Do mayflies bite?


Are you curious about those swarms of insects buzzing around lakes and rivers and wondering whether or not they bite? Have you ever wondered why these insects are so prevalent around water bodies? Interestingly, mayflies, known for their dramatic and brief appearances, are some of the oldest insects on Earth, with a lineage dating back over 300 million years! 

Today, we're going to delve into the behaviors and ecological significance of these fascinating creatures. By the end of this article, you'll not only understand whether mayflies bite but also appreciate their impact on the environment and how they interact with us during their fleeting life above water.

What are mayflies and do they pose a threat?


Mayflies, also known as shad flies or fish flies, are among the most ancient insects, as noted above. They are especially known for their unique life cycle and ephemeral presence above water, which usually lasts for just a few hours to a couple of days. 

The question, however, remains: do mayflies bite? The answer is no. Mayflies do not have the mouthparts required for biting. Adult mayflies do not eat at all; their mouths are non-functional, and their primary purpose during their brief adult life is to reproduce.

Fact: Adult mayflies are equipped with vestigial mouthparts, which means they cannot bite or eat. Their energy is derived from the reserves accumulated during their larval stage in the water.

Before we delve deeper, do you know how mayflies can indicate the health of the water they inhabit? Let's find out how their life cycle offers clues about environmental conditions.

The ecological role of mayflies

Mayflies are often excellent indicators of water quality, spending most of their life cycle as nymphs submerged in river beds. Here, they undergo significant development, growing and molting about 20 times over two to three years before emerging as short-lived adults. This extensive developmental phase makes them particularly vulnerable to water pollution and marks them as crucial indicators of the ecological health of their habitats. Their presence and abundance provide valuable insights into environmental conditions.


Once they emerge, mayflies have a profound impact on local ecosystems:

  • Reproductive cycle: The life cycle of mayflies is incredibly brief but pivotal. After hatching, male mayflies quickly seize females to mate in midair. Following this aerial mating, the males die almost immediately. Each female then drops thousands of eggs into the river before she also meets her end. Did you know? Mayflies are one of the few creatures where the adult stage is devoted solely to reproduction. They are born, reproduce and die in less than 48 hours. This quick cycle is why you see such intense swarms!
  • Nutrient contribution: The eggs dropped into the water provide essential nutrients to aquatic environments, enhancing the growth of aquatic plants and benefiting water quality.
  • Food source for predators: Adult mayflies serve as a vital food source for a variety of predators, including fish and birds. Their massive emergences are crucial for feeding local wildlife, particularly during large swarms.
    Ecological significance:
    • Population health: A significant resurgence in mayfly populations along clean waterways signifies ecological recovery and health, while a decrease often indicates ecological downturns.
    • Case study:  Recent studies using advanced radar technology have documented a drastic decline of over 50% in mayfly populations along the Upper Mississippi River and Western Lake Erie Basin from 2012 to 2019. This research, published in the Proceedings of the National Academy of Sciences, highlights the critical ecological role of mayflies. Annually, mayflies provide about 12 trillion calories to the ecosystem, substantially supporting local food webs. The decline, driven by deteriorating water quality and warmer temperatures, underscores the vulnerability of these insects and signals broader environmental challenges. This alarming trend not only impacts local biodiversity but also serves as a warning about the health of our waterways and the potential onset of an 'insect apocalypse. Did you know? Research using radar technology has revealed that a single large swarm of mayflies can contain up to 88 billion individuals.
    prevent-mayflies-from-coming -inside-homes

    Dealing with mayfly swarms: Tips and strategies

    What should you do during a mayfly swarm? While mayflies are harmless since they don’t bite or sting, their swarms can sometimes be a nuisance, especially near bodies of water where they hatch in large numbers. During certain times of the year, these swarms are so dense that they can cover local roads and homes. 

    Strategies for managing these swarms include reducing outdoor lighting, which attracts them, and using barriers to prevent them from entering homes and other buildings.

    Conclusion: Embracing mayflies

    In summary, mayflies do not bite, nor do they pose any direct harm to humans. Instead, they play vital roles in aquatic ecosystems and act as indicators of environmental health. Their dramatic life cycle and the massive swarms are not just a natural spectacle but also a demonstration of nature's resilience and capacity for regeneration. So, rather than worrying about whether mayflies bite, we can appreciate the important role they play in signaling the health of our environment.

    At Dr. Killigan's, we are committed to respecting and preserving the natural world. By embracing the natural world with knowledge and understanding, we recognize the significant contributions even the smallest and most ephemeral creatures, like the mayfly, make to our planet's biodiversity. Explore more about how we support sustainable practices and help protect the environment by visiting our website. Join us in our mission to foster a harmonious coexistence with nature.

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