Bee swarms on the rise as weather warms, but impact of varroa mite predicted to reduce swam frequency

Reports of bee swarms in South Australia’s South East have increased significantly after a “hectic” spring, but the ongoing threat of varroa mite to feral bee populations has potential to near-eradicate swarms in coming years.

Pest controller and apiarist Sam Shaw said demand for swarmed bee removals has increased about tenfold from two or three calls per month a few years ago to 20 or 24 per month this year.

“So far it’s been pretty hectic,” he said.

“We’ve had a good spring so far. I know [the swarming season] came a bit later last year.

“It just completely depends on the weather as well and it depends on how much room the queen has in a hive.”

Swarming creates new colonies

Australian National University evolutionary biology professor Sasha Mikheyev said swarming was how honey bees reproduced.

Professor Mikheyev said significant rainfall over the past three years had led to increased food for bees.

“When conditions are good, the honey bees raise plenty of young. They have many new individuals and lots of food,” he said.

“That’s when they decide that they can split and both halves of the original colony will keep growing. The mission is reproduction.

“They’ve had opportunities over the past few years to build up their honey stores and also to build up their worker numbers.

“What we’re seeing now could be a manifestation of that.”

Although swarms more often form due to favourable conditions for bees, Professor Mikheyev said bees would also abandon a hive if it were diseased.

In areas infected by varroa mite, this could lead to an increase in swarming behaviour.

“If a colony is very heavily infested, they will sometimes fly off,” Professor Mikheyev said.

“Varroa tends to be around the brood and only a small fraction of them will go onto the honey bees and be transported, so swarming is a short-term solution for honey bees to deal with varroa.”

But in the long-term, scientists say the impact of varroa on feral European honey bees could reduce swarm frequency.

“The swarms that we see now, we might not see quite as many of them a few years from now,” Professor Mikheyev said.

Domesticating swarms

Mr Shaw said one benefit of beekeepers domesticating swarmed colonies was that it allowed for captured feral bee populations to be supervised more closely for varroa and other diseases.

“We leave them for a week or so just to calm down and for them to get a bit settled, and then we’ll do frequent inspections on them, usually weekly but maybe every fortnightly,” he said.

“We have to do yearly testing for varroa mite and any other hive diseases.”

Professor Mikheyev said national regulation for stricter management of supervised colonies, kept by both commercial and hobby beekeepers, would soon be enforceable.

“They’ll receive some sort of chemical treatment that will help keep the mites in check, otherwise the colonies will die,” he said.

“The feral bees of course will get no such treatment and it’s not clear how many of them will die, but it’s very likely to be more than 95 per cent.”

While swarms were typically timid, Mr Shaw advised people to stay away if they came across one.

“It completely just depends on if they’re aggressive or not,” he said.

“You’ll find out pretty quick if you’re walking past and they are aggressive.

“Most of the time a swarm can just be resting there for a brief moment and they could be gone within a couple of hours.”