Larva .
. . The larval stage occurs beneath the water's surface in all aquatic insects. It follows
the egg stage and is then followed by either the pupa stage or a
transitional stage that immediately precedes the adult.
For insects with an incomplete
metamorphosis, the term "nymph" is most often used by fly
fishers to refer to this stage. "Naiad" is the more
"scientific" term also
sometimes used.
caddis larva
Pupa
. . . The pupal stage is a transitional stage that occurs in more
advanced groups of insects; i.e., those with "complete"
metamorphosis. It is primarily a maturation stage, takes place
under water, and may be an active or inactive form. It may be either
free-living or encased.
The pupa stage is primarily of
significance to both fish and fishermen in areas where caddis flies are
prevalent. Mayflies and stoneflies do not have this stage.
caddis pupa
Subimago .
. . The subimago stage is a transitional stage unique to Mayflies (the order
ephemeroptera.) It follows the larval stage and precedes the adult
stage. Unlike other pre-adult stages in other insects, it is a
fully-winged, above-water form. (To
view an video clip of a subimago "hatching" from the nymphal
form, click here.)
Insects in this stage are often referred to as "duns."
They are differentiated from the final adult stage (called "imagos"
or "spinners") primarily by their darker,
"smoky-colored" wings.
mayfly subimago (dun)
Adult . . . The adult stage is the final, mature,
fully winged form of the life cycle. This stage takes place
above the water's surface.
Insects in the last stage become
fully developed, winged insects that are ready to fulfill their mating
requirements.
