The Mayfly & the Great Lakes

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If you live within a mile so of water, which is nearly everywhere in the Great Lakes region, you may notice the arrival of what many call “fish flies” during the late May, June and early July timeframe. While that nickname certainly applies to these insects, which can serve as a feast for many freshwater fish species, their proper name is the mayfly.

There are over 3,000 known species of mayflies worldwide, belonging to the order Ephemeroptera. These species vary in size, color, habitat preference, and lifecycle characteristics. Mayflies are found on every continent except Antarctica, and they inhabit a wide range of freshwater environments, including lakes, rivers, streams, and ponds.

But here in the Great Lakes, there is one species that “rises” above the rest. Hexagenia Limbata, also known as the Giant Burrowing Mayfly, is a species of mayfly that lives throughout most of North America.  And it is this species that we typically see near Great Lakes shorelines in late May, June and early July. 

IMPORTANCE TO LAKE ERIE AND THE LARGER GREAT LAKES FISHERY

Mayflies are an essential food source for many fish species in the Great Lakes. Fish such as perch, bass, walleye, and trout feed on mayflies at various stages of their lifecycle, including nymphs and adults (duns and spinners). Mayflies provide a high-energy food source rich in protein and fats, especially during their emergences when large numbers of them are available.

This mass emergence often triggers feeding frenzies among fish, leading to increased activity and successful angling. They play a significant role in the Great Lakes ecosystem by transferring energy from lower trophic levels to higher ones, ultimately supporting the fishery and contributing to the overall health of the ecosystem.

However, it’s essential to note that the health and dynamics of the Lake Erie fishery are influenced by a combination of factors, including water quality, nutrient levels, habitat availability, fishing pressure, and management practices. So while mayflies are certainly significant, they are just one piece of the complex puzzle that shapes the fishery in Lake Erie.

LIFECYCLE

The lifecycle of a mayfly typically consists of four stages: egg, nymph (or larvae), dun (subimago), and spinner (imago). Here’s a breakdown of each stage:

Egg

Mayflies lay their eggs in bodies of freshwater, such as lakes, rivers, or streams. The eggs are usually deposited on the surface of the water or on nearby vegetation. The time it takes for eggs to hatch varies depending on species and environmental conditions, but it generally ranges from a few days to several weeks.

Nymph

Once hatched, the mayfly larvae, also known as nymphs, live underwater. They undergo several molts as they grow, typically feeding on algae, detritus, and other organic matter found in the water. Mayfly nymphs can be found burrowing in sediment, clinging to rocks, or hiding among aquatic plants. This stage can last from a few months to several years, again depending on species and environmental factors.  Mayfly nymphs are often sold as bait in many Midwest baitshops.  Known as commonly as “wigglers”, they can be a very productive bait when used for the right species at the right time of year.

Subimago (Dun)

When the nymph is ready to emerge from the water and transform into an adult, it swims to the water’s surface or crawls onto emergent vegetation. Once at the surface, the nymph undergoes its final molt, shedding its aquatic skin and emerging as a subimago, commonly known as a dun. The dun has wings but is not yet fully mature. It rests on the surface of the water or nearby vegetation while its wings dry and harden.

Imago (Spinner)

After its wings have dried and hardened, the subimago flies to a nearby area, usually vegetation or land, where it completes its transformation into the fully mature adult, known as the imago or spinner. The adult mayfly typically has clear wings and a slender body. Its primary goal as an adult is to reproduce. Adult mayflies typically live only for a short period, ranging from a few hours to a few days, depending on the species. During this time, they mate, lay eggs, and then die, completing the lifecycle.

PROBLEMS

PROBLEMS

Mayflies typically do not present significant problems themselves. They don’t bite or sting. But their mass emergences can sometimes lead to nuisance issues or minor inconveniences. Here are a few potential problems associated with mayflies.

Swarming

During mass emergences, mayflies can form dense swarms near bodies of water, which may be considered a nuisance, especially in urban areas. These swarms can interfere with outdoor activities, such as picnics, recreational boating, or outdoor dining.

Messiness

After mating and laying eggs, adult mayflies often die en masse, leading to large numbers of dead insects accumulating on surfaces near water bodies. This can result in a messy cleanup, particularly if they accumulate in large numbers on roads, sidewalks, buildings, and vehicles.

Clogged Filters

In some cases, mayflies can clog intake screens and filters in industrial and municipal water treatment facilities, potentially causing operational issues and necessitating maintenance.

Power Outages

Massive swarms of mayflies have also caused power outages by bridging gaps to ground at power plant switchyards. This can cause damage to equipment as well as cost utilities their customers, hundreds of thousands to millions of dollars depending on the nature of the short.

CURRENT STATUS

Mayfly populations were nearly non-existed around 1960, but due to environmental cleanup efforts over the next several decades, they begin to rebound by the 1990’s. However, they have since begun a gradual decline in numbers which is still being analyzed to determine the cause. Some of the possible reasons for this follow.

Habitat Loss and Degradation

Changes in land use, urbanization, agricultural practices, and habitat destruction have resulted in the loss and degradation of freshwater habitats where mayflies live and breed. Pollution from agricultural runoff, urban stormwater runoff, industrial discharge, and habitat alteration can degrade water quality and reduce suitable habitat for mayflies.

Pollution

Mayflies are sensitive to water pollution, particularly to pollutants such as pesticides, fertilizers, heavy metals, and other contaminants. Pollution from various sources can directly harm mayfly populations by affecting their growth, development, and survival, as well as indirectly by reducing their food sources and disrupting aquatic ecosystems.

Climate Change

Climate change is altering environmental conditions, including temperature, precipitation patterns, and hydrological cycles, which can impact mayfly populations. Changes in temperature and water flow regimes can affect mayfly life cycles, emergence timing, and habitat availability. Additionally, climate change can exacerbate other stressors, such as habitat loss and pollution, further threatening mayflies.

Invasive Species

The introduction of non-native species, such as invasive aquatic plants, fish, and invertebrates, can disrupt native ecosystems and negatively impact mayfly populations. Invasive species can compete with mayflies for resources, prey on mayfly nymphs or adults, and alter habitat conditions, leading to declines in mayfly abundance and diversity.

Disease & Parasites

Mayflies are susceptible to diseases and parasitic infections, which can weaken individuals, reduce reproductive success, and contribute to population declines, especially in stressed or degraded habitats.

Addressing the decline of mayfly populations requires comprehensive efforts to mitigate habitat loss, reduce water pollution, mitigate the impacts of climate change, control invasive species, and implement sustainable management practices. Conservation measures aimed at protecting freshwater ecosystems and restoring degraded habitats can help support mayfly populations and promote their long-term viability.