sand scrub

T.G.I.Flyday—Black horse fly (Tabanus atratus)

/ Ted C. MacRae / 9 Comments

In my previous post, I talked about a day trip to a sand scrub remnant in the Lake Wales Ridge of central Florida to find and photograph the endemic Highlands tiger beetle (Cicindelidia highlandensis). Ironically, the dry sand scrub/pine woodland habitats along this ridge are dotted with small lakes and ponds, allowing a rich aquatic flora and fauna to co-exist alongside the xeric specialists. Field mate Chris Brown and I had found and just finished photographing the tiger beetles when we encountered this rather largish lake—bright, white sand surrounding crisp, clear water reflecting white, puffy clouds in a deep, blue sky. ‘Twas a spectacular sight, indeed!

Sand scrub lake

Sand scrub remnant, Lake Wales Ridge, central Florida

As we stood looking at the scenery, I noticed something black on the stem of one of the sedges growing along the water’s edge. Something big and black! As I moved closer I could tell quickly that it was a large horse fly, but it was not simply perched and resting on the sedge—there was something else going on. Moving closer, ever so cautiously so as not to disturb the fly, I eventually realized that it was a female in the act of oviposition. How cool—I’d never witnessed this before with any species of horse fly, so to see it with such a large species was a real treat. I recognized it instantly as Tabanus atratus—commonly called the black horse fly and recognizable as such by its large size, all-black coloration, and distinctively hooked antennae (see 3rd photo below).

Tabanus atratus ovipositing

A Tabanus atratus female oviposits on a stem overhanging the water.

Before we get to the eggs, let’s dispel some misinformation that seems to persist regarding the size of this species (as it does with almost any large insect). Black horse flies are undeniably large, and in fact they are one of the largest horse flies in North America. The more credible sources (e.g., Pechuman et al. 1983, Long 2001) cite body length as ranging from 20–25 mm (up to a full inch in length). Incredibly, the species does not take the honors as North America’s largest horse fly, which goes instead to Tabanus americanus and it’s upper limit of 30 mm (in fact, T. americanus may be the world’s largest horse fly)! There are, however, on-line sources and a few popular field guides (as cited in BugGuide) that state a maximum length of 28 mm for T. atratus. How credible this figure is I cannot say, but I guarantee that the size indications of 30, 40, and even a whopping 50 mm in length found routinely among photos of this species on BugGuide were not derived from careful measurement and almost certainly instead reflect the astonished reactions that such an abnormally large insect can generate! In fact, there are precious few insects in North America that reach lengths as grand as 50 mm (i.e., two full inches)!

Tabanus atratus ovipositing

Lateral view of oviposition.

We approached carefully, again so as not to disturb the female in the middle of her act, and we watched and photographed as she laid the individual eggs one by one, using the tip of her abdomen to carefully arrange them neatly against each other in stacked layers. From a photographic perspective, balancing flash exposure of the all-black adult with the bright-white egg mass presented a real challenge. Added to that was an additional exposure challenge (my desire for a blue-sky background), making it a truly difficult-to-photograph subject. Long (2001) states that T. atratus egg masses can contain anywhere from one hundred to a thousand eggs each, always near water’s edge or somewhere quite close to water. Females are capable of laying three or four of these egg masses, which apparently gradually turn dark as the eggs develop and approach hatch.

Tabanus atratus egg mass

Freshly laid Tabanus atratus egg mass.

Despite this being the first time I’ve ever witnessed oviposition by this species, it seems to be encountered regularly. There are several photos of ovipositing females among the many photos of this species that have been posted to BugGuide. Moreover, descriptions of the egg mass of T. atatus appeared very early in the literature, first by Hart (1895) and then in photographs by Schwardt (1936). The latter author also states “T. atatus deposits its eggs in masses which are so constant in structural plan as to make specific determination of the egg mass readily possible” (as quoted in Bailey 1948). Thus, even if this female had already finished and left her egg mass, it still could have been identified to species.

REFERENCES:

Bailey, N. S. 1948. Notes on Tabanus atratus subsp. nantuckensis Hine (Diptera). Psyche 55(3):131–138 [pdf].

Hart, C. A. 1895. On the entomology of the Illinois River and adjacent water. Illinois State Laboratory of Natural History Bulletin 4:149–273 [eBook].

Jones, C. M. & D. W. Anthony. 1964. The Tabanidae (Diptera) of Florida. U.S. Department of Agriculture, Agricultural Research Service, Technical Bulletin No. 1295, 85 pp. [pdf].

Long, W. 2001. Tabanus atratus (on-line), Animal Diversity Web. Accessed 20 March 2019 at https://animaldiversity.org/accounts/Tabanus_atratus/

Pechuman, L. L., D. W. Webb & H. J. Teskey. 1983. The Diptera, or true flies, of Illinois 1. Tabanidae. Illinois Natural History Survey Bulletin 33(1):1–121 [pdf].

Schwardt, H. I. 1936. Horseflies of Arkansas. Arkansas Agricultural Experiment Station Bulletin 332:14–15, 27–32.

© Ted C. MacRae 2019

 

Revisiting the Highlands tiger beetle (Cicindelidia highlandensis)

/ Ted C. MacRae / 12 Comments

In September 2016, I had the opportunity to attend the Annual Meeting of the Entomological Society of America in Orlando, Florida, which was being held in conjunction with the International Congress of Entomology. My first thought when I made plans to attend these meetings was that this would be a chance for me to get another look at the Highlands tiger beetle (Cicindelidia highlandensis). One of Florida’s rarest endemic tiger beetles, this species is restricted entirely to remnant sand scrub and pine woodland habitats along the Lake Wales Ridge of Polk and Highlands Counties in central Florida (Choate 2003). I was thrilled to have found adults (in good numbers) on my first attempt back in 2009, and I was also thrilled to have successfully managed to photograph the beetle at that time. However, in the years since, I have become increasingly dissatisfied with those photographs—taken during what was my very first year of insect macrophotography. I’ve learned a lot since then about lighting, diffusion, and composition, but perhaps the biggest annoyance of those photographs is the fact that in every one the antennae and/or legs are “clipped”—a result of my being so enamored with my newfound macrophotographic capabilities that I nearly completely ignored other aspects of photographic composition.

Chris Brown photographing Cicindelidia highlandensis

Chris Brown photographs a Highlands tiger beetle.

Chris Brown—long-time field accomplice and himself a tiger beetle aficionado and insect macrophotographer—was also at the meetings, and since he had never seen the Highlands tiger beetle before we made plans to slip away one day and visit the spot where I had seen them back in 2009. I knew our chances of finding them were slim—it was very late in the season (late September), and the species is a so-called “summer species” with peak of adult activity in July and August. We figured, however, that even if we didn’t find adults we would still enjoy the day in the field, and for some time after arriving at the site that’s all it was. Finally, in an open sandy area near a small lake we saw the first adult. I let Chris take his shots, as this was his first opportunity (see photo above), while I continued to search for additional adults. Eventually I found one and began the long process of “whispering” to it to coax it into allowing me the photographs I desired.

Cicindelidia highlandensis

Highlands tiger beetle (Cicindelidia highlandensis).

As you can see in the photograph above, my compositional preferences have changed since I took those first photographs back in 2009. In contrast to the “as close as possible” style that I initially adopted, I now prefer to back off from the beetle enough to include elements of the habitat in which it occurs. While this compositional style may show less detail on the beetle itself, I believe it adds perspective and results in a more interesting and aesthetically pleasing photograph. I also now like to get down as low as I can, often placing the camera directly on the ground rather than always shooting from “elbow-height”, for a more unique perspective of the beetle, and my use of better flash diffusion results in more even lighting and minimizes the distracting specular highlights that are often the hallmark of flash macrophotography.

Cicindelidia highlandensis

This individual demonstrates the thermoregulatory “stilting” behavior of the adults.

Sadly, my flash unit failed soon after I began photographing the beetle, which is a real shame because the beetle began demonstrating the characteristic “stilting” behavior that the adults use for thermoregulation in their hot environment. The photograph above is the only one that I could “rescue” through some rather heavy-handed post-processing to make up for the failure of the flash unit to fire (it is fortunate that I have shifted to routinely using a combination of ambient light and fill-flash rather than flash only, or I would have had not even this photograph to rescue!). I suppose this means I’ll just have to revisit this species once again (now that I have not one but two new flash units!), which isn’t all bad because I would also love to see and photograph once again the moustached tiger beetle (Ellipsoptera hirtilabris), another Florida endemic (or near so) that I saw here also during my first visit but not during this one.

The Highlands tiger beetle belongs to a group of species called the abdominalis species-group, with all four of the included species (C. abdominalis, C. floridana, C. highlandensis, C. scabrosa) occurring in Florida (three of which are endemic or near-endemic to Florida). For those interested, I have seen and photographed all four of the species and presented a “mini-review” with photographs and links to posts with more detailed information about each species, along with a key to the species to allow for their identification.

REFERENCES:

Choate, P. M., Jr. 2003. A Field Guide and Identification Manual for Florida and Eastern U.S. Tiger Beetles.  University Press of Florida, Gainesville, 224 pp.

© Ted C. MacRae 2019