Western March Brown
Introduction
This
hatch occurs in our area on the Yellowstone
River, Boulder
River, Madison
River and many other streams during April and May - particularly
when there are overcast skys or rain.
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 stream debris and drifting detritus. They range in size up to about a #10 or #12 hook and are best imitated with beadheaded Pheasant Tails or any bulky dark bodied nymph pattern.
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 Soft Hackle (size #12) 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 #12 or #14) 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 March Brown cripple or Hare's Ear Parachute in size #12 in fast water or a #14 in slower moving water.
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.