Mayfly Dun to Spinner Illustrated

Most fly anglers know that mayflies have two adult stages: duns and spinners. Entomologists call them subimagos and imagos. See the main Ephemeroptera page for the basics of these two stages.

Much of angling literature and this website consists of tips about matching one stage or the other for the various species. In May of 2005 I caught one mayfly molting between the two stages.

It belongs to the species Leptophlebia cupida, which anglers know as the Black Quill.

The Dun

The Molting Process

The skin of the dun splits above the thorax (Thorax: The thorax is the middle part of an insect's body, in between the abdomen and the head, and to which the legs and wings are attached.) and it anchors its tarsi (

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

Tarsus: The often multi-segmented outer leg section of an insect, which attached to the tibia.) to the surface it's resting on. The entire spinner wriggles out forward through the opening in the thorax (Thorax: The thorax is the middle part of an insect's body, in between the abdomen and the head, and to which the legs and wings are attached.).

The Spinner

Readers who enjoy this sequence will also enjoy the shots of an Ephemera varia dun molting into a spinner in Ted Fauceglia's book Mayflies . His photos present the same process in a much more artistic manner.