Stonefly Life Cycle
Stoneflies demonstrate an incomplete lifecycle, because they don't undergo metamorphosis.
1. Egg matures into a nymph.
2. The nymph lives on the bottom growing in stages called instars* until it matures. Depending on species maturity takes from three months to three years.
3. As the nymph nears maturity it migrates to the edge of the stream.
4. The nymph crawls out of the water, and up into the streamside vegetation, usually at night. Males usually emerge prior to the females. Here in the streamside vegetation the final instar is completed as the stonefly sheds it's husk becoming an adult. The adult stoneflies life span varies from a day or two to a few weeks.
5. Adult Stoneflies mate either within the vegetation or on the ground.
6. Females fly out over the stream to deposit eggs.
7. Female Stoneflies drop their egg sack into the water either by dropping it from above the stream surface, dipping their abdomen into the water's surface, while flying above it, or crawling across it. Some species crawl down the bank and deposit their eggs under the water.
8. The eggs drop to the stream bottom.
This is a general description of a Stonefly's life cycle.
*As invertebrates grow they shed their exoskeleton numerous times these periods of growth are called instars.