September 20, 2011 9 Comments
…prairie dock (Silphium terebinthinaceum) in bloom…
…and prairie tiger beetles (Cicindelidia obsoleta vulturina) on the prowl…
On the last weekend of August I made another trip to the White River Hills of north-central Arkansas in a last gasp effort to confirm the occurrence in the area of the swift tiger beetle (Cylindera celeripes). Records of this species include a single individual collected in 1996 at a site near Calico Rock, but two trips to the area this past June had already failed to reveal its presence. I didn’t really expect that I would find it this time either, and such was the case. However, what I was expecting/hoping to see was the beginning of the fall emergence of the prairie tiger beetle. The Missouri/Arkansas disjunct population of this handsome species is perhaps my favorite tiger beetle of all, not only because of its good looks but because of the many spectacular fall collecting trips I’ve taken through the White River Hills to look for it. In this regard I had success, although only two individuals were seen all day long. The area around Calico Rock seemed dry, apparently having been missed by the thunderstorms that rolled through the area a week earlier and that would have surely triggered full bore adult emergence.
The following day I returned to Caney Mountain Conservation Area on the Missouri side, where last fall I had finally found prairie tiger beetles after years of searching what must be the extreme northeasternmost limit of its distribution. Fresh evidence of recent rains was seen, and accordingly the beetles were out in fairly decent numbers in the same area where I found them last fall. I took the opportunity to photograph a few individuals (which I had not done last year) and then turned my attention to looking for other insects. I had my eye out for the spectacularly beautiful bumelia borer (Plinthocoelium suaveolens) and eventually found one. I hoped also to see the marvelously monstrous Microstylum morosum (North America’s largest robber fly), which I found at this site in 2009 as a new state record and was rewarded with two individuals (these will serve as vouchers for the state record, since I didn’t collect it in 2009). Temperatures were rather warm and both of these latter species are traditional “summer” species; however, the presence of prairie tiger beetles, the tawny tinge to the prairie grasses, and the noticeably longer shadows under a deep blue sky told me that fall was, indeed, on the way.
While prairie tiger beetles are (at least for me) the most iconic harbinger of fall in the White River Hills, another classic fall sight was the thick stands of prairie dock plants with their tall, bolting flower spikes. In Missouri this plant serves as a larval host for the longhorned beetle Ataxia hubbardi. In my early years of collecting in Missouri’s glades, I delighted in finding adults of these beetles clinging to the flower stalks during fall—presumably laying eggs from which larvae would hatch and bore down into the tap-root. Although commonly regarded as a pest in sunflower in the southern Great Plains, individuals associated with prairie dock in Missouri’s glades seem different—smaller, narrower, and darker—than those found on sunflower and other more common hosts. Additional material will be needed to make a final assessment on whether these individuals represent a distinct taxon; however, I have not been able to find this species on prairie dock in Missouri since I moved back to the state nearly 16 years ago. The reason for this sudden disappearance remains a mystery, and perhaps it is purely coincidental that the Missouri Department of Conservation began managing all of their glades with prescribed burns during my previous 5-year absence from the state. In the meantime, I will continue to examine prairie dock stems every fall in the hopes that once again I will find the beetles and be able to come to a decision about their taxonomic status. Perhaps I should re-focus my efforts in “low quality” (i.e., never-burned) gladey roadsides rather than our state’s “high quality” (i.e., high floral diversity) natural areas.
Copyright © Ted C. MacRae 2011