The Carlisle Mosquito Online

Friday, May 19, 2006


A swarm similar to this one took up temporary residence on Acton Street. (Photo by Ernie Huber)

Biodiversity Corner Honey Bee Swarm

It was two weeks ago today, before all the rain, when Marty Schafer of Acton Street heard a huge buzzing up in the pine trees at about 8:30 a.m. He saw a lot of insects flying around in a rather disorganized way and remembered hearing about honey bee swarms in his childhood but had never seen one. He knew that if it was a swarm, the bees would be congregating somewhere, and with the help of binoculars he found the spot high up in a pine where two branches divided — too high for a good photo. "At first there was just a whole bunch all landing in one spot. Over time though, fewer and fewer were flying and more and more had landed on the spot. At times a whole batch of the honey bees would fall off the spot — almost like icebergs falling off glaciers. Then they would climb back on. Later in the day, about 2 p.m., they were still there, and we showed some visitors. Then we looked again at 4 p.m., and they were all gone!"

Why honey bees swarm: Swarming is the instinctive reaction to overcrowding in the current nest. It is most common in May and June. The old queen and typically about half the workers leave the nest en masse and establish a new colony, usually in a hollow tree unless man intervenes. A daughter queen and the remaining workers continue to live and work in the original nest. Skilled beekeepers can prevent swarming by giving the bees plenty of room; they can also collect a swarm and establish it in a new hive. The folk rhyme "a swarm in May is worth a load of hay; a swarm in June is worth a silver spoon; a swarm in July isn't worth a fly" explains that there won't be much honey this year from the swarm captured in July.

House hunting: The swarm, which could have up to 30,000 bees, needs to find a home as soon as possible. The bees, or at least the scouts, seem to have a built-in sense of what is adequate and what is preferential in a nesting site. An excellent site would have a cavity of around 20 liters capacity; it would be several yards above the ground; it would have a south-facing opening not larger than five square inches and the opening would be at the base of the cavity. The intriguing process by which several thousand bees reach a decision on a new home, usually within a day or two, has evolved to a point where they almost always "agree" on the best site of all the alternatives. A few hundred bees scout for sites, frequently returning to the swarm to learn what other bees have found or to communicate their own findings. If they find a potential site, they advertise it with a dance.

The waggle dance: Honey bees perform a very specific set of movements called a "waggle dance" to tell other bees in a hive where the best food sources are. They perform the same dance, right on the surface of the swarm, to indicate both the location of a possible nest site and its level of excellence. The bee runs in a straight line while waggling her abdomen from side to side. At the end of the run, she circles back to where she started and begins another circuit. (I've not seen it myself but American Idol's Taylor Hicks comes to mind.) The angle of the line away from vertical indicates direction; the length of the waggle run indicates distance; the number of circuits in the dance indicates quality.

Making the decision: The thought of a clustered mass of thousands of homeless bees rapidly reaching a consensus boggles the mind, but this is only part of the process. The site itself is chosen by reaching a quorum at the site. The scouts are mysteriously able to sense the quorum, and this time when they return to the swarm they trigger flight preparation activity in the whole swarm. In the hour or so that it takes the swarm to warm their flight muscles, enough scouts have achieved consensus on where they are going to be able to "steer" the swarm to the chosen site. The optimal quorum size in the trade-off between speed and accuracy site selection seems to be somewhere between 10 and 20. This sounds small but at any given time most of the scouts are either at the swarm or in the air, so this number at a site, at the same time, is significant.

What should you do: If you see a swarm you might want to notify a beekeeper who can decide if it can be collected. Do not spray it. We need the bees for good yields in fruit and veggie crops, and bee populations have dropped due to parasitic mites. The swarm, if not collected, will fly off to its new home within three days. In the meantime, the bees do not engage in the defensive behavior they use at a nest to protect their young and their food. If not unduly provoked, they will keep to themselves.

Sources: First-hand report from Marty Schafer's wife, Jan Sacks; U. of Nebraska Entomology Dept at; Thomas D. Seeley et al., "Group Decision Making in Honey Bee Swarms," American Scientist, May-June 2006,

Please feel free to write the Biodiversity Corner. The only requirements are that the topic exists in the wild and was seen in Carlisle. Or send potos, sightings or ideas for the column to Kay Fairweather at 392 School Street, Carlisle, MA 01741, or e-mail

2006 The Carlisle Mosquito