UPDATE: The bees have been found and returned to their home in Halifax.

When Lorraine Simmons-Yerian heard a very loud hum coming from her backyard Tuesday afternoon in Halifax, she looked out her window and saw a "swirling tornado of bees."

"These guys went up above the tall pine tree and over my house and kind of disappeared within two minutes," said Simmons-Yerian, a member of the Halifax Honeybee Society.

She estimates more than 20,000 of her honeybees fled the hives she keeps in her backyard in the Fleming Heights subdivision and thinks the warmer weather could have been a factor.

"It feels more crowded [in the hive], just like us in the house with no air conditioning, and so they make the decision to leave on a nice day to really increase their chances of survival," she said.

Crowded, hot hives

When bees abscond, they usually don't go very far — 20 metres at most, said Simmons-Yerian. But this time they swarmed out of eyesight.

In the past, she's been able to catch them fairly easily. The bees typically will swarm and land nearby on a branch, where they surround the queen, form a big ball and then move a short distance again.

"It's actually a very natural process for bees. They're incredible insects. They will sort of scope out the whole hive, see if it's getting crowded, the queen will lay an egg to raise a new queen — that would be one that's going to replace her — and then they make a plan," explained Simmons-Yerian.

"They exercise the queen, they chase her around the hive and just before they're going to swarm, usually on a hot day like today, they all gorge on honey so they're super well-fed for the trip and then about 60 per cent of the bees just leave the hive in a very controlled manner." 

Don't approach the swarm

The bees usually swarm on fence posts or branches, but Simmons-Yerian said she has no idea where hers have landed this time.

After a swarm, the bees are "the calmest and most docile of any time," she said, and generally will not sting unless they're provoked. That said, she discouraged anyone from going near a swarm unless they are trained to deal with one.

"Don't panic, just give me a call and I would be happy to come and get them," she said. "I'm hoping to hear that somebody has seen the swarm so I can go and get it and bring it back home."

She said collecting a swarm often means donning protective gear and scooping the bees into a box or lowering them into the box if they are attached to a branch.

With files from CBC Radio's Mainstreet