Swarms of bees that sparked a stir in Bangor may have originated in hollow trees in the town's Ward Park.
Beekeeper Phelim Breen, who collected one of the swarms, said the trees were host to a number of rare wild colonies of honeybees. These colonies could originally have been founded by bees that had escaped from domestication.
Mr Breen was called out after swarms of bees settled on property in the town over the Bank Holiday weekend.
Amanda McCullough said a swarm gathered on the garden wall of her house, adding: "At about lunchtime, the lady next door was getting married and we were outside to see her dress when the air became thick with bees.
"Within half an hour they had settled on my wall, but I thought they were wasps originally."
The bees have moved on, but another swarm touched down on the windscreen of a car parked near Hamilton Road Presbyterian Church, a couple of hundred yards from the first swarm.
"The congregation had to take refuge in the church while the bees were swarming outside," Mr Breen said. The swarm had landed on the windscreen of the car and stayed overnight. When Mr Breen arrived he persuaded them into a box for removal.
"They all walked in very easily," he said.
Mr Breen said scout bees search for a new home and perform a dance on their return to recruit other bees to visit the potential nesting site.
"They may pick out up to six or seven sites and once a consensus is agreed on one particular site, they all take off," he said.
"It's quite a spectacular view and it scares the living daylights out of a lot of people. You could get between 15,000 and 20,000 bees in a swarm. They may not look it but these swarms are very organised.
"On the perimeter, the scout bees are busy putting down scent and directing the queen and the others where to go. Then the bees go into the new site and start cleaning and sterilising it with an antibiotic called propolis. This is made from the resin of trees which they chew up and add their own antibiotics to.
"Then they start building the honeycomb and the queen starts laying eggs and the whole system starts up again.
"There are a number of trees in Ward Park with hollow trunks and it's possible a number of old colonies in those trees may have swarmed," Mr Breen said.
If you see a swarm, check they are honeybees rather than wasps. The swarm will probably be about the size of a full-size rugby ball and will hang in a tree or under the leaves until they have found the kind of home they want.
It is important to have the swarm removed quickly before it becomes established. A list of collectors is at the www.ubka.org website.
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