Mayfly Nymphs

• Phylulm Arthropoda ("Jointed-Legs")
• Class Insecta ("Cut-Sections")
• Order Ephemeroptera ( "Short-Lived Wings")

Nymph Appearance Body types are designed for burrowing, swimming or creeping The body is torpedo-shaped for species that crawl Body is flattened for species clinging under rocks The body of some species appears to be armour-plated Most have three, hair-like tails Plate-like or feathery gills beat along the sides of the abdomen Each leg ends in just one claw

Nymph Behavior

• Swim by quickly wriggling the body up and down like the dolphin kick
• Most species moult 15-25 times while growing to full size

Nymph Feeding Types

• Mainly herbivorous on algae and detritus
• Scrapers have a flattened body and remove algae from rocks
• Filtering collectors have hairs on the front legs
• Gathering collectors have a no hairs on the front legs and feed on leaves

Adult Appearance A mass "hatch" of these delicate flying insects is an amazing natural event Slender, up-curving bodies Two or three long tails One pair of large, obvious wings is held upright and together when at rest Unique in having two adult stages First stage adults (duns) tend to have dull, dark, mottled, opaque wings Second stage adults (spinners) have light, translucent wings Some large, white specimens can fill the evening air like falling snowflakes Adults do not feed Short-lived (ephemeral) adult stage Live hours or days Different species are sometimes only identifiable by their genitalia! The art of "tying" immitation mayflies is the basis of trout fishing

Aquatic Habitat

• Live in all types of running water - fast or slow

Reproduction

• Life cycle includes egg, nymph and two adult stages
• Nymphs spend two years or more in a river
• Nymphs swim to the surface to emerge with wings
• Water temperature and photoperiod (daylight) is a stimulus to time the mass "hatch" of adults
• Mass emergences (hatching into adults) are "mayfly singles nights"
• Large clouds of insects make it easier to find mates in limited time
• The first adult stage "dun" quickly sheds to become a second stage "spinner"
• Adults live only a day or two and do not feed
• Adults are focussed purely on finding a mate before dying
• After mating and dropping eggs, adults die on the water surface
• The bodies of dead adults lie on the water with wings splayed apart ("spent spinners")

Predation

• Adult mayflies are the favoured food of trout
• Trout may eat the nymphs, rising nymphs, emergers, duns or spinners
• Trout feeding at the surface (rising) leave a ring of ripples or a splash
• Birds (gulls, waxwings) hover to feed on a hatch of mayflies
• Nymphs (wet flies) and adults (dry flies) are "tied" and used in fly-fishing

Nymph Pollution Tolerance

• Pollution sensitive
• Large numbers may indicate good water quality and high oxygen levels