--- title: "Green Drake Mayfly (Ephemera danica) | AnimalTracks.wiki" description: "A burrowing mayfly that finds rivers by their polarized glint, and lands on smooth black plastic too." image: "https://animaltracks.wiki/images/animals/green-drake-mayfly-1.webp" published: "2026-10-11" updated: "2026-10-11" --- # Green Drake Mayfly (*Ephemera danica*) > **Status**: Checked against 7 sources, listed under Sources below. > **Tagline**: A burrowing mayfly that finds rivers by their polarized glint, and lands on smooth black plastic too. > **Soundtrack Vibe**: Post-Rock & Cinematic Orchestral // Sigur Rós, "Hoppípolla" > **Soundtrack Links**: [Spotify](https://open.spotify.com/track/6eTGxxQxiTFE6LfZHC33Wm) > **Vibe Match**: In the evening swarm, mainly males fly first, then a second phase arrives, mostly females, often carrying egg batches. Hoppípolla builds in waves too: piano and voice first, then strings and brass for the second rise. ## Biological Superpowers & Stats - **Taxonomy**: *Ephemera danica* - **Danger Level**: Low - **Conservation Status**: Not Evaluated ([IUCN Red List](https://www.iucnredlist.org/)) - **Superpower**: Detects water by the horizontal polarization of the light it reflects - **Habitat**: Sandy stretches of streams and rivers where the nymphs burrow, widespread throughout Europe - **Diet**: Nymphs filter or collect fine particulate organic detritus; adults do not feed - **Tags**: insect, freshwater, flying, burrower ## Natural History & Behavior ## Fooled by a smooth black surface Light reflected off water is horizontally polarized, which means its waves line up in one direction. *Ephemera danica* detects water with that signal. The more strongly a surface reflects horizontally polarized light, the more attractive it is to mayflies like this one. In a field test, smooth black plastic was the most attractive surface on offer. A cover textured like a rose petal was practically unattractive to them. On each test day, between 18:30 and 19:15, mainly males flew around the surfaces at first. Then, in the second phase of swarming, most of the landing mayflies were females, often with visible egg batches. Sometimes they laid those egg batches on the test surfaces. ## A burrower in the sand This is a large mayfly, 1.5 to 3.0 cm long, known both as the common mayfly and the green drake mayfly. Its nymphs, the young aquatic stage, live in the depositional zones of streams and rivers with a sandy bottom. There they construct a tubular burrow in the sediment and feed by filtering or collecting fine particulate organic detritus, which is tiny bits of dead material. The species is widespread throughout Europe, and emerging adults have been collected in the littoral zone of Lake Constance in Germany. The littoral zone is the shallow water near a lake's shore. Nymphs collected from a Devon river for lab tests weighed between 15 and 128 mg fresh. In two Polish rivers, small mayflies (optimal size 11.63 mm) were mainly settled by ciliated protozoans, and larger ones (optimal size 28.77 mm) by midge larvae. > **Passengers aboard** > On a single mayfly, researchers in two Polish rivers found between 0 and 18 midge larvae and from 0 to 46 ciliate colonies. ## A two-year cycle Across 2007 to 2013, *E. danica* at a cool, groundwater-fed reach of England's River Dove kept a 2-year emergence cycle. The adults then fly: the main flight period is towards the end of May, though adults are often present between April and November. As adults they do not feed, but they do use energy. In a study of the nymphs of this mayfly and another one, triglycerides, a type of fat, were the major energy reserve throughout development, at more than 84% of total energy storage in both. In male nymphs the triglyceride concentrations remained high until emergence, presumably because of the high energy demands of their swarming flights as adults. ## Frequently Asked Questions ### Does low oxygen matter to the green drake mayfly? Yes. In lab tests on the nymphs, hypoxia (low oxygen) lowered their lethal limits for warming by 5.5 °C. In UK stream samples, poor oxygenation drastically reduced how many sites they occupied, especially in warm water. *(Source: [Verberk et al. 2016]())* ### Can the green drake mayfly grow up in one year? Sometimes. On the River Dove in England's Peak District, after warm summers it emerged after only 1 year at the warmer upstream reach, then began to revert to a two-year cycle after the particularly wet, cool year of 2012. *(Source: [Everall et al. 2015]())* ### What is this mayfly's body built from? In emerging green drakes sampled at Lake Constance, terrestrial detritus (dead plant material from land) was the dominant nutrient source for the abdomen, head and wing, at 57%, 65% and 73% on average. *(Source: [Yohannes & Rothhaupt 2018]())* ## Sources 1. [Fritz et al. (2020). Bioreplicated coatings for photovoltaic solar panels nearly eliminate light pollution that harms polarotactic insects. PLOS ONE.]() 2. [Verberk et al. (2016). Field and laboratory studies reveal interacting effects of stream oxygenation and warming on aquatic ectotherms. Global Change Biology.]() 3. [Grzybkowska et al. (2016). Ephemera danica (Ephemeroptera: Ephemeridae) As a Resource for Two Commensals: Ciliated Protozoans (Sessilida) and Chironomids (Diptera). Journal of Insect Science.]() 4. [Everall et al. (2015). Detecting phenology change in the mayfly Ephemera danica: responses to spatial and temporal water temperature variations. Ecological Entomology.]() 5. [Yohannes & Rothhaupt (2018). Dietary nutrient allocation to somatic tissue synthesis in emerging subimago freshwater mayfly Ephemera danica. BMC Ecology.]() 6. [Winkelmann & Koop (2007). The management of metabolic energy storage during the life cycle of mayflies: a comparative field investigation of the collector-gatherer Ephemera danica and the scraper Rhithrogena semicolorata. Journal of Comparative Physiology B.]() 7. [Common mayfly. The Wildlife Trust of South and West Wales.]() *Published October 11, 2026. 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