We’ve seen a lot of interest the last couple of days about how to tell apart our two common, large spreadwing skippers. By this, I mean the two named for Roman poets: Juvenal’s and Horace’s Duskywings, Erynnis juvenalis and Erynnis horatius, both of which are flying in April and May. We get a lot of pictures of these two, dark, quarter-sized skippers every year about this time. Both feed as caterpillars on oak, both nectar as adults on spring blossoms (blueberry, dandelion, cresses), and both look to the normal eye almost identical from above.
They both have a “bracelet” of 3 large white spots on their forewing “wrists” — this bracelet differentiates them from their cousins Dreamy and Sleepy Duskywings. They also both have another prominent white spot (the “costal spot”) about halfway between the “bracelet” and the base of the forewing, which distinguishes them from the otherwise similar Wild Indigo Duskywing. And they’re both rather strongly patterned in gray, brown, and black above, darker in males than in females. And for most of us, impossible to separate based on dorsal views alone. Pictures of just the upperside don’t help us get too far toward an ID.
Underneath, it’s a different story. Juvenal’s (male and female) have two large pale spots on the underside of the hindwing; these two large spots are absent on Horace’s. Problem is, neither duskywing usually shows its underside — you have to watch for a split-second when they raise their wings (very seldom; this is what gives this group the name spread-wing skippers), or see them balancing on a tall flower and showing their undersides as they move around the blossom.
Or net them and examine them in hand. If you do the latter, you’ll notice one other diagnostic character that separates the males — Juvenal’s Duskywings have long, white hair-like scales scattered over the forewings that Horace’s lacks. After the end of May or so, the situation is much clearer — Juvenal’s has only one brood a year, in the spring, while Horace’s flies again in midsummer.
[No butterflies were harmed in this examination ]