Pale Morning Dun or PMD
Introduction
This
hatch occurs in our area on the Yellowstone
River, Boulder
River, Madison
River, all of the Spring
Creeks and many other streams during
the Middle of June and through July. Hatches can be very localized
and heavy at time. This is a gentlemans Mayfly as it usually begins
emergence around 10 in the morning and the dry flies, or Duns, can
last until about 3 in the afternoon.
Entomologists are always reclassifying species; most recently these species of PMDs. Ephemerella inermis is now E. excrucians and E. infrequens is now reclassified as a subspecies of Ephemerella dorothea. What does that mean to us anglers? Not much they still hatch, trout still eat them, and we can still call them Pale Morning Duns or PMDs.
Nymph Stage
All mayflies have an incomplete life cycle meaning there are only three stages of development egg, nymph and adult. In the nymph stage the may fiies live for up to a year developing underneath the waters surface. As nymphs they feed on algae, plankton and drifting detritus. They range in size up to about a #12 to #20 hook and are best imitated with Pheasant Tails, Sawyer Nymphs and other dark bodied nymph patterns.
Emergence to Adult
As the time of emergence draws closer the nymphs begin to rise up from the rocks underneath the waters surface. This occurs as a gas bubble forms inside the exoskeletion of the nymph. Turning over a few rocks along the banks will reveal numerous insects underneath with dark wing cases. Fishing a slightly weighted PMD emerger (size #14 to #18) can produce some excellent fish as they are extremely vulneralbe in this stage. Splashy rises often indicate trout taking this emerging mayfly.
Adults & Egg Layers
Adult
mayflies (size #14 to #20) have very short life spans as adults most
rarely live more than 24 hours. Right after emergence they float
on the surface of the water drying out their wings. They are easlily
identified by their upright wings which resemble a sailboat mast.
During more humid days this may take several hundred yards before
they are dry enought to fly off the surface of the water. Looking
in the tail outs of long runs often reveals trout eating these dry
flies or Duns. After the Duns leave the waters surface the molt to
a spinner stage identified by their now clear wings (with some slight
dark banding in this species). They then mate and lay their eggs
above the surface of the water. Most times they are so exhausted
they fall to the water and again are an easy meal for trout. These
are well imitated with a Harrop Last Chance Cripple or Hi-Vis
Parachute PMDin size #14 in fast water or down to #20 in slower moving
tailouts.
Spinners
After they have laid eggs the adults wings are clear and lay flat on the waters surface. Anglers often call this stage a spinner or a spent mayfly. Trout can become highly selective at this stage and careful observation will reveal if they are taking duns or spinners. So keep vigilant as different trout might be taking different stages of the insect even if they are in the same area of water. Often times this will happen in the evening or the next morning especially if there is no dew or strong winds.