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Howdy, BugFans,
The original Buck moth episode was written in 2010, so the BugLady decided to check on the present status of the moths. New words, new pictures.
One of the BugLady’s favorite moths is the Buck moth, whose story here in Wisconsin is a complex one. Buck moths are members of the usually-summertime, usually-nocturnal silk moth family Saturniidae, home of the Cecropia and Luna moths, but Buck moths are active on warm afternoons in mid-fall. They are handsome moths with a 2” to 2 ½” wingspan (females are a bit larger than males; males have feathery antennae and red/orange segments at the rear). There are 23 species in the genus, and some are spectacular, indeed Hemileuca neumoegeni – Hemileuca burnsi – BugGuide.Net, Hemileuca – Hemileuca hera – BugGuide.Net, moth – Hemileuca neumoegeni – BugGuide.Net.
One explanation of their name is that they are out during the hunting season when whitetail bucks are in rut. The Wild Silk Moths of North America passes on another explanation, which has been repeated in folklore since the early 1700’s. Dead bucks were found with a glut of maggots or “bots” in their throats. These eventually [allegedly] turned into “the finest butterfly imaginable, being very large with black, white and yellow stripes.” The theory further explains that “bucks breed their [the buck moths] caterpillars in their heads and blow them out their nostrils.”
The BugLady finds Buck moths in the bog in October. Like many of their larger silk moth relatives, the adults have no mouthparts, do not feed, and get right at the task of ensuring another generation. Female Buck moths use pheromones to attract males, and the BugLady found tantalizing references to Buck moths being attracted to the webs of orb-weaving spiders because of the orb-weavers’ use of “pheromone mimicry.”
Researchers Andrew Warren and Paul Stevens investigated this phenomenon and found that males of some Hemiluca species (but not Hemiluca maia or H. nevadensis) are indeed attracted to pheromones in the webs of Argiope orb weavers (they worked with Black and Yellow Garden spiders). They considered whether the late-flying life cycle of the moths may have evolved as a way to avoid spiders.
When they are startled, they are as likely to fold their wings and drop into the vegetation below as they are to fly away.
In the bog, the caterpillar host plant is Bogbean or Buckbean. Female Buck moths lay a cuff of eggs in fall, but not on Bogbean, because that dies back in fall, so she may use bog birch or she may just toss the eggs on the ground and let the caterpillars find their own food when they hatch in spring. Until they find some, they’re pretty catholic feeders. During the first half of their caterpillar-hood, the shiny, black larvae are gregarious Hemileuca nevadensis – BugGuide.Net. There is some speculation that a mass of dark caterpillars has both a thermal advantage (dark colors absorb the sun’s rays better and they share their minimal body heat) and an anti-predator advantage (diving into a mass of spiny worms is off-putting). Later, they go their separate ways. There are observations of caterpillars swimming from one food plant to another, a sight the BugLady would love to see, though other sources say that the caterpillars can’t swim. Caterpillars pupate in early summer and the adults emerge in fall – unless they decide to remain in the pupa until the following year.
As for the caterpillars? Look but don’t touch. They start out bristly and get bristlier and spinier and more decorative as they age. Some of the spines are hollow and contain a poison that may cause initial nausea, pain comparable to a bee sting, itching/burning, swelling, and redness that may last more than a week, and the spines get more toxic as the caterpillar ages. First aid includes gently applying the sticky side of duct tape to the site to remove spines (good for cactus encounters, too), washing, ice packs and steroid creams or baking soda. At the risk of stating the obvious, several sources suggest that the best way to avoid receiving stings is to avoid handling caterpillars that have spines.
Into the taxonomic weeds with the Buck moth:
Wisconsin’s Buck moths are a bit of a taxonomic mystery. Most species of Buck moths are western. The Buck moth that occurs in the bog may be Hemileuca maia, the Eastern Buck moth, but it is more likely Hemileuca nevadensis, the Nevada Buck moth, or it may be the elusive Midwestern fen Buck moth Hemileuca sp 3, which may turn out to be nevadensis (if nevadensis is indeed a full species), or possibly a new species or an intergrade between nevadensis and maia. There are no morphological distinctions between the three (or four). The Midwestern fen Buck moth is listed as endangered/threatened in a number of Midwestern states despite the fact that its species has not been pinned down. Cutting edge entomology right here on BOTW, once again.
But you get the picture – it’s a confusing group, and caterpillars are often identified by their food plants. The BugLady is proceeding on the assumption that these are nevadensis, because of the food plant. One theory is that nevadensis, which has an interesting checkerboard range extending north and east from southern California to a few spots in New England (Species Hemileuca nevadensis – Nevada Buck Moth – Hodges#7731 – BugGuide.Net), expanded its range into the Midwest post-glacially, and here it adapted to new habitats (areas with high ground water) and to new food plants (the fen-loving Bogbean, Menyanthes trifoliata, which is common in the bog).
H. maia eats oaks; the western nevadensis eats willow and poplar; the more northern populations of nevadensis add Bog Birch, which is also common in the bog. Caterpillars from the Buckbean-loving group can eat other plants, but those not from the Buckbean group can’t tolerate Buckbean. And then there’s an interesting account of a population of larvae at a site between Milwaukee and Madison eating purple loosestrife.
Since this episode was written in 2010, some work has been done by scientists attempting to unravel the relationships between H. maia and H. nevadensis and to figure out exactly who the buckbean-eating Buck moths are. Part of the impetus has come from New York state, which now recognizes fen-living Buck moths (Bogbean Buck moths) as either the subspecies Hemiluca maia menyanthevora (which is Federally endangered) or as H. iroquois, a full species. Same critter – dueling names. The Wisconsin Bog bean eating populations may be a separate lineage.
The BugLady was once contacted by a guy who wondered if maybe she could find a Buck moth pupa and send it to him. That was a hard No. First, the pupal cases are usually hidden in the leaf litter on whatever high ground is available in a fen; and second, whatever species we have locally is, at least, a Species of Special Concern, and may be designated as Endangered or Threatened, so it would possibly be illegal (and certainly immoral) to provide him with a pupa, especially since she strongly suspected that he was going to kill and pin the moth when it emerged (a little detail that he neglected to mention).
Whoever they are, if they were ever common, they no longer are, with populations sometimes restricted to small, isolated pockets within wetlands. They are threatened by the usual suspects – habitat loss (both wetland loss/degradation, and loss of specific habitat for the sun-loving Buckbean), invasive plants, pollution, and climate change.
As Karen Rachel Sime said in an article in The Revelator (Environmental News and Commentary from the Center for Biological Diversity), “The beauty of the mating flight, with hundreds of black-and-white moths set against the backdrop of fall colors, is a privilege to see, and I hope that it can be preserved.”
Stay tuned.
The BugLady