches or twigs of trees and shrubs, but only after something has snapped or pruned the stem open. Gardeners who leave dead raspberry canes, elderberry stalks, or other pithy stems standing through winter are inadvertently providing nest sites for these tiny bees. The nests are linear, with a series of small cells stacked inside the hollow pith channel, each provisioned with pollen and sealed with a pith plug.

Leafcutter Bees and Mason Bees

Leafcutter bees in the genus Megachile are among the most widespread cavity nesters, and many species make extensive use of tree-associated sites. These bees cut neat, circular or oval pieces from leaves using their mandibles, then carry the leaf fragments back to a pre-existing cavity where they press them into place to form lined brood cells. The cavities they use include hollow plant stems, beetle exit holes in dead wood, and sometimes crevices in tree bark.⁹ Some species have been documented nesting directly in the trunks of old pistachio trees, preferring pre-existing cavities in aging wood.¹⁰

What makes leafcutter bees distinctive is their double relationship with plants: they visit flowers for pollen and nectar like other bees, but they also physically harvest leaf tissue as a building material.¹¹ If you’ve ever noticed semicircular notches cut from the edges of rose, birch, or lilac leaves, a Megachile bee is the likely culprit.

Mason bees (genus Osmia and relatives) overlap with leafcutter bees in their use of pre-existing cavities, including abandoned beetle galleries in dead wood and holes in tree bark. Most bee species worldwide nest in the soil, but mason bees are among the minority that nest in wooden cavities above ground.¹² Rather than lining their cells with leaf pieces, mason bees use mud, chewed plant material, or a mix of both to build partitions between brood cells. They are generalist pollinators prized for orchard work, and their willingness to use drilled wooden blocks and bundled paper tubes has made them popular subjects for backyard “bee hotels.”

Resin Bees and What They Borrow From Trees

Resin bees are a loose grouping of solitary species (spanning several genera) that collect plant resins and use them as a primary construction material in their nests. The resins typically come from conifers, tropical hardwoods, and flowering trees that produce sticky exudates as part of their own defense against insects and fungi. The bees repurpose this material for structural support, waterproofing, and antimicrobial protection inside the nest. Research on functional resin use in solitary bees has grouped these roles into several categories: nest structure, chemical camouflage, defense against parasites, moisture regulation, and suppression of microbial growth.¹³

Some resin bees nest in tree cavities themselves; others use ground holes or crevices in rock but still depend on nearby trees for their resin supply. The dependence on resin creates an indirect but real link between these bees and the health of local tree populations: if the resin-producing trees disappear, the bees lose a critical nesting resource even if their physical nest site is elsewhere.

Where in the Tree Do Bees Nest?

When people imagine a bee nest in a tree, they tend to picture a cavity partway up the trunk. That is accurate for honey bees and many stingless bees, but the full picture involves every vertical layer of a forest. Research on spring bee communities in temperate forest edges found that female solitary bees, social bees, and both soil-nesting and wood-nesting species were abundant in the canopy, while ground-nesting and solitary bees of both sexes dominated the understory layer closer to the forest floor.¹⁴ In other words, tree-nesting bees are not confined to trunks; they use broken canopy branches, exposed limbs, and high cavities that are easy to miss from the ground.

This vertical spread matters for anyone trying to survey or conserve tree-nesting bees. Ground-level inspections undercount the species that nest high in the canopy. It also helps explain why tree-nesting bees may be more common than field estimates suggest: many nests are simply invisible from below.

Why Standing Dead Wood Is So Valuable

The link between bees and trees is not limited to living trunks. Standing deadwood, whether left by natural mortality, storm damage, or selective forestry, provides a different but equally important nesting resource. Dead trees develop cracks, peeling bark, and beetle galleries that cavity-nesting bees exploit. A forest restoration experiment found that plots enriched with structural complexity had higher estimated bee species richness than control plots, and that deadwood from restoration efforts specifically increased the number of aboveground-nesting, solitary, and cuckoo bee individuals. Standing deadwood had a particularly strong positive effect.¹⁵

Separate work examining how forest structure affects bees and wasps confirmed that standing deadwood, along with canopy cover and overall structural complexity, was principally important for the abundance, diversity, and species richness of forest specialist bees.¹⁶ The practical takeaway is straightforward: leaving dead trees standing in managed forests, parks, and even backyards supports far more nesting bees than a tidy landscape with all deadwood removed.

Heat Tolerance and the Cost of a Hot Nest

The type of nest a bee builds or occupies shapes more than just its reproductive success. It also influences the species’ tolerance to heat, which has consequences under a warming climate. A large-scale study comparing heat tolerance across many bee species found that bees nesting in stems were, on average, the most heat tolerant, while ground-nesting bees were the least. The explanation is that stems and above-ground wood cavities experience higher and more variable temperatures than underground burrows, so stem-nesting lineages have been under stronger selection to withstand heat. Ground-nesting bees, buffered by the cooler, more stable soil environment, have not faced the same pressure.¹⁷

This creates a paradox for conservation. Ground-nesting bees, which make up the majority of bee species worldwide, are physiologically the least prepared for rising temperatures. Tree- and stem-nesting bees may be inherently more resilient because their nesting habit has already pushed them toward heat tolerance. But that does not mean tree-nesting bees are safe from climate change; losing the trees they depend on for shelter eliminates their advantage.

Uninvited Guests at the Tree Cavity

A tree cavity full of honey, wax, and brood is an attractive target for animals other than bees. Camera-trap monitoring of honey bee colonies nesting in black woodpecker cavities in German forests revealed a busy parade of visitors: at least 13 bird species and two mammal species were recorded approaching occupied nest trees during a single winter. In about 41% of the camera captures, visitors pushed at least part of their body into the cavity, suggesting they were raiding or attempting to raid the colony’s stores.¹⁸

For solitary tree-nesting bees, the threats are different but no less real. Cuckoo bees (also called kleptoparasitic bees) sneak into unattended nests and lay their own eggs, which hatch and consume the provisions meant for the host’s offspring. Parasitic wasps and flies target leafcutter and mason bee nests as well. The choice of nest site, including factors like entrance size and cavity depth, is partly an evolutionary response to this constant pressure from nest parasites and predators.

Helping Tree-Nesting Bees in Your Own Landscape

You do not need a forest to support tree-nesting bees. A few deliberate choices in a yard or garden can make a measurable difference. Leaving broken stems and dead branches in place rather than pruning them away offers small carpenter bees and leafcutter bees the substrate they need. A standing dead trunk, if it does not pose a safety risk, can serve the same purpose as a snag in a national forest. For those who want a more structured approach, artificial trap nests made from bundles of hollow reeds or drilled wooden blocks mimic the cavities that mason bees and leafcutter bees seek out. Community science projects across Canada have used exactly this kind of trap nest to monitor cavity-nesting bee and wasp distributions, demonstrating that even school grounds and suburban yards attract a range of species when nesting sites are available.¹⁹

A few things to keep in mind if you set up a bee hotel or leave natural nesting features in place. Drill holes between about 6 and 10 mm in diameter for mason bees and leafcutter bees; anything much larger or smaller will attract different occupants or none at all. Place the structure facing morning sun in a sheltered spot. Clean or replace tubes annually to reduce the buildup of parasites and mold. And resist the urge to seal or paint over beetle holes in old fence posts or firewood stacks. Those holes are prime real estate for solitary bees that spend their whole lives within a few hundred meters of where they hatched.