Swarm Traps: Catching Free Bees With a Box

A honey bee swarm is, temporarily, homeless. The cluster of 10,000 to 30,000 bees hanging from a tree branch or fence post is a colony in transit - they left their parent hive with the old queen, gorged on honey before departure, and now they're waiting. Waiting for the scout bees to find a suitable new home. Waiting for the scouts to argue about it through competitive waggle dances on the cluster surface. Waiting for the democratic process - one of the most thoroughly studied decision-making systems in biology - to converge on a winner.

The scouts are looking for a cavity. And the specifications are remarkably precise.

What the Scouts Want

Thomas Seeley at Cornell University (earlier at Yale) spent decades studying nest-site selection in honey bee swarms, much of it in the Arnot Forest in central New York. His experimental method was elegant: he offered swarms a choice between two or more artificial cavities that differed in a single variable (volume, entrance size, entrance height, entrance direction, cavity condition), and observed which cavity the scouts preferred through dance analysis and occupation tracking.

The results, compiled in his book Honeybee Democracy and numerous papers, describe a bee with surprisingly specific real estate preferences:

Volume: 40 liters. Swarms strongly prefer cavities of approximately 40 liters (about 10 gallons). Cavities smaller than 15 liters are rarely selected. Cavities larger than 100 liters are less preferred than 40-liter cavities. The preference is adaptive: a 40-liter cavity holds enough comb for a full colony's brood nest and winter honey stores without being so large that the colony can't heat it effectively. A deep Langstroth hive body has a volume of approximately 42 liters. The match is coincidental - Lorenzo Langstroth designed his hive based on practical beekeeping experience, not on measurement of wild nest cavities. The bees and the beekeeper arrived at the same number independently.

Entrance size: 10 to 15 square centimeters. Scouts prefer entrances small enough to defend against robbing and predators but large enough for adequate ventilation and traffic flow. An entrance of about 10 to 15 square centimeters - roughly the area of a quarter - is preferred over larger openings. This is why swarm traps with reduced entrances (a 1-inch hole drilled in the face) catch more swarms than traps with wide-open fronts.

Entrance height: 1 to 5 meters above ground. Scouts prefer entrances that are elevated. Cavities at ground level are less attractive than those at 3 to 5 meters (roughly 10 to 15 feet). The preference likely reflects predator avoidance - a nest at ground level is accessible to skunks, raccoons, and bears. In practice, swarm traps mounted 8 to 15 feet high on trees or posts catch more swarms than traps placed at ground level, though even ground-level traps catch some swarms.

Entrance direction: south-facing preferred. In the northern hemisphere, south-facing entrances receive more solar warming in winter and spring. Scouts in Seeley's experiments preferred south-facing entrances over north-facing ones, though the preference was weaker than the preferences for volume and entrance size. The solar exposure advantage is real: a south-facing entrance is warmer on cold mornings, allowing foragers to begin flying earlier in the day.

Previous occupation: strong preference. A cavity that has previously housed a bee colony - one that contains old comb, propolis deposits, and residual pheromones - is dramatically more attractive to scouts than a fresh, clean cavity. The chemical signature of previous bee occupation says "bees lived here and survived." Seeley's experiments showed that cavities rubbed with beeswax and propolis attracted significantly more scouts than identical clean cavities.

This last finding is the single most useful piece of information for anyone setting a swarm trap: old brood comb is the best bait. A frame of dark, used brood comb placed inside a trap is more attractive to scouts than any commercial lure, any essential oil blend, and any amount of lemongrass oil. The chemistry of old comb - a complex mixture of beeswax, propolis, cocoon residue, and residual pheromones - advertises exactly what the scouts are looking for: a proven bee home.

The Decision Process

The swarm's choice of a new home is a democratic process that Seeley has documented in extraordinary detail.

Scouts leave the swarm cluster and search the surrounding area - up to several miles in every direction - for potential cavities. A scout that finds a promising site inspects it thoroughly: entering the cavity, walking the interior walls, measuring the volume (she walks the floor and walls, integrating distance and the optic flow to estimate the enclosed space), checking the entrance, assessing the condition. If the site meets her standards, she returns to the swarm cluster and performs a waggle dance advertising its location and quality.

The vigor of the dance encodes the scout's assessment: a mediocre site gets a short, unenthusiastic dance. An excellent site gets a long, energetic dance that recruits more scouts to visit. The recruited scouts inspect the site independently and, if they agree it's good, return and dance for it as well. If they don't agree, they don't dance, or they dance for a different site.

Multiple scouts may be dancing for different sites simultaneously. The swarm cluster surface becomes a marketplace of competing advertisements. Over hours or days, the dances for superior sites recruit more scouts, while dances for inferior sites fade (scouts naturally stop dancing after a period, and mediocre sites don't recruit enough new scouts to sustain the advertisement). The process converges: eventually, a critical mass of scouts - roughly 15 to 20 - are all dancing for the same site. This quorum triggers the swarm's departure.

The swarm lifts off from the cluster, and the scouts guide 15,000 to 25,000 bees - few of whom have ever visited the chosen site - across distances of up to several kilometers to the new home. The guidance mechanism involves scouts flying rapidly through the airborne swarm in the direction of the new site, then circling back, creating a directional bias in the swarm's movement. The process takes 30 to 60 minutes for a destination within a few kilometers.

The Trap

A swarm trap exploits this natural behavior by providing a cavity that meets the scouts' criteria. The simplest effective swarm trap is a wooden box of approximately 40 liters, with a single entrance hole of 1 to 2 inches diameter, mounted 8 to 15 feet high on a tree or post, baited with old brood comb or a commercial pheromone lure.

The construction materials barely matter. Plywood, solid wood, cardboard, even plastic flower pots have been used successfully. What matters is the volume, the entrance size, the height, and the bait. A crude trap that nails the specifications catches more swarms than a beautiful trap that misses them.

The lure. Commercial swarm lures typically contain synthetic Nasonov pheromone components - citral, geraniol, nerolic acid, and geranic acid - the chemicals that workers release from the Nasonov gland at the tip of their abdomen to signal "this is home." The same pheromone blend that scout bees deposit at a chosen nest site to guide the arriving swarm is what commercial lures attempt to replicate. Lemongrass essential oil contains citral and geraniol in similar ratios to Nasonov pheromone and is used as a low-cost alternative by many swarm trappers.

But the single most effective lure, as Seeley's research confirmed, is an old frame of dark brood comb. The complex chemistry of used comb - hundreds of compounds accumulated over years of brood rearing - broadcasts "bees lived here" more convincingly than any single-compound lure. Trappers who use both comb and a pheromone lure generally catch more swarms than those who use either alone.

The timing. In most of the United States, swarm season runs from mid-April through mid-June, with a peak in May. This is when colonies reach maximum population and the biological drive to reproduce through swarming is strongest. Traps set before swarm season (March) and left through June capture the majority of swarms. A second, smaller swarm season sometimes occurs in late summer (August to September), driven by absconding colonies rather than reproductive swarms.

The location. This is the variable that separates prolific trappers from unlucky ones. Swarm traps near existing apiaries catch more swarms (the swarms are originating from managed colonies nearby). Traps at the edges of open areas - where a tree line meets a field, where a forest opens to a meadow - catch more swarms than traps deep in forest or in the middle of open ground. Scouts search along visual transitions: edges, gaps, clearings. A trap visible from a forest edge is more likely to be found by a scout than one hidden inside dense canopy.

Urban areas, surprisingly, can be excellent for swarm trapping. High densities of managed colonies in urban and suburban areas mean high swarm rates. Urban beekeeping has increased colony density in many cities, and with it, the number of swarms available. A trap on a rooftop, a garage wall, or a fence post in a neighborhood with several backyard beekeepers may catch multiple swarms per season.

The Economics

The economics of swarm trapping are simple: free bees.

A 3-pound package of bees costs $140 to $180 in 2026. A nucleus colony costs $180 to $250. A swarm caught in a trap costs the price of the trap materials - $20 to $50 for a basic plywood box - plus the lure ($5 to $10 for a commercial lure, free for old brood comb). At current prices, a single captured swarm saves $120 to $200 compared to buying a package or nuc.

A trapper running 10 traps - each costing perhaps $30 to build - has invested $300. If 3 of the 10 traps catch swarms (a conservative hit rate in good territory), the captured bees represent $420 to $750 in equivalent purchase value. The return on investment is positive in the first season.

The financial case is even stronger for beekeepers who lose colonies over winter. A beekeeper who winters 10 colonies and loses 4 (a 40 percent loss rate, which is close to the national average) can rebuild through purchased replacements at $600 to $1,000, or through swarm trapping at the cost of materials. The economics are unambiguous.

The non-financial benefits are real too. A swarm of locally adapted bees - bees that have survived the local climate, the local diseases, the local forage conditions - represents genetics adapted to the area. A package of bees shipped from Georgia to Minnesota contains bees bred for Georgia conditions. A swarm caught in Minnesota contains bees whose parent colony survived Minnesota. The local adaptation argument for swarm trapping is the same argument that underlies feral bee conservation and survivor stock breeding programs.

The Catch

Swarm trapping isn't without complications.

Disease risk. A trapped swarm may carry Varroa mites, Nosema, or viral infections from its parent colony. The new colony needs to be monitored and treated just like any other colony. The "free bees" aren't free of pathogens - they're free of purchase cost.

Africanized genetics. In the southern United States - Texas, Arizona, New Mexico, southern California, and Florida - wild swarms may carry Africanized genetics. These colonies are more defensive, more prone to absconding, and more difficult to manage than European-lineage colonies. Trappers in Africanized zones take an additional risk with every trap.

Queen quality. A swarm's queen is the old queen from the parent colony - she left with the swarm, while the new queen stays in the parent hive. This queen is at least a year old, possibly two or three years old, and she's already been superseded once (the colony swarmed because it was strong enough to reproduce, but the queen is the older model). The colony may supersede her within weeks or months of being hived. This is natural and expected - the colony is replacing an aging queen with a fresh one mated to local drones.

Legal issues. In some jurisdictions, beekeeping regulations require registration of colonies, and colonies obtained through swarm trapping are not exempt. Some HOAs and municipal codes restrict the placement of swarm traps. The legal landscape varies by location.

The Feral Connection

Swarm trapping intersects with the broader question of feral honey bee populations in the United States. Before Varroa mites arrived in the late 1980s, feral honey bee colonies were abundant throughout the country - inhabiting hollow trees, building walls, attics, and any other cavity that met their specifications. The Varroa invasion killed an estimated 90 percent of feral colonies in North America.

The feral population has partially recovered, particularly in areas where Varroa-resistant genetics have developed through natural selection. Seeley's work in the Arnot Forest documented a population of feral colonies that survived Varroa without treatment by evolving smaller colony sizes, higher swarming rates, and behavioral resistance mechanisms.

Swarm traps catch both managed-colony swarms and feral-colony swarms. In areas with established feral populations, a significant fraction of trapped swarms may originate from unmanaged colonies - bees that have survived without human intervention, whose genetics have been selected by the environment rather than by a breeder. These feral genetics are valued by beekeepers interested in treatment-free or low-treatment management, because the bees have already demonstrated survival capability.

The trap, in this context, is a sampling tool for the local gene pool. It catches whatever the local bee population is producing, filtered through the democratic decision-making of the swarm's scouts. The bees that arrive in the trap represent the genetic output of every colony within foraging range - managed and feral, treated and untreated, purchased and wild-caught.

The Oldest Trick

Catching swarms in bait containers is probably as old as beekeeping itself. The ancient practice of setting out clay pots or hollow logs to attract wild swarms - documented in Egyptian, Greek, and Ethiopian traditions - is swarm trapping by another name. The modern plywood box with a drilled entrance is the technological descendant of the empty clay amphora placed on a rooftop in ancient Crete.

The bees haven't changed their house-hunting criteria in millions of years. The 40-liter cavity, the small entrance, the elevated position, the scent of previous occupation - these preferences were shaped by millions of years of natural selection in which the colonies that chose good cavities survived and the colonies that chose bad ones didn't. The scout bees evaluating a swarm trap in a suburban backyard in 2026 are running the same assessment algorithm that their ancestors ran when evaluating hollow trees in the Miocene.

The trap works because the builder knows what the scouts want. And the builder knows what the scouts want because Thomas Seeley spent 30 years asking them. He offered choices. He tracked dances. He counted scouts. He measured volumes. He published the specifications.

A 40-liter box. A 1-inch entrance hole. 10 to 15 feet off the ground. A frame of old brood comb inside. Set it out in April. Wait. The scouts will find it. They'll inspect it. If it meets their standards - and the specifications are designed to meet their standards - they'll dance for it. The swarm will arrive. 15,000 bees, a queen, and 60 grams of honey in their crops, moving into a box that cost $30 to build and caught $200 worth of bees.

The oldest trick in beekeeping is still the best deal.