Flathead Suffers From Five Years Worth of Mosquitoes at Once

By Beacon Staff

A mosquito swarm has descended on the Flathead, the likes of which hasn’t been seen in years. Arriving with the warm weather, the gossamer-winged pests have burdened every barbecue with their buzzing bloodlust. The attack of the “skeeters” forces those who wish to enjoy the long summer evenings to choose between fleeing indoors or suffering the red, itching bites left in the wake of these irritating insects.

For anyone wondering if this summer’s mosquitoes are worse than usual, the answer is a resounding yes. As for the reasons why the mosquitoes are so bad this year, Flathead County Mosquito Control Coordinator Bruce Gunderson attributes it to a cool, wet spring where snowpack increased between March and May, rather than decreased. Then, when hot weather hit in June, the valley’s rivers grew so much they activated mosquito eggs high on the banks that have been laying dormant for years.

“We just really had an uphill battle with late runoff and very warm weather – it triggered a huge hatch,” Gunderson said. “The whole valley this year is just ripe for mosquito production.”

These floodwater mosquito eggs can lay dormant for as long as five years. While incapable of carrying the West Nile virus, floodwater mosquitoes are often more aggressive – and now they’re everywhere.

A sample of pupae and larvae collected by Jacqueline Hadorn.

“We’re essentially going to have five years of eggs hatching all at once when we have this high water,” Gunderson said. “We kind of just had the perfect storm.”

As the rivers remain high, and continue to push up groundwater around the Flathead, Gunderson spends his days mapping areas of standing water, then treating them with larvicide. He estimates he has mapped more than 410 acres of mosquito-producing waters in the Flathead, adding, “there’s probably five times that much water out there that we haven’t found.”

Gunderson also stays busy taking calls from the public to treat standing water, and on a typical afternoon had 26 service requests. The most mosquito-plagued regions of the valley currently include anywhere near rivers. Kalispell’s Lawrence Park, which has a marshy, sloping area along a backwater of the Stillwater River, is a huge producer of mosquito larvae, Gunderson said. Other trouble regions include Evergreen, due to its high water table, and agricultural areas of the Lower Valley.

Flathead County uses two mosquito treatments: The first, Altosid, is dropped into catch basins and areas of standing water to prevent larvae from developing into mosquitoes, by mimicking the insect’s growth hormone. Gunderson began dropping Altosid in late April, and estimates he has dropped over 560 pounds around the valley. At about $125 to properly treat an acre of land, Altosid isn’t cheap, and Gunderson uses it sparingly – but said killing mosquito larvae is the most cost-effective way to deal with the pests.

Once the mosquito season begins, Gunderson drops his second defense, a natural bacterium called Bacillus, or “Bti,” a spore attached to corncob chips which is toxic to mosquitoes and black flies when eaten. He estimates he has dropped 700 pounds of Bti, so far. Neither mosquito treatment is considered harmful to humans.

But both of these treatments focus on killing mosquito larvae, and once grown adults take to the air, the task of killing them becomes much more difficult. Flathead County stopped aerial spraying of chemicals to kill mosquitoes in the mid-1990s, but Gunderson currently has a request before the county Mosquito Control Board to perform aerial spraying of larvicide next year, “because we really do have so much acreage to cover.” Aerial spraying would also be safer, he added, for him and other county workers who spend their time slogging around bogs looking for mosquitoes, and have stepped on submerged barb wire, pallets, exposed nails and other hazards.

But if there is one good thing about the floodwater mosquitoes, it is that they don’t carry the West Nile Virus. While those mosquitoes only account for about 2 percent of the mosquitoes in the Flathead, they have just begun to hatch. Gunderson has been collecting samples of the mosquitoes, a genus known as Culex, and sending them to the Department of Animal Range at Montana State University for tests. Positive tests are sent from there on to the Department of Public Health and Human Services in Helena. Positive West Nile samples from the Flathead are rare and shouldn’t be affected by the high number of floodwater mosquitoes hatching.

“We haven’t seen West Nile in the Flathead Valley for two years,” Gunderson said. “I have no idea what the outlook is for this year – no district ever really does.”

So for now, Gunderson continues his testing, mapping, and killing of mosquitoes. It’s a fight that, this year, sometimes feels insurmountable. He invites the public to call him for tips and help with mosquito treatment at 751-8145.

Related: Surviving the Swarm

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