Distinctively Colored Mayfly Nymphs

Distinctively Colored Mayfly Nymphs Collected From the Ogeechee River
By: Damon Mullis
Tricorythode nymph

Mayfly

Recently while processing invertebrate samples from the Ogeechee River, I spotted six exceptionally colored mayfly nymphs. They were very small (2-4mm in length) and had striking pink markings. Upon further inspection, I discovered that they were a species of mayfly within the Tricorythode genus. There are thirteen species of Tricorythodes in North America, with four species regularly occurring in our area. While insect biologists have discovered characteristics to distinguish between these species in their adult life stage, no one has done the tedious work of rearing them in a laboratory to reveal differences in the nymphs. As a result, we are unfortunately only able to identify these nymphs to the genus level.

Tricorythode nymphs are typically found in areas of flowing water in large streams and rivers. They prefer slow moving water that is slightly acidic, making the rivers and streams of the Coastal Plain of Georgia an ideal environment. They feed on the dead plant material and diatoms that are plentiful in this habitat. These rivers and streams are also pretty silty, so these little insects have evolved specially adapted gills. The first pair of gills are thickened and plate-like and do not function to obtain oxygen. They cover the functional gills and protect them from being covered with silt, which would prevent them from obtaining oxygen. To obtain dissolved oxygen, they raise the plate-like gills slightly and circulate water under them by waving the functional gills back and forth.