Bee Swarm on Your House or Tree: What It Means and Who to Call
A bee swarm is a honey bee colony reproducing: the old queen and about half to two-thirds of the workers leave their hive and hang in a cluster on a branch, fence or wall while scouts search for a new home. Swarming bees are usually gentle, most clusters move on within an hour to a day or two, and the right call is a local beekeeper, not a can of spray. The exception is bees flying in and out of a gap in your house: that is an established colony, and it is a removal job.
A basketball-sized mass of bees on a tree looks alarming, yet it is one of the few pest calls where doing nothing for a day is often correct. What matters is telling a passing swarm from a colony that has moved in. (Looking for Bee Swarm Simulator, the Roblox game? This page is about real honey bees.)
What are you looking at? Swarm, colony or something else
| What you see | What it usually is | Will it leave on its own? | What to do |
|---|---|---|---|
| A hanging ball or beard of bees on a branch, shrub, fence post or eave, with no comb | A honey bee swarm resting while scouts look for a home | Usually, within an hour to a day or two | Keep people and pets back; call a beekeeper on a swarm list |
| A steady stream of bees going in and out of one gap in siding, a soffit, chimney or wall | An established colony with comb inside the structure | No | Do not seal the hole; get a live removal or cutout quote |
| Wax comb hanging in the open, from a branch or under a deck | A colony nesting in the open, a habit UF/IFAS links to African honey bees | No | Stay away; call a registered beekeeper or licensed pest control operator |
| Single bees flying low over bare soil and entering small holes with soil mounds | Solitary ground-nesting bees, not honey bees | Not a swarm question | Usually leave them; see our ground bees guide |
| Large shiny black bees hovering at a fascia board with round holes | Carpenter bees | Not a swarm question | See carpenter bee vs bumble bee |
| Yellow and black insects at a paper nest or a hole in the lawn | Yellowjackets or other wasps | No, until frost | Check our wasp vs bee guide; this is pest control work |
The question that sorts most calls: is there comb? A swarm has none. Once bees have moved into a cavity, Clemson’s Home and Garden Information Center says they are no longer swarming, and the colony and its stores must be removed before the entrance is sealed.
What is a bee swarm?
Swarming is how a honey bee colony reproduces. UF/IFAS describes the process: the colony raises 10 to 20 daughter queens, and when those queens are in the late pupal stage the mother queen and about two-thirds of the adult workers leave and gather nearby while scout workers search for an enclosed cavity such as a tree hollow. Back in the old hive, the daughter queens emerge, fight until one remains, mate and start laying. One colony has become two.
People use “swarm” loosely for any angry mass of bees. Strictly, UF/IFAS says, it is a condensed body of bees between an old home and a new one, generally docile because it has no colony to defend yet.
Why do bees swarm?
Crowding. Iowa State and Mississippi State both call swarming a response to an overcrowded colony, and Clemson adds that in a crowded hive the queen’s pheromones no longer control the whole workforce. UF/IFAS ties the timing to food: European honey bees swarm in spring and early summer when pollen and nectar are plentiful, usually once a year. Sources disagree on how much of the colony leaves.
How big is a bee swarm, how long does it stay, and when?
Extension sources agree on the shape of the answer and disagree on the detail, so anyone quoting a single exact number is simplifying.
| Source | Swarm size | Main swarm season | How long the cluster stays |
|---|---|---|---|
| NC State Extension, Caldwell County | 10,000 to 40,000 bees | Spring | About 24 hours on average; an hour to 48 hours or more |
| Iowa State University Extension | Several hundred to several thousand workers, a few drones, one queen | Late spring and early summer | An hour to a few days |
| Mississippi State University Extension | Roughly basketball-sized mass | Late spring and early summer | One or two days, normally |
| Clemson HGIC (South Carolina) | Thousands of bees | March to May | A few hours or a day; some several days |
| MAAREC (Mid-Atlantic, University of Delaware) | About half the colony | March to June in Central, Southern and Western states; possible April to October | An hour or so, depending on scouting |
| Texas A&M AgriLife School IPM | Not given | Spring | Most move on within a day or two; a few hours to several weeks at the extremes |
Compiled by The Pest Control Brief from the named extension sources.
How big is a bee hive?
MAAREC describes a honey bee colony as several to 60,000 workers plus a few to several hundred drones and one queen, peaking in early summer. A swarm is a fraction of that.
The cavity scouts hunt for is specific. In Cornell nest box trials, Seeley and Buhrman found bees prefer 40 litre cavities over 10 litre ones and 15 square centimetre entrances over 75. That is about 10.5 US gallons behind an opening of about 2.3 square inches: a hollow tree, or a wall void behind a knothole or soffit gap. Sealing gaps matters more than anything you do to a passing swarm.
Are bee swarms dangerous?
In most situations, no. Iowa State says swarms are not highly dangerous under most circumstances, bees away from their nest are unlikely to sting unless provoked, and swarming bees fill up on honey first, which makes them less able to sting. NC State says swarms are not a public health concern, though anyone allergic to stings should keep a safe distance.
“Usually docile” is not “harmless”. Clemson warns that disturbed bees will defend the cluster, and Mississippi State says some swarms are irritable, so give all of them a wide berth. The calm does not last: Texas A&M notes that after about four weeks in a new nest, bees become defensive of it.
Are bee swarms aggressive?
Not in the sense people fear: a swarm has no brood or stored honey to protect. The risk comes from knocking it down, spraying or hosing it, or running a mower close by. UF/IFAS advises seeking medical attention for anyone stung many times, and calling 911 for an allergic reaction such as difficulty breathing or hives over large areas of the body. For sting care, follow your doctor or the CDC’s guidance on stinging insects.
Africanized honey bees: the southern caveat
African-derived honey bees reached the US through the southern tip of Texas in 1990. By 2007 USDA’s Agricultural Research Service listed eight more states: Arizona, Arkansas, California, Florida, Louisiana, Nevada, New Mexico and Oklahoma. In Florida, UF/IFAS dates the first record to 2001 near the Port of Tampa, with spread through the southern half of the state, and Texas A&M reported them in over half of Texas counties by 2013.
You cannot tell them apart by eye. Texas A&M notes they are slightly smaller than European honey bees and need lab analysis to identify, and UF/IFAS adds that their sting is no more potent. What differs is the defensive response, and the gap is large.
UF/IFAS says all honey bees, African or European, are considerably less defensive in a swarm state, but advises caution with every swarm. In these states: do not disturb it, remove it or spray it; call a registered beekeeper or pest control operator. If bees attack, UF/IFAS advises running in a straight line to a house or car, protecting your face, and not jumping into water.
Do bee swarms move at night?
Almost never. Mississippi State Extension puts it plainly: honey bees do not fly in the dark. Iowa State and MAAREC both say swarms leave during the warmer hours of the day. A cluster still hanging at dusk will very likely be there at first light.
Beekeepers use this: UF/IFAS’s guide for Florida beekeepers describes closing a hive box after nightfall, once the flying bees are inside. Do not inspect a swarm with a torch: Mississippi State notes bees disturbed at night fly towards light and crawl onto people and sting.
Where do bees swarm?
First, close to the old hive: NC State says swarms usually land on a nearby tree, shrub, fence post or building. Then scouts pick the final home, an enclosed cavity such as a tree hollow (UF/IFAS) or, less welcome, a wall, chimney or column (Clemson). NC State adds that most swarms people encounter come from managed hives, because few feral colonies survive varroa mites, small hive beetles and disease.
When is swarm season?
Spring into early summer across most of the US: March to May as the primary season in South Carolina, March to June in Central, Southern and Western states according to MAAREC, with occasional swarms from April to October. Secondary swarms occasionally follow later in the season and are less likely to succeed, Clemson notes.
Our iNaturalist data measure something different: most honey bee records are foragers on flowers, not swarms. Honey bees hold a steady share of records from March to August (an index of 78 to 105), rise to 158 in September, and are still recorded in January at 59, when bumble bees are at 9 and eastern carpenter bees at 4. That fits UF/IFAS’s account of a honey bee colony storing food to survive winter as a colony.
How to get rid of bee swarm?
For a swarm, usually let it go or let a beekeeper take it.
- Keep people and pets back and leave it alone. Iowa State says in most cases you need to do nothing. Mississippi State says do not knock it down, which only stirs up the bees.
- Call a beekeeper. County extension offices, state beekeepers’ associations and sometimes police and fire departments keep swarm collector lists. Collecting an accessible swarm is often free; our bee removal cost guide covers what you pay when it is not.
- Do not spray it. Clemson warns that spraying a swarm agitates the bees and increases stings, and Mississippi State notes a sprayed swarm cannot be saved.
- Make the professional call if it cannot wait. A swarm at a school entrance or busy shopfront may need dealing with at once, which Mississippi State says is a job for a pest control company. In Florida, UF/IFAS notes the property owner is responsible for an unwanted swarm.
- Use the time to bee-proof. Seal knotholes, gaps around pipes through walls and cracks in window framing, as Texas A&M lists. Other swarms will send scouts too.
When it becomes a removal job
Once bees have built comb in a wall void, soffit or chimney, Mississippi State says the problem will not go away on its own. Two mistakes make it worse: sealing the entrance, since the Texas Apiary Inspection Service warns sealed-in bees find another way out, possibly indoors; and leaving comb behind, which can attract another colony or other pests.
The Texas service also notes there is no bee removal licence in Texas and the business is unregulated, so it advises a written contract covering the work, price and timeline, plus references and liability insurance. That advice travels to any state. A cutout is structural work, which our removal cost guide prices.
Frequently asked questions
How long does a bee swarm stay in one place?
Usually from an hour to a day or two. NC State puts the average at about 24 hours, with a range from an hour to 48 hours or more, and Clemson says some swarms stay several days. The time depends on how quickly scouts find and agree on a cavity, and on the weather. A cluster that is still there after several days and has started building comb is no longer a passing swarm.
Should I spray a bee swarm with insecticide or water?
No. Extension services from Clemson to UF/IFAS advise against spraying a swarm with anything. Spraying agitates the bees, can increase stings, and kills a colony a beekeeper would usually collect for little or nothing. Hosing it down or knocking it off a branch has the same problem. If the swarm cannot be left, call a beekeeper or, where it is urgent, a licensed pest control operator.
Can you tell if a swarm is Africanized by looking at it?
No. African-derived honey bees are slightly smaller than European honey bees and look almost identical; Texas A&M notes that lab analysis is needed to tell them apart. Calm behaviour proves nothing, because UF/IFAS says all honey bees are much less defensive while swarming. In the southern states where they are established, treat every swarm and colony with extra caution and leave removal to a registered beekeeper or professional.
Why are bees going in and out of a hole in my wall?
That is almost certainly an established honey bee colony rather than a swarm, and it will not leave on its own. The bees have built comb inside the cavity and are foraging from it. Do not seal the hole, because the bees may find a way into the house. Call a beekeeper who does live removals or a pest control operator, and make sure the comb and honey are removed before the cavity is closed.
Sources
- UF/IFAS Extension, EENY568, European Honey Bee, Apis mellifera Linnaeus and subspecies, Mortensen, Schmehl and Ellis.
- UF/IFAS Extension, ENY-170, Living with the African Honey Bee, Ellis and Bammer, revised November 2024.
- UF/IFAS Extension, ENY-141, What to do about African Honey Bees: A Consumer Guide, revised October 2014.
- UF/IFAS Extension, ENY-2052, Best Management Practices for Live Bee Removals in Florida: A Beekeeper’s Guide, 2020.
- Iowa State University Extension and Outreach, What to Do When You See a Honey Bee Swarm.
- Mississippi State University Extension, What To Do If You Find a Honey Bee Swarm; and Bug’s Eye View newsletter, honey bees in and around the home, 2005.
- Clemson Cooperative Extension, Home and Garden Information Center, Frequently Asked Questions About Honey Bee Swarms.
- NC State Extension, Caldwell County Center, Why Bees Swarm, 2017.
- MAAREC, University of Delaware, Seasonal Cycles of Activities in Colonies.
- Texas A&M AgriLife Extension, School Pest News, Volume 12, Issue 2, April 2013: Bees.
- Texas Apiary Inspection Service, Honey Bee Removal Informational Document.
- Seeley, T. D. and Buhrman, S. C. (2001), Nest-site selection in honey bees, Behavioral Ecology and Sociobiology 49: 416 to 427.
- USDA Agricultural Research Service, Agricultural Research magazine, February 2007, Africanized honey bees.
- The Pest Control Brief analysis of iNaturalist research-grade records, pulled October 2026.
