Loons and blackflies

Emily Stone

The loon nest at left is plagued by black flies who have driven the parents to deeper water – away from their incubation duties Just before the black flies hatched, this loon began incubating two eggs on Lake Namakagon. The black fly that attacks loons does not bite humans, although the one at right landed on my cheek. The flies likely identify loons by the smell of the oil used for preening their feathers. Photos by Emily Stone.

Ratchet straps, paddles, life jackets, and cameras were flying everywhere as I rushed to unload my kayak from my car and get it to the lake. Nipping at my heels – nd my ears, neck, temples, wrists, and eyelids – were swarms of black flies.

I snorted one out of my nose, and blew another off my lips, but the rest I tried hard to ignore. Taking time to swat them would mean delaying my escape to the water.
Finally, with a couple of quick paddle strokes I pulled away from the landing and into a fresh breeze.

Mineral Lake sparkled in the late afternoon sunshine, and baby leaves on the surrounding trees glowed with the promise of new life. As I paddled into a headwind, the last of my tormentors disappeared. With a deep breath, I found peace.

Gliding along, my mind drifted off to another lake – Lake Namakagon. While biking around it on May 14, I was ecstatic to spot the distinctive shape of a loon’s head nestled among the grasses on a small island, visible from the road.

Thrilled that I’d brought my camera, I zoomed in and snapped a few shots. After a few seconds of stillness, the black flies swarmed – the first of the season for me.
The following day was sunny, calm, and perfect for paddling, so I launched from my house and headed toward the bay that holds the nest – hoping to get another glimpse of the loon. Not wanting to disturb a nesting bird, I once again zoomed in with my camera, to check out the nest from afar.

No distinctive silhouette stuck up from the island, although I heard a single, plaintive wail from the far side of the bay. Where had the loons gone?

Drifting closer, I could soon see that the nest was not empty after all. Two large, dark eggs gleamed in the sunlight, and surrounding them was the thickest cloud of black flies I’ve ever seen.

Simulium annulus is a species of black fly that focuses their insanity-inducing, bloodsucking behavior entirely on loons. They crawl around the loon’s eyes and bill, use special claws to burrow into feathers, and raise welts so big that they ruffle up the loon’s usually sleek neck.

With jagged, knife-like mouthparts, black flies tear into tender skin, rupture capillaries, and create a pool of blood. Chemicals in their saliva numb the site and prevent the blood from coagulating as they lap it up.

Loons in a cloud of black flies suffer from blood loss, irritating reactions to the anticoagulant, and blood-born parasites and viruses transmitted by the flies.

Without hands to swat them away, a loon’s only options are to sit and endure, or to dive and leave the eggs cold and unprotected. The embryos can survive some exposure if the parents return frequently to incubate, but there is a limit, and many will not survive.

Luckily, in a normal year with warm spring weather, all of the black flies hatch, seek a blood meal, mate, and lay eggs in just a few days. The brief scourge can be endured, and most loon nests are unaffected.

In cool springs, though, like the one we’ve just had, some female black flies delay their quest for a blood meal while waiting for better weather, and others stick to the schedule. This means that loons must endure the plague of black flies for a longer period of time.

Do you remember the spring of 2014 – the year of the Polar Vortex – when lakes were still locked in ice for fishing opener? That spring, 70% of loons’ first nest attempts failed.

Walter Piper has been studying loons on northern Wisconsin lakes for more than 20 years, and it was the worst rate of nest failure he’s ever seen.

Although ice-out dates this spring weren’t that extreme, our cold April may have produced the same result. Walter Piper – monitoring remotely from California – wrote about a black fly outbreak in his recent Loon Project blog.

Linda Grenzer, one of LoonWatch’s star volunteers, just reported that every loon nest she monitors is coated with black flies and abandoned.

Sadly, my observation is just one more depressing data point.

The good news is that loons have been around long enough to figure out some coping strategies.

Even when a pair abandons the nest, they can still try again, after the black fly numbers have diminished. However, the second attempt is more likely to produce just one chick instead of two.

Loons have even learned that when eggs fail due to black flies, they can reuse the same nest location. In contrast, losing eggs to a nest predator like a raccoon – who would not be gone in a week – would necessitate moving the nest in an attempt to find a safer location.

So, in the face of potentially deadly parasites, loons, as well humans, are weighing our options carefully this spring. For both of us, escaping to the middle of a lake to avoid disease-carrying crowds seems a pretty good idea.

Emily’s second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at cablemuseum.org/books. Or order it from our friends at redberybooks.com to receive free shipping! For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is currently closed due to COVID-19, but we’re still building our new exhibit and bringing you educational content.

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