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Bee keeping in Barnsley, South Yorkshire

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Facts & Tips - Swarms

Beekeepers often take great care to avoid letting their bees swarm. To the beekeeper, a swarm represents a loss of bees resulting in less or no honey production and a reduced ability to over-winter colonies due to a smaller colony size. Swarming may also disrupt plans to split hives and increase colony numbers. Swarming is something that most, if not all, beekeepers will suffer from and seek to control through swarm control or prevention.

In the is section we look at why bees swarm.

What is a swarm?

A swarm of bees is typically a new colony of bees in the process of searching for new location to establish a nest. The swarm is normally composed of a queen, several thousand worker bees and a number of drones.

A swarm is a result of the natural process of expansion by bees with swarms leaving established nests or hives to set up home elsewhere. Bees have been doing this for millions of years.

A swarm of honey bees can vary in size and be from something like 2 or 3 thousands bees to 20 or 30 thousand. The number of bees in a swarm tends be related to the size of the original colony from where it has come and how many swarms have left the colony before. The first swarm to leave the hive (the Prime Swarm) is the largest and can contain 50-60% of all the workers. The prime swarm is often followed by one or more secondary swarms (casts) each with a smaller number of worker bees. Eventually, the original colony may be left with only 10-25% of the bees it started with.

The swarm tends to go through a few different phases whilst it finds a new home. The queen is often forced out of the hive by the workers, who guide her to an appropriate local resting place such as a nearby fence post, tree or hedge. The workers and drones follow the pheromones of the queen and the swarm undergoes a period of settling with more bees joining from the original colony. Lots of bees will be flying for some time while the swarm clusters around the queen.

If left undisturbed the swarm tends to remain calm and tightly massed, while scout bees fly off to find a suitable, permanent home. Depending on how quickly the scout bees find a suitable hollow, the swarms may remain in place for 2 days or so.

Once a scout bee has found a suitable location, it will perform a dance giving details of the location to the other bees. Additional scouts fly off to investigate and report back with their own dance. The strength of the dance (in terms of numbers of bees performing it and strength of the movements in the dance) determine whether or not the swarm flies off to the newly found location. Once they have decided, the bees fly off en masse, leaving little trace behind them.

Is a swarm dangerous?

Usually, swarming bees are not aggressive however, the amount of risk posed by a swarm does vary. When settled in a tight cluster the bees are often quite docile and can often be approached without much problem. This is the point at which they are at their easiest to catch by the beekeeper. The swarm can, depending on where they are located, be knocked or brushed into a box with relative ease and without too many taking to flight. If however, the bees are actively flying around in large numbers, e.g. when the swarm is just settling, the bees can be a bit aggressive. A swarm is quite vulnerable and will defend itself if interfered with. However, unlike swarms portrayed in certain movies, swarms do not pester, chase or attack people. The best thing to do is leave them alone or move away from a swarm that is actively flying around - a swarm is only a temporary phenomenon and will move on after a day or so. A local beekeeper might be able to come out and collected a swarm for you.

When do bees swarm?

Honey bees typically swarm (in the UK) between early May and late July. An early, warm spring may cause bees to swarm a little earlier in some places. The timing of swarming will largely depend on the availability of food and the bees will respond quite quickly to an abundance of spring forage.

Why do bees swarm?

Honey bees are impulsive creatures, reacting to stimuli in their environment. The colony will grow according to increasing day length and increasing availability of food (nectar and pollen). The bees aim to maximise the size of their colony to coincide with the maximum availability of food - in July. This not only allow the bees to collect the maximum possible amount of nectar to store as honey for the winter, it maximises their chances of increasing their species by swarming. The bees react to overcrowding as the colony grows during the spring. Chemicals produced by the queen (queen substance) that normally inhibit swarming become more dilute. Also signals, (to let the colony know the queen is present) produced by the queen as she vibrates her body in short bursts, become less effective at inhibiting swarming, due to her range within the hive increasing - the bees detecting a reduced frequency of these bursts. The instincts of the bees kick in and they make incipient queen cups. When the queen lays eggs in these, the workers form these into new queens.

The workers may produce anything from 1 or 2 queen cells to 6 or 7 depending on their genetics (swarming tendency) and the availability of food at the time. It is logical that if their is more food available, then more swarms will survive, so more are produced. Of course, bees don’t have logic, but millions of years of evolution within changing environments have led to an innate ability to react to times of surfeit and deficit.

When the workers have decided to allow a cells to remain in a queen cup, they will begin to build up the sides to form a queen cell. The newly hatched larva is fed an enriched diet called royal jelly which allows the larva to grow more rapidly and to a larger size than worker or drone larvae. 16 days after the eggs was laid the new queen will emerge.

The existing queen is ushered out of the colony usually around the time the first queen cells is capped over (8 days after laying). The workers will have prepared her over the few days running up to this point. They slim her down with smaller amounts of less rich food so that she is better able to fly. This first “prime swarm” often comprises around half the entire colony. The remaining colony will keep issuing smaller swarms (casts) until it either has one queen cell left of has reduced in size to a point where the worker dictate that no more swarms can leave. If, at this point, there are 2 or more queen cells left, the first to emerge will kill the other queens while they are still in their cells. If 2 emerge at the same time, they will fight to the death (by biting and wrestling rather than stinging) until one remains.

Where do swarms go?

Swarming bees will mainly seek out some kind of cavity in which to make their new home. Wild bees would typically seek out hollows in trees and in rock faces anywhere from 3 to 10 metres from the ground. The hollow must offer sufficient protection from the elements and the entrance must be small enough to defend. The bees will often use propolis to reduce entrance sizes to around 1-1½cm in diameter. The bees will seek out a hollow which is large enough to accommodate a large colony - which will be anything of 40 Litres upwards. For this reason, honey bees do not occupy bird boxes (whereas bumble bees often do). Occasionally, swarms will make their home in open spaces beneath some kind of overhang.


             Wild colony in an out building.