Carpenter bees typically go away in mid to late fall, once cold temperatures and dwindling flowers trigger hibernation. They don’t leave entirely, though. The adults retreat into wood tunnels and stay hidden through winter, then re-emerge in April or May to start the cycle over. So while they disappear from sight for roughly five to six months, they’re often still inside the very structures they drilled into.
The Full Activity Timeline
Carpenter bees follow a predictable yearly pattern with one generation per year. Adults emerge from their tunnels in April or May and immediately begin mating and drilling new nests or expanding old ones. This is the period when most people notice them: large, black, bumble-bee-sized insects hovering around decks, eaves, and fascia boards. Males will aggressively hover near you but can’t sting. Females can sting but rarely do.
Nest construction and egg-laying continue through late spring into early summer. By the end of July, females have stocked each brood chamber with a ball of pollen and nectar and sealed it off with a partition made from chewed wood particles. The larvae feed on those provisions inside the tunnel through mid-summer, then mature into adults and emerge in August.
These newly emerged adults begin foraging within a week or two and stay active through fall. Once temperatures drop and flowers become scarce, they settle into existing tunnels to hibernate for winter. In northern states like Pennsylvania, that hibernation starts around October or November. In warmer southern regions, carpenter bees can remain active into November or even December, and they may emerge earlier in spring, sometimes as early as March.
Where They Go in Winter
Carpenter bees don’t migrate or die off when cold weather arrives. Multiple adults overwinter together inside the same tunnels they or previous generations drilled. They enter a dormant state and survive on stored body fat until spring warmth brings them back out. This is why the same holes in your deck or pergola attract bees year after year. The tunnels are permanent housing, not seasonal structures.
Fall-emerged adults sometimes enlarge existing holes or create entirely new ones before settling in for winter. So even after visible activity stops, new damage to wood can appear in early fall as bees prepare their hibernation quarters.
Peak Nuisance Periods
You’ll notice carpenter bees most during two windows. The first and most intense is late April through June, when adults are drilling fresh tunnels, mating, and hovering territorially around wooden structures. The buzzing, the sawdust piles beneath round half-inch holes, the dive-bombing males: that’s all concentrated in this spring window.
The second, quieter wave comes in August and September when the new generation emerges and forages. These bees are less focused on drilling and more focused on feeding, so they’re less of a structural concern. But you’ll still see them around flowers and occasionally near wood surfaces.
Best Time to Address the Damage
If carpenter bees are damaging your home, timing matters more than most people realize. Treating active nests in late spring or summer is largely ineffective because each brood chamber is sealed behind wood-particle partitions that block anything you apply from reaching the developing larvae inside.
The two effective treatment windows are:
- Early spring (March to mid-April), before nesting activity begins, when overwintering adults are still inside the tunnels
- Early fall (September to October), after all new adults have emerged and are settling into tunnels for hibernation
In either window, the goal is to apply a dust insecticide (boric acid or diatomaceous earth work well) into the tunnel opening, then leave the hole open for a few days so returning bees contact the treatment. After that waiting period, seal the holes with caulking, a short wooden dowel, or wood putty, then repaint the surface. The paint or finish is important: carpenter bees strongly prefer bare, untreated wood and are far less likely to drill into painted or stained surfaces.
Why They Keep Coming Back
Carpenter bees reuse and expand tunnels year after year. A single tunnel can grow to ten inches or longer over multiple seasons, and branching galleries can cause real structural damage over time, especially in railings, window trim, and deck joists. If you seal holes without treating them first, overwintering bees trapped inside will simply drill a new exit. And if you leave old tunnels open, the next spring’s generation will find them and move right in.
The most reliable long-term prevention is finishing any exposed wood surfaces with paint, stain, or varnish. Carpenter bees are native pollinators that play a genuine role in your garden’s ecosystem, so if the damage is cosmetic and limited to a fence post or garden structure, leaving them alone is a reasonable option. But for load-bearing wood or repeated infestations in the same spot, sealing and finishing the wood after a fall or early spring treatment breaks the cycle.