Midges and Mayflies

May 13, 2010

by Steve Blight

Photo Top Right: Adult male midge -- males have feathery antennae. Bottom Right: Adult Mayfly.

Now that the wildflowers are out and the migratory birds have either arrived or are on their way home, there is something else to look forward to – bugs! Two of the most abundant kinds of insects that people are going to see (lots of) in the Land O’ Lakes region are midges and mayflies. Anybody who has ever spent time outdoors in our area will be familiar with these often superabundant insects.

Let’s start with midges. Midges are insects that vaguely resemble mosquitoes but don’t bite – which is fortunate, because there are so many of them. There are at least 700 species of midges in North America alone. Clouds of insects “dancing” in shafts of sunlight filtering down through the forest canopy or along a woodland road are very often midges. They are among the earliest insects seen in the spring, often seen flying above snow-laden landscapes on mild days in early spring. Watch for dragonflies zipping through the columns of midges, picking off preoccupied ones for a quick meal.

Midges form a family of insects known as Chironomidae (informally known as chironomids). Adult midges have several interesting names including "lake flies" "muckleheads", "muffleheads" or even "chizzywinks" in Florida. Midges generally breed in water through a four-stage life cycle – egg, larva, pupa and adult. The life cycle starts when eggs are released as the female dips the tip of her abdomen in the surface film while flying low over water. The eggs sink to the bottom and within two weeks hatch into larvae.

The larva is worm-like in appearance and lives in the bottom of water bodies, spending most of its time intercepting drifting food. Chironomid larvae are often referred to as "bloodworms" because of their blood red colouration. This colouration is a result of living in poorly oxygenated water typically associated with deeper waters.

Once the larva is fully developed, it will seal itself in its tube and transform into the pupal stage. It usually takes several weeks for the change to occur. The pupa then cuts its way out of the old larval tube and with the aid of trapped gases under the thorax and abdomen, rises slowly to the surface of the lake. This pupal ascent attracts the attention of hungry fish, including trout. When large numbers of midges rise at the same time, the phenomenon is known to fly fishermen as a “hatch”. Upon reaching the surface, a split forms along the back of the thorax and the adult midge crawls out and flies off. Mating occurs within a day of hatching and the cycle is completed.

Mayflies are active in late spring or early summer, often in prodigious numbers. When I was growing up on the shores of the St Lawrence River near Montreal, July 1 was known for two things – fireworks and great drifts of dead mayflies piled up against the curbs along the streets. We called mayflies “poppers” for the cracking sound they made when they were crushed by a bicycle tire – the unfortunate but unavoidable fate of many mayflies!

Mayflies are aquatic insects whose lifecycle consists of only three stages – egg, naiad (or nymph), and adult. The naiad stage normally takes place in freshwater and lasts about a year. Mayflies are unusual in that they molt one final time after acquiring functional wings. This stage is usually very short – often only hours – and is known to fly fishermen as a dun. Duns are a favourite food of many fish, and fishing flies are often modeled to resemble them.

Adult mayflies are short-lived, ranging from a few minutes to a few days depending on the species. With about 630 species in North America, mayflies are sensitive to pollution, meaning that if mayflies are in or around a water body, the water quality is likely good. Plus, along with midges, they are eaten in prodigious quantities by aerial-foraging birds such as swallows. What would spring and summer be in the Land O’ Lakes be without vast numbers of midges and mayflies? At least they don’t bite!

Please feel free to report any observations to Lorraine Julien at This email address is being protected from spambots. You need JavaScript enabled to view it.  or Steve Blight at This email address is being protected from spambots. You need JavaScript enabled to view it.