The March Brown Mayfly adult is short-lived, but its very presence is a sign that the water is clean and the fish will be biting.
Mayflies are generally a good indicator of water quality. The early part of a Mayfly's life is under water, and they do not thrive in polluted streams, creeks, or other aquatic habitats. March Brown Mayflies are a popular food source for fish, especially trout, so anglers are keen to recognize them by appearance, behavior, and life stage. Such knowledge increases one's likelihood of catching fish by using a fishing lure that matches the present species of Mayfly.
Four general life stages are present in the March Brown: egg, nymph, subimago, and imago. Huge swarms form, usually over water, which have occasionally caused a commotion in more developed areas where people are not used to seeing them. After briefly mating in the air, females lay fertilized eggs at the water's surface. The newly hatched nymphs resemble crustaceans with large jaws. They search out slower-moving waters and feed for over a year until they crawl on land to molt into a more familiar winged Mayfly form. The early winged form of Mayfly is called a subimago by biologists, and a dun to anglers, and it is not able reproduce yet. Another molt produces the sexually mature adult, called an imago by biologists, and a spinner to anglers. A spinner gets its name from the circular swimming motion that results from flapping its wings on the water's surface. After laying eggs, females die and their bodies, almost transparent in water, float on the surface. Fish love eating Mayflies, and are very active during a spinner fall, when the Mayflies drop dead after reproducing. A swarm is an indication that some good fishing may be coming soon to that area.
March Browns and Gray Foxes were once considered separate species, and even differ a little in appearance, but they are now known to be the same. The Gray Fox form seems to develop after the March Brown form. Both forms are great for fishing. Though the adult lifespan of the March Brown Mayfly is short (a day), the presence of adults and swarms can last for a week as fully grown nymphs leave the water to molt.
Scientific Name: Maccaffertium vicarium
Other Name(s): March Brown Dun, Gray Fox Dun, March Brown Spinner, American March Brown,
Size (Adult; Length): 9mm to 16mm (0.35in to 0.62in)
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