San Juan River Hatches and Flies

Mayflys

The most distinctive feature of the mayfly is its tail. Adult mayflies are a winged insect with two or three long, thin tails extending from the back of their abdomen. Their wings are partially transparent. Most mayflies are reddish brown, brown or slate gray, but some are lime green. Their bodies have a slightly flattened appearance because of the row of gills along the sides of their abdomen.

The pupa mayfly is most noticeable when it is resting on the surface of the water, waiting for its wings to dry after emerging from the lake. In this position, they appear very triangular in shape.

Mayflies swarm and mate in flight. The males bob up and down in the air - which is why they are sometimes called "dippers" - while the females fly straight through the swarm until seized by a dipping male. The female lays her eggs while skimming over the surface, or sometimes she will dive like a submarine and lay them in the bottom weeds. The eggs hatch into a larva or nymph which hides on the lake bottom, sometimes burrowing into the mud. Nymphs grow and then transform into a pupa form called a "sub-imago," which surfaces, dries, and then transforms into an adult.

Mayfly nymphs usually mature in about four weeks, but some species can take up to four years to become adults. Most mayfly species have no mouthparts and cannot feed, so they live a very short time, usually only a day or so. As they are very vulnerable to predation while their wings dry, they make up an important part of a fish's diet. Once they mate and die, they are often found floating on the rivers surface. These dead adults (or spinners) are also important fish food.

Midge

Chironomids (pronunciation: kira-no-mid) are probably best known as gnats. Their larvae are also called bloodworms or midges. They are the most important food source for trout on the San Juan River.

Adult chironomids look like mosquitoes with feathery antenna. Chironomid larva have segmented bodies, are worm-like and look much like a long skinny grub. Larva may be a variety of colors from cream to black, but they are very often bright red. The pupa are black, brown, reddish-brown or green but can come in many other colors. They are #30 to #18 in hook sizes.

Free swimming larva, like the bloodworm, do just that. They crawl, float or swim around the lake but generally tend to hide under rocks or rotting logs and remain fairly immobile. Chironimids will live pretty much anywhere that they can find food. They will live in both salt and fresh water and in clean or polluted water. There are many different species and sub species and it is believed that they live the world over

Midge Lifecycle

Most chironomids have a one-year life cycle. After the female lays her eggs on the surface of the lake the eggs sink and settle in the mud at the bottom of a lake. Once the larva of the midge hatches (this stage is also called a bloodworm), it will build itself a tube out of mud to live in. As the larva develops and grows it may molt up to six times (lose its outer skin, like a snake does).

Once it is a mature larva, the midge will seal up the tube and begin to change into a pupa. This change may take several weeks. After this transformation is complete, the pupa wiggles out of the tube and begins to rise to the surface of the lake. The upward voyage is helped by air trapped beneath the pupa's skin. The midge pupa wiggles its body upwards, keeping its head up and tail down. Once it reaches the surface, the pupa skin breaks open and the adult crawls onto the surface of the water. The process of breaking open the pupa skin, the adult crawling out, drying its wings and flying away usually takes less than a minute. The adult midge then flies off to mate. Adults swarm and mate in flight. The females return to lay eggs on the surface of the water and the life cycle is complete. Adult midges may live a few hours or up to two months before they mate. Once the female lays her eggs she dies.