- Ephemera danica, commonly known as the green drake mayfly, is one of the most widespread and recognizable mayfly species in Europe. Belonging to the order Ephemeroptera and the family Ephemeridae, this species is renowned for its delicate beauty, short adult lifespan, and ecological importance in freshwater ecosystems. It is commonly found throughout Europe and parts of western Asia, inhabiting clean, well-oxygenated rivers and streams with sandy or gravelly bottoms. E. danica is a quintessential representative of mayflies, an ancient group of insects that have existed for over 300 million years, making them one of the most primitive lineages of winged insects still alive today.
- Adult Ephemera danica are slender, fragile insects, typically measuring 15 to 20 millimeters in body length, with an additional 25 to 30 millimeters of long, filamentous caudal cerci (tails) extending from the abdomen. Their two pairs of membranous wings are large, transparent, and held upright when at rest—similar to butterflies. The forewings are much larger than the hindwings and have an intricate network of veins. Adults are pale yellowish to greenish with brown or gray markings, and they possess large compound eyes and short antennae. The mouthparts are vestigial, meaning adults do not feed; their sole purpose is reproduction. This stage of the insect’s life is fleeting—lasting only a few days or even hours, which gives rise to the order’s name, Ephemeroptera (“short-lived wing”).
- The life cycle of E. danica demonstrates incomplete metamorphosis, comprising three stages: egg, nymph (naiad), and adult—a process that includes a unique subimago stage found only in mayflies. Females lay their eggs on the surface of the water, from where they sink and adhere to the substrate, often among sand or gravel. The nymphs, or aquatic larvae, hatch after several weeks and live underwater for one to two years, depending on environmental conditions. These nymphs are burrowing forms, adapted to digging U-shaped tunnels in sandy riverbeds using their strong, spade-like forelegs. They respire through a series of plate-like gills located along the sides of the abdomen, which undulate rhythmically to aid gas exchange in flowing water.
- Nymphs of Ephemera danica feed on detritus and organic particles, playing an important role as decomposers in aquatic ecosystems. They consume fine sediments, decaying vegetation, and microorganisms, helping to recycle nutrients within freshwater environments. As they grow, they molt 20 to 30 times before reaching maturity. When environmental cues such as temperature and light conditions signal readiness, the nymph swims to the water surface, emerging as a subimago, or “dun,”—a winged but sexually immature stage. The subimago is duller in color, with opaque wings and a velvety body covering.
- After a short period (typically 24 to 48 hours), the subimago molts once more into the imago, or sexually mature adult. This final molt—unique among insects—marks the completion of development. Adults immediately seek mates in synchronized mass swarms, often occurring above rivers in late spring and early summer. Males perform a characteristic “dancing” flight to attract females, after which mating occurs mid-air. Females then deposit their eggs on the water’s surface before dying soon afterward. The entire adult lifespan of E. danica rarely exceeds a few days, emphasizing the ephemeral nature of this species’ existence.
- Ecologically, Ephemera danica is a key component of freshwater ecosystems. The nymphs are an essential part of aquatic food webs, serving as prey for fish (such as trout and grayling), amphibians, birds, and other invertebrates. Their sensitivity to pollution, oxygen depletion, and habitat disturbance makes them excellent bioindicators of water quality—their presence typically signifies clean, unpolluted freshwater environments. Adult mayflies also contribute briefly to terrestrial ecosystems, providing food for birds, bats, and spiders during their mass emergences.
- From a cultural and scientific perspective, Ephemera danica has long fascinated naturalists, anglers, and ecologists alike. Fly fishers value the species highly, as its emergence triggers one of the most anticipated “mayfly hatches” of the year, inspiring artificial fly patterns used in traditional angling. The synchronized swarming behavior and brief, delicate life of mayflies have also inspired poetic and philosophical reflections on ephemerality and the cycle of life.
