**Mayfly Genus Baetis (Blue-Winged Olives)**

Mayflies

Caddisflies

Stoneflies

Taxonomic Navigation -?-

Kingdom Animalia (Animals)

» Phylum Arthropoda (Arthropods)

» Class Insecta (Insects)

» Order Ephemeroptera (Mayflies)

» Family Baetidae (Blue-Winged Olives)

» Genus Baetis (Blue-Winged Olives)

Species in Baetis
Baetis brunneicolorBlue-Winged Rusty Dun	0	0
Baetis flavistrigaDark Blue-Winged Olive	0	0
Baetis intercalarisBlue-Winged Olive	0	0
Baetis tricaudatusBlue-Winged Olive	2	15

18 species aren't included.

Common Names

Match	Common Name
	Blue-Winged Olives
	BWOs
	Rusty Spinners
	Little Brown Quills
	Little Blue-Winged Olives
	Little Iron Blue Quills

Fly Imitations by Orvis

Stage	Fly Pattern
Dun	Blue Winged Olive

Pictures Below ↓

This is one of the most prolific genera of mayflies in North American trout streams. Their small size permits the growth of up to three generations per year, and they are good dry-fly insects because they often hatch in impressive numbers and the duns ride the water for a long time before taking flight.

Baetis is probably the most misidentified genus in the angler's mayfly world. Many fly anglers see anything too small to imitate with a size 16 Adams and call it Baetis. In reality, Baetis is the most prominent of several very similar abundant genera in the family Baetidae. It seems every species in the family is perpetually being reclassified, and identifying any of them, even to genus level, is difficult.

The angler who wants to be accurate has two choices. Most people call these flies "Blue-Winged Olives," a name which has lost all meaning because people apply it to several dozen species which mostly have neither blue wings nor olive bodies. It's better to just call them "little (whatever color they are) mayflies." The other good choice is to call them "Baetids," the general Latin name for members of the Baetidae family, unless you've had them scrutinized under a microscope. Most of the specimens on this site can't be keyed below the family level from the pictures. So the next time a fishing buddy identifies a little greenish mayfly from a distance as Baetis vagans, just smile and nod...

Where & When

Some Baetis species are often the first major hatches in the Spring and the last in the Fall, and on especially stable spring creeks they may emerge throughout the Winter. The genus is common nationwide, but the East and Midwest have more of the really prolific species.

See each species page for more on their distribution and timing. Anglers searching for the infamous Baetis vagans can find it under its new name, Baetis tricaudatus.

Hatching Behavior

Time Of Day (?): Warmest part of the day during the cool season; sometimes sporadically all day long at other times
Water Temperature: 40°F and up

Baetis nymphs are normally outstanding swimmers, but they are reported to lose this ability when they emerge. They get to the surface by dead-drifting (Dead-drift: The manner in which a fly drifts on the water when not moving by itself or by the influence of a line. Trout often prefer dead-drifting prey and imitating the dead-drift in tricky currents is a major challenge of fly fishing.), buoyed by gas bubbles, or by crawling to the surface on some object and letting go to drift along in the film (rather than crawling out). They have trouble breaking through the surface film, escaping their shucks (

View Full Size

Here's an underwater view of the pupal shucks of several already-emerged Brachycentrus numerosus caddisflies.

Shuck: The shed exoskeleton left over when an insect molts into its next stage or instar. Most often it describes the last nymphal or pupal skin exited during emergence into a winged adult.), and drying their wings to take flight, which means that almost any type of surface fly has its uses. The Baetis angler may need to use deep nymphs, floating nymphs, emergers, cripple (Cripple: In fly fishing, a cripple is any insect which has been injured or deformed so that it cannot escape the water. This may include stillborn emergers or fully emerged adults which have been damaged, often by wind or waves, so that they can no longer fly. Trout often favor eating crippled insects.) patterns, or dun patterns during this emergence. Common wisdom says floating nymph and emerger patterns are the most useful.

Dismal weather invites the best hatches of Baetis mayflies; look for them on overcast, rainy days, as long as the water temperature is above 40°F.

Spinner Behavior

Timing the return of these mayflies as spinners after they hatch is difficult; some may come back within a few hours, while others take a few days.

Baetis females are among the only mayflies to lay their eggs underwater. The females land near the water after mating and crawl down to lay rows of eggs on the downstream side of rocks, sticks, and other objects. They may slip loose during the process or let go after they finish, and wet fly imitations are effective during this time. Ernest Schwiebert gives more detail in Matching the Hatch:

In moving through the surface film she folds her wings about her abdomen and uses the downstream side of the object she has selected. The passing through the surface film is the critical phase of her mating. Once she is under the surface, she inspects the rock or log carefully with her abdomen. Finally she lays her eggs with a circular sweeping motion, which leaves a little row of eggs each time. When her supply of eggs is exhausted she climbs back out of the water or is swept away in the underwater currents.

Nymph Biology

Baetis nymphs are found in almost every trout stream, but they produce more broods and thicker hatches in cold, unpolluted, alkaline (Alkaline: Having a pH higher than 7 (opposite of acidic). Moderately alkaline water is ideal for trout because it's better for the growth of phytoplankton, the usual base of the aquatic food chain, and that's good for the growth of everything higher up the chain, including trout.) waters. They inhabit almost every microhabitat in the stream except for silt beds, but gravel and vegetation are especially suitable.

Baetis Fly Fishing Tips

Because Baetis mayflies are so often called Blue-Winged Olives, some anglers try to imitate them with flies with blue wings and olive bodies. This is one of the follies of common names. Their wings are various shades of gray, maybe with a slight blue tint, and their bodies are various shades of olive or brown. When you meet a hatch, try to catch one of the live mayflies rather than assuming you know its color.

7 Mayfly Specimens in the Genus Baetis:

Specimen Page:12

Baetis (Blue-Winged Olives) Mayfly Dun

View 7 PicturesThis little early-season dun molted into this spinner after I photographed her.

Region: Catskills

Collected Apr 19, 2006

Added Apr 22, 2006

Baetis (Blue-Winged Olives) Mayfly Nymph

View 10 Pictures

Region: Catskills

Collected May 6, 2007

Added May 18, 2007

Baetis tricaudatus (Blue-Winged Olive) Mayfly Dun

View 7 PicturesThis female was associated with a male of the same species.

Region: Northeast

Collected Apr 3, 2007

Added Apr 4, 2007

Specimen Page:12

Recent Discussions of Baetis

Baetis flavistriga computatii 4 Replies »

Posted by CaseyP on Jan 22, 2007 in the species Baetis flavistriga

Last reply on Jan 23, 2007 by Troutnut

pleased to report the emergence of a new baetis flavistriga which i have christened computatii

forum visitors using the Firefox browser who put troutnut.com on their bookmarks toolbar have undoubtedly noticed a tiny dark mayfly icon in a blue box next the bookmark.

well, it's breeding. came back this evening from a week out of town to discover that the little troutnut computatii had a pal over next the hotmail.com bookmark where formerly there was only a generic white icon. am waiting for it to show up next the other two sites that have only generic icons.

now our resident boffins will help me with the Latin ending on the new name, (i tried to use the genitive plural) and then we'll ask Jason how he got these virtual flies to multiply.

Casey

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Jargon Defined:

Abdomen: The rear and usually the longest (ten-segmented in mayflies) portion of an insect's body, to which the tails are attached.

Alkaline: Having a pH higher than 7 (opposite of acidic). Moderately alkaline water is ideal for trout because it's better for the growth of phytoplankton, the usual base of the aquatic food chain, and that's good for the growth of everything higher up the chain, including trout.

Broods: When a species produces more than one generation per year, each one is called a brood.

Cripple: In fly fishing, a cripple is any insect which has been injured or deformed so that it cannot escape the water. This may include stillborn emergers or fully emerged adults which have been damaged, often by wind or waves, so that they can no longer fly. Trout often favor eating crippled insects.

Dead-drifting: The manner in which a fly drifts on the water when not moving by itself or by the influence of a line. Trout often prefer dead-drifting prey and imitating the dead-drift in tricky currents is a major challenge of fly fishing.

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.

Nymphs: 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).

View Full Size

Here's an underwater view of the pupal shucks of several already-emerged Brachycentrus numerosus caddisflies.

Shucks: The shed exoskeleton left over when an insect molts into its next stage or instar. Most often it describes the last nymphal or pupal skin exited during emergence into a winged adult.

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.

Useful References:

Caucci, Al and Nastasi, Bob. 2004. Hatches II. The Lyons Press.

Fauceglia, Ted. 2005. Mayflies . Stackpole Books.

Leonard, Justin W. and Fannie A. Leonard. 1962. Mayflies of Michigan Trout Streams. Cranbrook Institute of Science.

Schwiebert, Ernest G. 1955. Matching the Hatch. MacMillan Publishing Company.

Swisher, Doug and Carl Richards. 2000. Selective Trout. The Lyons Press.