Invasion of black flies has threatened the population of Wisconsin loons, forcing them to abandon their nests in large numbers. The pesky biting insects have caused 80% of the black and white birds to flee their nests in Vilas County and more than 70% of nests in Oneida County.

The rate at which black flies have emerged this year is the highest in last 25 years, said Michael W. Meyer of the Wisconsin Department of Natural Resources.

The condition has become really worrisome for the loons as it will take a longer time for them to re-nest, which means the resulting chicks will not have enough strength to survive cold weather in the fall. Survival of loon chicks is highly dependent on incubation of eggs by father and mother loons for around 30 days. Loon chicks start flying after completing 11 weeks of their life.

Meyer said the biting flies have special liking for loons. The scientific name of black biting flies is Simulium annulus. A combination of a cold Wisconsin spring and quick arrival of summer warmth in May has led to a record year for the black fly.

“There’s always a burst that comes out in May. This happens to be one that is particularly devastating”, said Walter Piper, a researcher at the School of Earth and Environmental Sciences at Chapman University in Orange, California.

About 1,200 loons reside in Northern Wisconsin. This year, number of loons is likely to drop by 30% because of leaving their nests over fear from black biting flies.