The Niobrara Valley Preserve’s Hybrid Butterflies

There are three members of the genus Limenitis found in Nebraska. They are Red-spotted Purple (L. arthemis astyanax), Viceroy (L. archippus) and Weidemeyer’s Admiral (L. weiedemeyeri). When we first began surveying butterflies at the Niobrara Valley Preserve in Brown, Keya Paha and Cherry counties back in 1986 we found all three to be present there. The first two were common while Weidemeyer’s Admiral sightings were rare.

Billed as a biological crossroads the Preserve proved to be just that for these three species. The Weidemeyer’s Admiral was at the easternmost extension of its range while the Red-spotted Purple was at its westernmost. Viceroys and Red-spotted Purples are still common at the Preserve but Weidemeyer’s Admirals have not been found there since 1995.

In the years between 1986 to 1995 we found evidence that these three butterflies were hybridizing. We found four individuals that appeared to be the result of crosses between Red-Spotted Purples and Weidemeyer’s Admirals and one individual from a Viceroy x Weidemeyer’s Admiral pairing.

Weidemeyer Admiral x Red-spotted Purple Hybrids

We found the Weidemeyer Admiral x Red-spotted Purple hybrids in late June/early July. This was consistent with the flight period of both species at the Preserve.

Viceroy x Weidemeyer’s Admiral Hybrid

Below is an image of a Viceroy and Weidemeyer’s Admiral and the one hybrid of those two species that we found. Interestingly this hybrid seemed to develop as a Viceroy as it was found in August when a second brood Viceroys can be found. At the Preserve both the Weidemeyer’s Admiral and Red-spotted Purple fly in a single brood in June and July.

More questions than answers

There are a lot of questions as a result of these findings. 1) Why are the Weidemeyer’s Admirals no longer there? 2) How long had they been there prior to 1986? 3) Where is the new eastern edge of their range and is hybridization still occurring there?

The answer to the first question – why they are no longer there – is puzzling. The hostplant chokecherry is still present, so it must be an environmental factor. Heat? Humidity? Pathogens? Parasites/Predators? A combination of these and some other unknown factor? We do not always understand what limits where a species can live, and conditions in nature are always changing. That means the range boundaries are fluid. Food for thought/research!

As for the second question, how long had Weidemeyer’s Admirals been at the Preserve before 1986? I wish I knew. That is the value of citizen science and why individual projects like this over time can provide valuable information. At this point all we can do is continue to observe.

Lastly, I would expect that hybridization is still occurring at the eastern edge of the Weidemeyer’s Admirals range with one or both of its sibling species whether that be in Cherry county or somewhere farther west. However, at this time we do not know precisely where that range is overlapping.

It is interesting to ponder and exactly the reason we do what we do.

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