Updates from April 19, 2006

Dun: 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.

Instar: Many invertebrates molt through dozens of progressively larger and better-developed stages as they grow. Each of these stages is known as an instar. Hard-bodied nymphs typically molt through more instars than soft-bodied larvae.

Larva: Many classes of aquatic insects, such as caddisflies, midges, craneflies, dobsonflies, alderflies, and many more, are known as "larvae" rather than "nymphs" in their juvenile stages. They have mostly soft bodies rather than hard exoskeletons. These insects also advance through a "pupa" stage before reaching adulthood.

Molting: When aquatic insects with hard exoskeletons (like mayfly and stonefly nymphs) grow bigger, their exoskeleton does not grow with them. Instead they grow a new, larger one underneath and shed the old one when it's too small. This process is called molting.

Natural: A natural is a real insect (or similar creature) a trout might eat. The term is used to specify the real thing as opposed to its artificial imitation.

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).

Pupa: Any insect which spends most of its juvenile lifetime as a larva first becomes a pupa for a time before emerging as a fully grown adult. Depending on the species, the pupal form can be very important for fly fishermen to imitate.

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.

Spent: The wing position of many aquatic insects when they fall on the water after mating. The wings of both sides lay flat on the water. The word may be used to describe insects with their wings in that position, as well as the position itself.

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.

Stillborn: In fly fishing, a stillborn insect is one which got stuck in its nymphal or pupal shuck during emergence and floats helplessly on the surface instead of flying away. It is a specific class of cripple, although it is sometimes used interchangeably with that term.

Tubercles: Various peculiar little bumps or projections on an insect. Their character is important for the identification of many kinds of insects, such as the nymphs of Ephemerellidae mayflies.

Wing pads: A protrusion from the thorax of an insect nymph which holds the developing wings. Black wing pads usually indicate that the nymph is nearly ready to emerge into an adult.