In my earlier post on the Spotted Bird Grasshopper I mentioned some interesting moth larva I found while hiking around the Sylvan Runkel State Preserve in the Loess Hills of Monona County last June. I took some photos, but couldn’t figure out what they were for quite a while. Finally, nearly three months later, they were identified as Hemileuca sp. through BugGuide.
Nevada Buck Moth, Sylvan Runkel State Preserve, Monona Co., IA, 18 Jun 2009.
After some additional research, I decided that they must be Nevada Buck Moth (Hemileuca nevadensis). This was based on range and a photo of a larva from Michigan. I contacted Dale Schweitzer, who wrote the buck moth accounts for NatureServe, and he confirmed the identification. This was exciting as it represented the first record for both the species and the genus for Iowa.
The timing of the identification was fortuitous, as the Nevada Buck Moth flight season in the upper Midwest begins in late-September and runs into October. I would still have a chance to go look for adults! Fortunately the moths are day fliers, so there would be no need for a nighttime expedition. On September 26, I headed back to preserve, hiked up to the top of the hill and within 15 minutes saw a buck moth. It blew past me, flying far faster than I expected, and I had no chance of catching it. A few minutes later, another flew by, then another, then another. Eventually, I was able to secure a few voucher specimens to make it official. That out of the way, I sat back and watched what was one of the coolest insect spectacles I have ever seen. The moths were flying everywhere. Often several males would tear off in the same direction, clearly following the pheromones of a female.
Male Nevada Buck Moth
Eventually I found a calling female and watched a dozen or so males come circling in, crashing through big bluestem, until one found her and they mated.
- Mating Nevada Buck Moths
As it got close to noon, the flight was pretty much over for the day. However, male moths were still perched randomly along the trail. When approached too closely, they assumed this defensive posture:
Male Nevada Buck Moth
The bright orange and white coloration, combined with the fact that these moths fly during the day and freely sit out in the open, suggests that they are toxic to predators such as birds. In addition, they secrete a foamy white liquid when really annoyed, which I assume is poisonous or at least very bad tasting.
During the flight that day, I estimated that I saw around 150 males in flight. I only saw two females which is not entirely surprising as they are larger and much heavier than the males, and seem to not fly much until they have laid their first batch of eggs. The flight season of this species lasts only a few weeks and the moths do not feed. They reproduce, then die, like their relatives the giant silk moths.
These fascinating moths have an unusual life history and the taxonomy of the group is the subject of considerable debate. I have a summary of these issues, plus an extended photo series and short video on my buck moth flickr page.
I am surprised that buck moths haven’t been recorded in Iowa before now. State records are always cool, but when they are something this charismatic…
I can relate. The first time I saw buck moths was in the Nebraska Sand Hills – I kept seeing these moths blowing by me so fast I couldn’t figure out what they were. Finally I nabbed one in the net and realized what it was. Way cool!
I was surprised as well, especially after I looked at some range maps. H. maia, the southern/eastern oak feeder, still hasn’t been found in Iowa despite much of the southern part of the state being dominated by oak forest. The other thing that is strange about this occurrence is that Tim Orwig spent a lot of time back in the 80s looking for Leonard’s Skipper all over the Loess Hills when the moth would be flying, and didn’t see a single Buck Moth. And, as you know, they are hard to miss when they are flying. Speaking of the ones in the Sand Hills–take a look at some photos of the larva from out there (there are some on BugGuide I think)–they are way different than mine.
[...] feeds on Redroot (Ceanothus americanus), which is also the foodplant for the Iowa population of Nevada Buckmoth and the rare Mottled Duskywing, and I had found it at the buckmoth site in the Loess Hills last [...]