Why do Bees Swarm?

Bees swarm. Swarming is natural and it is normal behaviour of healthy bees. But why do they do it? Let’s dive in!

Healthy honeybee colonies swarm as a way of multiplying when the conditions are right. This happens when the parent colony is getting too large for its current space and there is lots of food available to forage on. In short, things are so good they are running out of space! But when bees swarm they don’t all leave the hive. Instead, they split the colony into two or more groups, and one will remain in the hive: it is a way not just to find a new location, they do it to make more colonies and keep the species alive.

Before Swarming – the Triggers

Swarming is triggered by congestion in the hive. Because bees communicate via scent, or pheromones, when the hive gets congested, the scent of the Queen bee cannot be dispersed effectively throughout the hive. As a result of this lack of queen pheromone, bees start building queen cells. Like honeycomb, queen cells are made from beeswax, but they are larger than normal worker cells. Depending on the size of the colony and other factors, the bees will build somewhere between 4-30+ queen cells prior to swarming.

The queen lays a fertilized egg in most of the cells, and once the egg hatches into a larva after three days, the queen-larvae receives lots of attention and very large helpings of royal jelly. (This allows her ovaries to mature, and once she emerges after pupating, she is able to mate and lay eggs.) The queen-larva enters pupal stage on day nine, when the worker bees seal the cell. This is a critical point for swarming as the first swarm usually leaves the hive soon after the first queen cell is sealed.

What Happens after the Swarm Leaves the Hive?

This first swarm is called a Prime swarm and contains the ‘Old’ Queen and up to half of the worker bees. They will leave the hive together, and cluster somewhere close to the hive, usually on a tree or fence post or similar. The swarm will then send out scout bees to investigate all possible locations in the area that may be suitable nesting spots. They usually look for cavities of about 40liters, a few meters up off the ground with one or several small-ish entrance holes that they can easily protect.

After investigating, the scout bees will come back to the swarm and ‘tell’ them about the different sites (by dancing the waggle dance!) and more bees will go off to investigate. At some point they have convinced enough of their fellow bees about the suitability of one particular site and the swarm will take off together and fly straight to their new home.

Casts and Virgin Queens

A second and even third and more swarms can emanate from the original colony about seven day after the ‘old’ queen has left (16 days after the queen laid and egg in the queen cell). This is when the first of the virgin queens emerge from her cell after pupating. Sometimes several virgin queens will be contained in a swarm. These swarms are often referred to as secondary swarms or casts. Depending on the size of the swarm, there are also hundreds if not thousands of female worker bees in the swarm. Often you will find some male bees, drones, in with the mix as well.

When Does Swarming Happen?

Swarming can happen throughout the active season, but late spring and early summer is considered swarming season for honeybees in Ireland. We usually encounter a lot of swarming during a spell of hot, dry weather, especially if the weather has been poor leading up to it.

Swarming In Short

So, in short: A swarm is a compete and fully functioning honeybee colony that has left its hive in search of a new home. A swarm will emerge from a colony of bees, leaving a portion of bees behind in the original colony, including either a virgin queen or a queen cell which will become a queen. Hence the colony is split, and both parts will have what it takes to carry on life as individual colonies. Bees swarm in order to increase the number of colonies and ultimately to ensure the survival of the species.

PS. Let’s help protect our bees and let swarms live! Contact your nearest beekeeper if you spot a swarm clustering or on the move and they will help to remove it safely without harming the bees.

Hanna Bäckmo

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