Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
In 203 records from GBIF, adults of this genus have mostly been collected during May (34%), April (26%), June (17%), and March (12%).
In 587 records from GBIF, this genus has been collected at elevations ranging from 7 to 11601 ft, with an average (median) of 1165 ft.
Time of day: Evenings in the East, mid-mornings in the West (with exceptions)
Habitat: Riffles if available, otherwise specific locations based on several considerations.
It's been my suspicion for quite some time that a good part of the credit given to dorothea for creating the later, lighter-colored "little sulphur" hatch should probably go to the same species (or species complex) that creates the earlier, larger, darker hatch--E. invaria. Many anglers who fish the small suphurs on valley limestone streams in my home state believe (or have been led to believe) that they are fishing the dorothea hatch. Close inspection of the mayfly that causes the activity usually doesn't bear that out. Most of the true dorothea hatches seem to come from mountainous areas where the streams are faster and have rockier bottoms.
All of the specimens in this section are from PA, and this seems to provide a good case in point. This specimen and the nymph (#766) are good examples of dorothea, and they both came from sections of the Brodheads in the Poconos. The other specimens came from big limestoners and appear to be invaria. Notice that all of the dun and spinner specimens, except for this one, have banded tails (dark markings at the segments). As far as I know, this is not characteristic of the Eastern version of dorothea (E. dorothea dorothea), but it is a trait of invaria.