**Mayfly Species Drunella cornutella (Small Blue-Winged Olive)**

Mayflies

Caddisflies

Stoneflies

Taxonomic Navigation -?-

Kingdom Animalia (Animals)

» Phylum Arthropoda (Arthropods)

» Class Insecta (Insects)

» Order Ephemeroptera (Mayflies)

» Family Ephemerellidae (Hendricksons, Sulphurs, PMDs, BWOs)

» Genus Drunella (Blue-Winged Olives)

» Species cornutella (Small Blue-Winged Olive)

Common Names

Match	Common Name
	Small Blue-Winged Olive
	Blue-Winged Olive

Few anglers can claim to have fished to hatches of this little olive mayfly, even though the species has been mentioned in popular angling entomologies like Caucci and Nastasi's Hatches or Knopp and Cormier's Mayflies. On many of the larger Eastern freestones, their emergence happens after the waters have warmed and dedicated anglers have turned their attention to streams that remain cold: headwaters, spring creeks, or tailwaters. Because good populations are usually not found in tiny streams, it is on some the Eastern tailwaters, like the branches of the Delaware, that fly fishers take notice of this species.

Drunella cornutella looks like a Mini-Me version of Drunella cornuta. In streams where the two species cohabit, size is the only easy way to tell them apart. Although there is some slight overlap between the largest cornutella and the smallest cornuta, the average difference is usually pretty obvious. Both share very similar coloration and morphology (Morphology: The form and structure of an organism, or the study of the form and structure of organisms.) in all stages, even down to the little curved horns coming out of the frontal shelves of the nymph's heads.

Where & When

Regions: East, Midwest

Time Of Year (?): Late June through August, sometimes into September on cold tailwaters

Preferred Waters: Relatively fast riffles and runs

They usually follow cornuta by about 3-4 weeks, often when water temperatures approach their seasonal peak.

Hatching Behavior

Time Of Day (?): Usually early morning, though tailwater timing can differ

Habitat: Similar to cornuta, though not extending as far upstream

Water Temperature: Emergence often commences as temperature approaches about 60-62 degrees.

On freestone streams, emergence often happens in the hour or so after dawn. On tailwaters with cold (hypolimnetic) releases in the summer, emergence can sometimes shift to the evening.

Spinner Behavior

Time Of Day: Evenings

Habitat: Riffled areas

Like cornuta, the spinners are usually not very important. On larger, warmer freestones, the spinner fall is a dusk-into-dark affair, and fish may not feed until the water cools. On tailwaters, the spinners may compete with larger or more numerous species.

Juvenile Biology

Current Speed: Fast to moderate

Substrate: Rocks and gravel

The nymphs are virtually identical to Drunella cornuta, but smaller (6-8 mm at maturity). Slight differences in tibia (

The tibia of this Isonychia bicolor mayfly spinner is highlighted in red.

Tibia: A middle segments in the leg of an insect, located between the femur and the tarsus.) length and other morphological niceties can be used to distinguish between cornutella and cornuta, but differences in size and emergence timing are more useful distinctions in the field. Range within a watershed also differs: cornutella tends to favor medium-to-large streams, and populations thin out in the headwaters; cornuta populations usually are found throughout the watershed, remaining strong into the headwaters.

Drunella cornutella Fly Fishing Tips

Larger "BWO" imitations used for Drunella cornuta need only be downsized, or "BWO" imitations used for Baetidae can upsized. Nymph imitations fish well during the period before or around emergence, even when opportunities to fish duns or spinners are slight.

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Jargon Defined:

Duns: Mayflies have two adult stages. They first emerge from the water as duns (scientifically known as the subimago stage). They then molt into the spinner (imago) stage, in which they mate and die. Sometimes the word "dun" is confusingly used to refer to a brownish gray color in fly tying materials.

Emergence: The transformation of a nymph or pupa into the adult winged stage of an insect. The term may refer to the emergence of an individual, or the daily or yearly event in which all individuals of a species emerge.

Morphology: The form and structure of an organism, or the study of the form and structure of organisms.

Nymph: The juvenile, underwater stages of mayflies, stoneflies, dragonflies, and damselflies and other aquatic insects whose juvenile stages are covered by hard exoskeletons. The word can also refer to the fishing flies which imitate these creatures, in which case it is used as a blanket term for flies imitating any underwater stage of an invertebrate (except for crayfish and leeches).

Spinner: There are two winged stages of adult mayflies. They emerge from the water as duns, molt on land (usually) into their fully mature stage, spinners. As spinners, they mate, lay eggs, and die.

The tibia of this Isonychia bicolor mayfly spinner is highlighted in red.

Tibia: A middle segments in the leg of an insect, located between the femur and the tarsus.