The Dope on Duskywings (Juvenal’s vs Horace’s)

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.

Note the two large pale spots near the leading edge of the ventral hindwing in this male Juvenal’s Duskywing.
These white hairlike scales scattered over the forewing of male Juvenal’s Duskywing differentiate it in hand (or with XCU macro shots) from Horace’s.

[No butterflies were harmed in this examination 😉]

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5 Responses to The Dope on Duskywings (Juvenal’s vs Horace’s)

  1. rob@snphotos.com says:

    Hi Harry and Rick

    We are working a lot in Shenandoah NP this spring doing revisions on both our SNP Wildflower Book and Nature guide to Shenandoah. We have been looking for Appalachian Swallowtails all spring and it was just Monday that we saw our first candidate at Graves Mill Trial on the east edge of the park at about 1000 feet elevation. If you guys agree the ratio was about 14 APSW to 2 ETSW. Also, we had 2 potential Appalachian azures, they looked large and wondered if you could see enough of the dorsal side to identify the one we got a picture of. Compared to what we have been seeing all spring, both and Ann and I immediately said that looks big. We did not see them go to Black Cohosh but there is of course lots available locally.

    In Shenandoah do we have other Azures beyond Spring, Summer (spring and summer types), Appalachian and Silvery Blue (we have only had one Brown Gap a few years ago where lots of Carolina Vetch grows).

    There is so much Goatsbeard I wonder if anyone has ever had Dusky Azure in the park – we have never seen it.

    Thanks to both of you for the hard work you do and for your willingness to keep us educated and informed.

    Best to you – Rob

    Ann and Rob Simpson

    http://www.agpix.com/snphotos

    http://www.AnnRobSimpson.com

    Simpson Nature Photography

    Natural History Travel Tours Round the World

    Authors and Photographers for Falcon Press

    Nature Guide Series of National Parks

    Wildflower Series of National Parks

    Authors and Photographers for Far Country Press

    Baby Animals Series and Children’s Nature Books

    Ann, Professor of Biology, Anatomy and Physiology

    Rob, Professor Emeritus Biology, Nature Photography (Program Contact)

    Rob 540 336 3003, Ann 540 336 2979

  2. Rick says:

    Hi Ann, Rob … Very much looking forward to the new editions! Harry would be better able to answer both questions, actually, but here in MD we don’t usually see Appalachian Tiger Swallowtails this early. They typically fly in the lull between Eastern Tiger flights, the first of which is still active. The same is true for us with Appalachian Azure, which for us in the Catoctins flies mid-May at the earliest to mid-June. Harry can also tell you the prospects for Northern Azure and Cherry Gall Azure, both of which I suspect would be candidates for SNP. I don’t know of any sightings of Dusky Azure in SNP, but I strongly suspect it is regularly overlooked as simply a dark azure. It is believed to have been extirpated in MD about a decade ago when the only known habitat for the butterfly was paved over.

  3. Rick says:

    Also, I’m afraid I can’t figure out which link takes me to the azure photo you were asking about …

  4. Harry Pavulaan says:

    Hi Rob:

    Thanks for looping me in. The Tigers are tough, as there seems to be a mix of Appalachian and Eastern. The one image with an individual in the forefront with wings closed is a large Eastern Tiger by the very narrow black edge to the abdominal margin of the hindwing. Others could be Appalachian but all candidates are backlit, making it hard to tell if the submarginal yellow spots on the underside forewing are fused into a band (making them candidates for Appy). I do see one in the underside image that looks good. But I do know that appalachiensis comes out in gangbusters at this time, on the road up from Sperryville.

    Yup, that Azure is certainly neglectamajor. Very common in Shenandoah National Park. Sometime (in the next week or two if I can get a free day), I’d be interested in going up to see the Goatsbeard. I know there is much of it alongside Skyline Drive but I have never found C. nigra caterpillars on it. Most likely place for nigra would be where Goatsbeard grows in deep, cool hollows. Forget trying to find adults in the forest, they are extremely elusive. When I lived in Missouri, I only ever saw one adult but the eggs and caterpillars were very easy to find on Goatsbeard but it’s tricky if you don’t know how to spot them. We could try to meet sometime or give me a good spot to inspect and I can very quickly tell if nigra is there (it would have to be an easy hike from Skyline Drive or up from the bottom, as I am having some health issues that limit my hiking uphill). I did find nigra in the Great Smokies back in 1988 – caterpillars up at around 5000’. A trip up there two years ago found no nigra and no Goatsbeard.

    Best, Harry

    Sent from Mail for Windows 10

  5. rob@snphotos.com says:

    Harry

    Thank you for all of the information. I had one huge group of swallowtails and when I tried to get into better front light they all swirled into the air. I knew the backlighting would make id difficult. Many in that group seemed to be very large like Appalachians and all were very fresh. I have emailed Mara Meisel for her records on Goatsbead locations (she has a great digital collection of observations). One area that has quite a bit is just south of Jenkins Gap along the west side of the road. I would say all of my sites are along the Skyline Drive so getting to them is not a problem. I grew up in Canada and my knees suffer from numerous hockey incidents – so I appreciate your mobility pain. As soon as I hear from Mara I will let you know – actually I will cc her on this. If we are available I would love to be able to see how you look for the eggs/larva of the Dusky Blue. I was one of Herb Wagner’s students and I thought he had told me he had found the Dusky in Shenandoah National Park. However unlike Mara’s detailed records my memory is not reliable from a conversation 45 years ago. As you probably know Herb passed away a few years ago.

    Can you tell me what to look for on the Appalachian Azure that would make it identifiable when you can see the dorsal side or do you need a microscope to look at the scales?

    Thanks again – Rob

    Ann and Rob Simpson

    http://www.agpix.com/snphotos

    http://www.AnnRobSimpson.com

    Simpson Nature Photography

    Natural History Travel Tours Round the World

    Authors and Photographers for Falcon Press

    Nature Guide Series of National Parks

    Wildflower Series of National Parks

    Authors and Photographers for Far Country Press

    Baby Animals Series and Children’s Nature Books

    Ann, Professor of Biology, Anatomy and Physiology

    Rob, Professor Emeritus Biology, Nature Photography (Program Contact)

    Rob 540 336 3003, Ann 540 336 2979

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