Alaska News

With arrival on Kenai Peninsula, cluster flies make first Alaska appearance

Among the insects abuzz at the end of Alaska's unusually warm winter is a fly previously undocumented in Alaska -- Pollenia, commonly known as the cluster fly.

Since mid-February, cluster flies have been showing up in abundant numbers on buildings at or near the Kenai National Wildlife Refuge headquarters in Soldotna, said Matt Bowser, an entomologist based at the refuge. He collected 35 specimens between mid-February and mid-March -- from building walls, from snow, from cobwebs and from various sunny surfaces -- and said many more were hanging around.

Up to now, there had been no reports of cluster flies in Alaska, said Bowser, who detailed his findings in the latest newsletter of the Alaska Entomological Society. But the flies have previously been documented as close as British Columbia and are among the few insects that overwinter in cold climates, he said.

"So it's not a big surprise or jump to see it here," he said.

It is quite possible that cluster flies have been in Alaska for a while, though under the radar, Bowser said.

"They've probably been here a few years, at least a couple of years," he said.

Cluster flies are native to Europe -- including cold areas like Scandinavia -- but those of this type became established on the East Coast in 1958, Bowser said. They have been making their way west since then.


The flies look similar to ordinary houseflies but are a little more "woolly" looking, Bowser said. The adults have some distinctive golden hairs and are bigger than most ordinary houseflies, according to Penn State University's College of Agricultural Sciences.

Their common name comes from their tendency to cluster together -- on sun-baked walls, on windows and in indoor wintering spots.

There are six cluster fly species that have been identified in North America. Those found in and around the Kenai Refuge headquarters building were of the species Pollenia vagabunda, Bowser said. But he said he would not be surprised to find additional species, especially in places like Anchorage and Juneau, where there are more introduced species in general.

The flies do not sting people or spread disease, he said. "They tend to be just a nuisance," he said.

It is unknown whether their presence might have ecological impacts, he said. Some cluster flies are parasites on earthworms when in larval form and later prey on earthworms, he said.

But, Bowser noted, "Earthworms are not native (to Alaska), either."

Non-native earthworms can alter food webs in soil, thus harming ecosystems in northern forests around North America, according to past research, including research by Bowser at the refuge. Almost all of the earthworm species in the region have been introduced from elsewhere, Bowser said.

Cities like Anchorage and Juneau have an abundance of introduced earthworms, which could be hosts for cluster flies, he said.

Yereth Rosen

Yereth Rosen was a reporter for Alaska Dispatch News.