Month: November 2010

Forgotten Foto Friday: Centruroides vittatus

/ Ted C. MacRae / 12 Comments

I got this idea from Doug Taron over at Gossamer Tapestry, who credits Steve Borichevsky at Shooting my Universe for an occasional feature called Forgotten Photo Friday (hopefully my use of the alternative spelling “Foto” won’t be considered too presumptuous).  Perfect timing, as I recently ran across these photos of Centruroides vittatus (striped bark scorpion) that I took last fall after finding him secreted under a rock in a dolomite glade at White River Balds Natural Area in extreme southwest Missouri.  One other photo from the series did make it onto the blog last year – an extreme closeup of his seemingly “smiling” face (see A face only a mother could love), and while these photos are less extreme, I think they still deserve to be shared nevertheless.



One thing that strikes me about this individual is how marvelously well-matched is his coloration with that of the surrounding rocks – a perfect example of the cryptic coloration that characterizes most members of the family (Buthidae) to which this species belongs.

Photo Details: Canon 50D w/ 100mm macro lens (ISO 100, 1/250 sec, f/13-16), Canon MT-24EX flash (1/4 ratio) w/ Sto-Fen. Typical post-processing (levels, minor cropping, unsharp mask).

Copyright © Ted C. MacRae 2010

Cicindela nebraskana – Prairie Long-lipped Tiger Beetle

/ Ted C. MacRae / 14 Comments

Cicindela nebraskana - the prairie long-lipped tiger beetle

We were only halfway through Day of five days in the field and had already achieved Goal of the trip.  Despite that, it took a few hours before Chris and I were ready to tear ourselves away from our first stop in Fall River Co., South Dakota, where we were treated to the sight of glittering, wine-red adults of Cicindela pulchra bejeweling the charcoal-colored shale slopes.  However, the list of species that we wanted to see over the next several days was long, and eventually our pulchra-fever abated (barely) enough to head south to the Pine Ridge in Sioux Co., Nebraska to look for A-list Species – Cicindela nebraskana.  Sioux Co., Nebraska is the type locality for this species (thus the name), but in reality it is a more western species whose distribution just barely sneaks into the northwestern corner of Nebraska (Pearson et al. 2006, Spomer et al. 2008).  I first saw this species at this very site two years ago, seeing only a handful of individuals and managing one harshly-sunlit, point-and-shoot image of one of them.  To my knowledge, this remains the only known field photograph of this species.

Shortgrass prairie atop the Pine Ridge, Sioux Co., Nebraska (photo taken September 2008).

This time, with a Canon 50D camera and 100mm macro lens in my backpack, I was much better equipped for vastly improved field photographs, but in contrast to the numerous individuals of C. pulchra that we saw earlier in the day, only a single C. nebraskana would turn up after intensive searching by Chris, Matt Brust, and myself in the vast shortgrass prairie sitting at the type locality atop the Pine Ridge.  I didn’t find it – Matt did – and the general rule with rare tigers is to capture the first individual rather than try to photograph it.  If no others are seen, photographing it later in a terrarium of native soil is better than trying to photograph it in the field and risk letting it escape.  Matt gave it to Chris, and at the end of the day when we realized we were not going to see another one, we prepared a terrarium of native soil, taking care to keep the surface as intact as possible so that an accurate replication of the field situation could be created when we photographed it later.

Tiger beetles "hunker down" when fatigued.

Although I prefer actual field photographs, the nice thing about photographing tiger beetles in confinement is… well, they don’t run away!  That’s not to say it is easy.  While they do settle down if left undisturbed for a while, once you start messing with them they quickly become agitated and start running in circles around the terrarium perimeter.  Much finger prodding is necessary to get them away from the edge and into a good spot for photographs, and rarely do they stay put for long.  When they finally do settle down, they tend to “hunker down” in a most unflattering pose (as above) – lacking the appearance of alertness that gives the true field photos their life.

A ferocious pose is struck after judicious prodding of the face and touching of the antennae.

I’m a persistent (syn. stubborn) sort, however, and I’ve learned that I can wear them down and poke and prod them out of their hunker.  Just a light poke at the face will often make them back up and lift their front slightly – poke again and they often open their jaws half-cocked – a light touch on the tip of one antennae and they’ll turn slightly.  With practice and patience, hunkered down beetles can be coaxed into some remarkably aggressive-looking poses.  I like the last of these photos in particular because the oblique, jaws half-cocked pose shows off two nice features of this species – the quite long labrum (upper lip) compared to most other tiger beetle species, and the bright white labrum and mandibles of the males of this species (in females they are partially or completely dark).  The long labrum and jaws give this species a very long-faced appearance that distinguishes it immediately from the black morphs of Cicindela purpurea audubonii that occur with much greater frequency in the same habitats as C. nebraskana.

Photo Details:
1: Canon 50D w/ MP-E 65mm 1-5X macro lens (ISO 100, 1/250 sec, f/13), Canon MT-24EX flash w/ Sto-Fen + GFPuffer diffusers.
2: Panasonic DMC-FX3 (ISO 100, 1/400 sec, f/5.6), natural light.
3-4: Canon 50D w/ 100mm macro lens (ISO 100, 1/250 sec, f/16), Canon MT-24EX flash w/ Sto-Fen + GFPuffer diffusers.
All photos: Typical post-processing (levels, minor cropping, unsharp mask).

REFERENCES:

Pearson, D. L., C. B. Knisley and C. J. Kazilek. 2006. A Field Guide to the Tiger Beetles of the United States and Canada. Oxford University Press, New York, 227 pp.

Spomer, S. M., M. L. Brust, D. C. Backlund and S. Weins.  2008. Tiger Beetles of South Dakota & Nebraska.University of Nebraska, Department of Entomology, Lincoln, 60 pp.

Copyright © Ted C. MacRae 2010

Halloween ID challenge answer – Argiope trifasciata

/ Ted C. MacRae / 11 Comments

Here is another photo of the spider in the previous post with a closer view of its spiny pedipalps (mouth feeler thingys).  Troy Bartlett and BitB’s own James Trager got it right – the spider is, indeed, Argiope trifasciata, the banded garden spider (a.k.a. banded garden orbweaver, banded argiope, whitebacked garden spider, etc.).   I figured the genus would be easy, but the species might be a little tricky – at least for those in North America who might be tempted to conclude it was the larger A. aurantia (black and yellow garden spider, etc.).  The broken banding on the femora and generally lighter ventral coloration are usually enough to distinguish A. trifasciata from its more conspicuous congener.  Argiope trifasciata is also distinguished as one of the few truly cosmopolitan arthropod species, occurring naturally on all continents except Antarctica.

Both Troy and Dave Walter mentioned the conspicuous stabilimentum (heavy zig-zagging pattern) that Argiope spiders are perhaps best known for and that they often add to the center of their otherwise cryptic webs. Originally thought to possess a web-stabilizing function (hence the name), a variety of alternative explanations have since been proposed.  These include camouflage (to break up the body outline of the spider and make it less visible to predators), web protection (to make the web more visible to birds and prevent them from flying into and damaging it), prey luring (since it reflects ultraviolet light efficiently), thermal protection (by providing a shield against the sun), and a repository for excess silk.   An alternative hypothesis that I had not heard of but mentioned by Dave is that they serve as sponges for accumulating water for the spider to drink.  Webs with stabilimenta are more common and larger in exposed versus sheltered locations, and a recent study by Blackledge and Wenzel (1999) using A. aurantia found that webs with a stabilimentum suffered significantly less damage from birds (45% on average) than those without, but that they also caught fewer insects (34% on average).  The presence or absence of a stabilimentum, however, was not a significant factor in predation of the spiders by birds.  This implies not only a web protective function for the stabilimentum, but that there is an evolutionary trade-off between web protection and foraging success.  These authors concluded that variation in stabilimenta might be accounted for by a cost—benefit trade-off and that the decision by the spider to include a stabilimentum when building a web may be influenced by external factors such as prey density and web exposure.

Specific to A. trifasciata, a less well known but equally interesting aspect of its behavior is the use of web orientation for thermoregulation.   Tolbert (1979), in a study conducted in the southeastern US, found that web orientation was non-random during the hottest part of the summer, when spiders largely occupied east-west oriented webs with their silver/white dorsal surfaces facing south and their dark ventral surfaces facing north, and during October when the situation was reversed.  Orientation of the white/silver dorsal surface towards the sun presumably is done to help lower body temperatures, while orienting the ventral surface of the spider, which changes from silver to black as the spider reaches maturity, would maximize solar radiation for heat gain.  In contrast, Ramirez et al. (2003) found the species in coastal southern California never oriented their webs in a non-random fashion – rather, they always oriented them along an east-to-west axis with the mostly dark ventral surface of their abdomens facing south.  They suggested that dealing with a high heat load is not a significant problem in the predominantly cool environment of coastal southern California and that staying warm is the greater challenge for this mostly fall active species.

I’ll give 6 points to Troy for agreeing with me on everything, 4 to Dave for playing Devil’s advocate with the species and his unique alternative stabilimentum hypothesis, and 2 points to James for agreeing with Troy’s species ID. 🙂

Photo Details: Canon 50D w/ MP-E 65mm 1-5X macro lens (ISO 100, 1/250 sec, f/14), Canon MT-24EX flash w/ Sto-Fen + GFPuffer diffusers. Typical post-processing (levels, minor cropping, unsharp mask).

REFERENCES:

Blackledge, T. A. and J. W. Wenzel. 1999. Do stabilimenta in orb webs attract prey or defend spiders? Behavioral Ecology 10(4):372–376.

Ramirez, M. G., E. A. Wall and M. Medina. 2003. Web orientation of the banded garden spider Argiope trifasciata (Araneae, Araneidae) in a California coastal population. The Journal of Arachnology 31:405–411.

Tolbert, W. W.  1979. Thermal stress of the orb-weaving spider Argiope trifasciata (Araneae).  Oikos 32(3):386–392.

Copyright © Ted C. MacRae 2010