Guest Post: An Emergence of March Flies

This spring and early summer this year, all across Newfoundland, we experienced a remarkable emergence of March flies (Bibio sp.). Swarms of flies seemed to be everywhere, which led to dozens of posts, newspaper articles, and radio interviews complaining about the inconvenient flies and asking how to destroy them. Some people convinced themselves that they had been stung or bitten by these harmless flies, others were concerned about the safety of their children, their pets, or their car’s paint job. Almost nobody was looking at what the flies were actually doing.

March Fly (Bibio sp.)
Photo by Michael Burzynski

In their juvenile stage most of us are unaware of these flies. Their larvae (unromantically called maggots) crawl through moist soil and feed on decaying organic matter and small roots. Once full grown, they turn into a pupa, and after a short while they emerge from the soil as a fully developed flying adult. Their emergence is coordinated so that the short-lived adults will all appear at roughly the same time and be able to mate. Males swarm in the air waiting for females to emerge from the soil. Once they have mated and laid eggs, their life is over.

These flies appear in huge numbers on occasion. They do not bite or sting, and in fact in western Newfoundland, if we get any apples, plums, or cherries on our trees this year it may be almost entirely because of the presence of these helpful flies. For several years now, cool springs have meant that the usual pollinators—assorted bees, beetles, and flies—are either still hibernating or are too chilled to fly, so there has been little or no pollination of early-flowering fruit trees in the Bonne Bay area—and almost no fruit grew on the trees.

This year, until it warmed up after mid-June, the only pollinators that I saw on our massively flowering cherry and apple trees were two bumblebees, a small flock of Cedar waxwings, and a swarm of March flies. The March flies were gorging on nectar, and in the process they were becoming sprinkled with pollen. A few weeks later, fruit were swelling on the cherry trees, showing that the March flies had done a great job of pollinating the flowers. Meanwhile, insect-eating birds were gorging on the flies as nesting season began.

Fertilized sweet cherries developing on the tree.
Photo by Michael Burzynski

In other parts of the Island, windrows of dead flies piled up on lakeshores and along sheltered bays, sparking concerns about what killed them. But this was a natural mortality caused by the weak flying ability of these insects. The flies swarm for mating, but if they get blown out over water they can only stay in the air for a relatively short time. As they land on the water, they drown, and the accumulating floating bodies are drifted in the same direction by the wind, until they reach shore. Because of the huge numbers of these flies this spring, and the large surface area of some of our water bodies, thick piles of dead flies formed wracklines along windward beaches.

Although they may not be the most attractive of our native insects, these flies are an important part of our natural ecosystems, both as larvae and as adults. When the mature adults emerge from the ground, they live only about a week, and are mainly interested in mating and laying eggs to start the new generation.

March fly feeding on nectar in cherry blossom.
Photo by Michael Burzynski

It would be great if the media could turn down the hyperbole when talking about natural organisms and events, avoiding comments such as “skin crawling”, “like a horror film”, “invasion”, and other terms that disgust people rather than intriguing them. Irruptions (sudden increases in population size) of March flies, Spruce Budworm moths, Hemlock Looper moths, and many other species are a normal part of the natural ecosystems around us. It is important to observe and appreciate these events, and the changes that they bring. It's time to stop complaining about March flies (sometimes called Lovebugs), and to learn to love them!

About the Author

Michael Burzynski was born in England and came to Canada when he was ten. Over the years he has lived in northern Québec, New Brunswick, and Nova Scotia, and moved to Rocky Harbour NL with his wife Anne in 1989. They both worked with Parks Canada until retiring in 2012. Michael is a naturalist, photographer, and writer.