4 minute read
Solid Sulphers
Solid Sulphurs
In Michigan, the month of May features morels and mayflies. Finding morels requires hours of skilled hunting with a keen eye and a good dose of luck. On the other hand, finding mayflies is simple as they abound in our rivers during May. One of the most pleasant and longlasting hatches is the Big Sulphur Mayfly, Ephemerella invaria. Big Sulphurs, also sometimes referred to as Light Hendricksons, begin emerging in mid-May on the heels of the hallowed Hendricksons, Ephemerella subvaria, our opening day hatch. Sulphurs hatch steadily into early June before the smaller cousin, Ephemerella dorothea subsp. dorothea begin their aerial entrance. Whew, that’s a lot of Latin! Let’s translate into lay terms that can be used on the river.
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All of the mayflies in the Ephemerella genus share some similarities. First, the nymphs fall into the “spiny crawler” group, possessing shortened legs, spines and tubercles on the abdomen, and plate-like gills. They inhabit gravelly substrate, crawling around and feeding on bits of detritus as they grow and develop over a single year. Sulphur nymphs are unusual in that they have two color morphs, one completely dark brown and the other more pale and yellowish-brown (see photo above). I have raised the nymphs and separated the color morphs to determine if there are any notable distinctions in the adult stage—there are not. For the bug aficionados, Sulphur nymphs have a single, wholly pale segment (#6) on the top of their abdomens, making it quick to distinguish from its Hendrickson relative, which has three pale segments (#5,6,7) on top of their abdomens.
Mayflies in the Ephemerella genus have three caudal filaments or tails as adults. Tails are pale in Ephemerella invaria, subtly banded, with a touch of brown in the articulations of the tails. Another feature of the Ephemerella group is sexual dimorphism, and males and females in these species look somewhat different, not unlike some birds, such as our Northern Cardinal. The bodies of Ephemerella invaria male duns are brownish on the dorsal or top side and yellow on the bottom. Females are yellow on both sides. Colors are more intense in the spinner stage, and the fecund females can often be seen flying with a yellow egg sac protruding from their abdomens.
Eyes in all mayflies are large in males and much smaller in females. The compound eye of the male Ephemerella is red to reddish-orange on the top and brownish below. Additionally, E. invaria males have nearly contiguous eyes (i.e., touching) when viewed above or when looking at them head-on. The eyes of the female E. invaria are small
by Ann R. Miller
and yellow.
The wings in this mayfly genus are plain, without any heavy cross veining, as seen in Brown Drakes. Sulphur duns have pale gray wings when they emerge, which become completely hyaline or clear in the spinner or reproductive stage. A handy summary of the Ephemerella complex is this: nymphs in gravelly habitat, adults with three tails, plain wings, and sexual dimorphism.
It’s fascinating to review the older scientific literature regarding Ephemerella invaria. In recent years much of the mayfly taxonomy has been reviewed and updated. Not long ago, another mayfly also appeared in our May hatch charts, namely Ephemerella rotunda. Early taxonomists split this species out based on bumps (tubercles) along the rear abdomen in the nymph; adults were purportedly bigger than invaria and hatched 7-10 days sooner. Pouring over old descriptions detailed minute color differences between the two closely-related species. Eventually, taxonomists agreed that the two should become one species. More recent studies have shown that there is a degree of plasticity in mayfly development and that individuals that hatch earlier in the season can be slightly larger than later hatchers, possibly due to diminished resources as the season progresses.
Because Sulphurs are abundant and widely distributed, they are a joy to fish. Hatches begin in mid to late afternoon and happily can go on for some time. Spinners return to the river at dusk and again provide steady angling as females lay their eggs and males fall exhausted to the water. Yellow parachute or sparkle dun emergers in sizes 12-14 work well for hatches. As the season progresses, the mayflies get smaller, so carry a few size 16s as well. The smaller E. dorothea Sulphur does overlap as the season progresses, so be ready with size 18s in early to middle June. Understanding a little more about E. invaria will not only make you a better angler in Michigan but also in western states where the related Pale Morning Duns thrive, living in similar gravelly habits and behaving like our familiar Sulphur mayflies.
