red speckled dun

Red speckled dun is a common small minnow mayfly. It occurs throughout the United States and southern Canada, and north along the West Coast to Alaska.

The young (nymphs) are found in a number of aquatic habitats, including in still water in lakes and ponds, and in rapidly moving water in streams.

Red speckled dun is small for a mayfly (Order Ephemeroptera) but medium-sized for a small minnow mayfly (Family Baetidae). Adults are about ½″ (12 mm) in length not including the tail filaments (cerci). The body is elongated, slender, and very soft. The coloration is highly variable, from pale brown to glossy brownish black.

The antennae, though short and bristle-like, are very long for a mayfly. The mouth parts are small, poorly developed, and non-functional. The compound eyes on the female are on the sides of the head. On the male the compound eyes have additional large, turban-like parts that meet at the top of the head. These adaptations are said to allow the male, when in a swarm, to isolate females that are not yet paired with another male.

There are two very long, hair-like sensory appendages (cerci) at the tip of the abdomen. They may be as long or longer than the body.

The forewings are large and triangular, and they have many veins. They are held together above the body when at rest. The veins are white. The second terminal branch of the front (anterior) branch of the first fork of the media vein is designated as the M₂ vein. The M₂ vein is nearly straight. There is a dark brown or blackish-brown stripe along the leading edge (costal margin). The stripe is broad and deeply and irregularly eroded for most of its length, but it is narrow and straight near the wing tip. The remainder of the wing may be clear or mostly dark with clear borders along each cross vein. The hindwings are reduced to pads.

The third segment (femur) of each leg is mostly pale yellowish-brown, darker just near the tip. On the hind legs the last part of the leg (tarsus), corresponding to the foot, has 3 or 4 segments.

There are two subspecies of red speckled dun. The eastern subspecies Callibaetis ferrugineus ferrugineus occurs from the East Coast west to the Great Plains. The western subspecies Callibaetis ferrugineus hageni occurs from the West Coast east to the Great Plains.

Body length: ½″ (12 mm)

Small aquatic organisms, algae, and organic debris

Adults do not feed

Sources

29, 30, 82, 83.

Common

Callibaetis ferrugineus (red speckled dun)

Callibaetis ferrugineus, red speckled dun mayfly, near the seasonal pond, which was almost dry. Photographed at Barnes Prairie, Racine Co., WI on June 1, 2022.

Babette Kis
6/1/2022

Location: Barnes Prairie, Racine County, WI

Callibaetis ferrugineus, red speckled dun mayfly, near the seasonal pond, which was almost dry. Photographed at Barnes Prairie, Racine Co., WI on June 1, 2022.