A swarm cell is a special queen cell that honey bees build when a colony is preparing to split in two. Inside it, worker bees raise a new queen who will stay behind and lead the original hive after the existing queen leaves with a large group of bees to establish a new colony elsewhere. For beekeepers, finding swarm cells on your frames is the clearest sign that swarming is underway or imminent.
Why Bees Build Swarm Cells
Swarming is the natural way honey bee colonies reproduce at the colony level. When conditions are right, typically in spring, an abundance of flowers producing pollen and nectar fuels rapid population growth. The hive fills up with bees, brood, and stores, and congestion becomes a problem. At that point, the queen signals worker bees to begin preparations for swarming, and they respond by constructing new queen cells along the edges of the comb.
The goal is straightforward: the old queen will leave with roughly half the colony’s workers to find a new home, while a freshly raised queen from the swarm cell takes over leadership of the bees that remain. It’s colony-level reproduction, not a sign that something has gone wrong. A healthy, thriving hive is actually the most likely to swarm.
Where Swarm Cells Appear on the Frame
Swarm cells are built along the margins of the comb, most often hanging down from the lower edges of the frames. This location is one of the quickest ways to distinguish them from supersedure cells, which bees build on the face of the comb when they need to replace a failing or missing queen. Most beekeepers report finding three or more swarm cells at a time, often at different stages of development. Supersedure cells, by contrast, usually appear in groups of one to three.
A completed swarm cell looks like a peanut in size, shape, texture, and color. It hangs vertically, open end facing down. Before the queen lays an egg in it, the structure is smaller and open-ended, resembling a thimble. At this stage it’s called a queen cup, and queen cups are a normal, routine part of colony life. They don’t necessarily mean swarming is happening. The critical distinction is what’s inside: once a queen cup contains an egg or a larva floating on a bed of milky-white royal jelly, and workers are actively building it out into a full peanut-shaped cell, it has become an active queen cell. Finding these along the bottom edges of your frames is the unmistakable sign.
What Makes a Queen Instead of a Worker
The larva inside a swarm cell is genetically identical to any worker bee larva. The difference is entirely nutritional. All bee larvae receive royal jelly, a protein-rich secretion produced by glands in the heads of young worker bees, for the first three days of life. After that, worker-destined larvae are switched to a diet of honey and pollen. Queen-destined larvae continue receiving royal jelly exclusively throughout their entire development. This continuous feeding triggers a completely different developmental pathway, producing a larger bee with functional ovaries capable of mating and laying eggs.
Development Timeline
A queen develops faster than a worker bee. From the moment the egg is laid, it takes 16 days for a queen to emerge. The egg itself hatches into a larva after about three days, and from that point, the new queen emerges roughly 13 days later. Workers cap the cell around day 8 or 9, sealing the developing queen inside to pupate.
This timeline matters for beekeepers because it determines how much warning you get. If you find uncapped swarm cells with young larvae, you still have several days to act. If the cells are already capped, the colony may swarm at any time. Once a virgin queen emerges, she will often destroy the remaining queen cells, so timing is critical when managing the process.
Swarm Cells vs. Supersedure Cells
Both swarm cells and supersedure cells produce queens, but the colony’s motivation is different. Swarm cells mean the colony is growing and preparing to divide. Supersedure cells mean the colony has determined that the current queen is aging, sick, injured, or missing, and needs a replacement. The two types look physically identical once completed, so location and number are the main clues.
- Location: Swarm cells hang from the bottom edges of the frames. Supersedure cells extend outward from the face of the comb.
- Number: Swarm cells typically appear in groups of three or more, often at varying stages. Supersedure cells usually number one to three.
- Context: Swarm cells appear in crowded, booming colonies during the spring buildup. Supersedure cells can show up any time the queen’s performance declines.
How Beekeepers Spot Them Early
Because swarm cells appear on the lower edges of frames, many beekeepers use a quick-check method: tipping up each brood box and looking at the underside of the frames all at once. A puff of smoke can shift bees out of the way so you can see whether any queen cups or developing queen cells are hanging from the bottom bars. Since finding cells at this stage doesn’t give much advance warning, these checks need to happen frequently during swarm season, roughly every seven to nine days in spring.
What to Do When You Find Swarm Cells
Finding swarm cells doesn’t mean you’ve already lost the swarm. If the cells are uncapped and the queen is still present, you have options. The simplest preventive step is adding supers (extra boxes) early in the season to give the colony more room, but once swarm cells are being built, that alone is unlikely to stop the process.
The most common intervention is an artificial swarm, which mimics what the bees were going to do naturally but keeps everything under the beekeeper’s control. In a Pagden artificial swarm, you move the queen to a new box in the original location. The flying bees return to her there, while the brood and nurse bees stay in the old box and raise a new queen from the existing swarm cells. A vertical split follows the same logic but stacks the two halves on top of each other, using less equipment. A third approach is creating a nucleus colony: you place the queen, some bees, and a few frames of brood into a small nuc box, and let the original colony raise a new queen on their own.
If the colony has already swarmed and you discover capped cells with no queen in the hive, the priority shifts. At that point you need to ensure only one new queen emerges successfully. Leaving multiple capped queen cells can lead to the first virgin queen destroying the others, or to secondary swarms (called afterswarms) that further weaken the colony. Many beekeepers reduce the cells down to one or two of the best-looking capped cells to give the colony the strongest chance of producing a healthy, well-mated queen.