thermoregulation

Photographing the Limestone Tiger Beetle

/ Ted C. MacRae / 9 Comments

Seeing and photographing the beautifully black Prairie Tiger Beetles (Cicindelidia obsoleta vulturina) in southwestern Oklahoma was a lot of fun, but by Day 5 I was ready to look for one of my top goals for the trip—Cicindelidia politula (Limestone Tiger Beetle). Occurring primarily in Texas (but also sneaking up into Oklahoma), this would be my first attempt to search for the species. I had gotten a few localities in northern Texas from trusty colleagues, and I knew the beetles occurred on limestone outcroppings in dry to xeric upland habitats (Pearson et al. 2006)—usually starting in late September.  Nevertheless, I always get a little apprehensive when I drive long distances to look for tiger beetles I’ve never seen before. Will I recognize it? What if I find another, similar looking but more common species and assume I’ve found it? Will the season be right? Many species, especially those associated with xeric habitats, depend on timely rains to make their appearance. Will I find the proper microhabitat? There are sometimes seemingly minor details that can make a habitat suitable or not for a particular species.

Cicindelidia politula politula | Montague Co., Texas

As can be seen by the above photo, I did succeed in finding the species. However, it wasn’t easy, and for the better part of Day 5 I wondered if I would even be able to capture a specimen, much less succeed in photographing the species in its native habitat. I actually saw the first individual of this species in Oklahoma—sitting on the very first exposed limestone rock at the very first locality I went to. My rule for photographing tiger beetles that I’ve never seen before is to collect the first individual and keep it alive in a vial. In the event I never see another individual or fail in my attempts to photograph them in the field, the first individual becomes my voucher specimen and studio backup. Fortunately, I rarely have to resort to studio shots, but in this case I muffed my attempt to capture the specimen! I searched the locality for a good hour and never saw another one until I circled back to where I started, and there it was again (it just had to be the same one). Believe it or not, I muffed the capture attempt once again! That was my last chance at the Oklahoma site, so it was a rather dejected 2-hour drive south to Montague Co. in northern Texas—knowing that I’d seen it and had my shot at it (two shots, actually) but still found myself empty-handed.

A serviceable photo, but like most of confined individuals it suffers from lack of ”pizzazz.”

My luck improved in Montague Co., although not right away or that much when it did. I had just about given up at this second locality when I saw one. This time I used the stalk-and-slap technique followed by a quick pounce to seal down the net around its perimeter and prevent escape by the beetle (they are real good at quickly finding the tiniest gap between the net rim and the ground and then zipping away in a flash). This time I succeeded in capturing the beetle and thus had my voucher, but my pounce was a little too rough on the beetle, resulting in an extruded genital capsule. This made it completely unusable for photographs (imagine a big orange blob sticking out of the butt of the beetle—not good, photographically!). Of course, finding a beetle at the site caused me to spend more time searching, but I never saw another beetle there.

The shiny black to blue-black elytra with white markings absent or limited to the apices are characteristic for the species.

At this point I had a decision to make—if I drove to the next locality on my list (2-hour drive), I probably would not arrive with enough time before sunset to find beetles. I decided not to waste the remaining daylight and instead just bushwhack where I was to look for similar roadside habitats and drive on after sunset. I found another good habitat fairly quickly, and within minutes after starting the search I saw one—and missed it! But then I saw another one—and missed it, too! Now my confidence was shaken, as neither of the two techniques I use most commonly for capturing tiger beetles were working. When I used the “stalk-and-slap” method the beetles always found a gap on the rough, rocky ground and got away, and when I used the “tap-and-sweep” method the beetles would hunker down at first and then fly right after the net passed over them. I would miss a total of eight (eight!) beetles before I finally (finally!) caught one, and then I would miss three more beetles afterwards! That single beetle is shown in the above photographs, which were taken after placing the beetle on a large, flat limestone rock that I laid on the bed in my hotel room that night (carrying that huge limestone rock into the hotel room was an experience!).

I really dislike photographing confined insects. Even if one prepares a wholly natural looking set and manages to cajole the subject into standing still, they rarely look quite right. I do like the first photo in the series, just because it’s a well composed face shot, but I’m not so fond of the more ‘classic’ view of the beetle represented by the second photo. Technically it’s an adequate photo that shows the beetle and all of its salient characters; however, it lacks, well… oomph, because the beetle isn’t really doing anything—the photo tells no natural history story. Still, an adequate photo that lacks oomph is better than no photo at all, so I made the best of my opportunity to take studio shots of the one good beetle I had and hoped for better luck the next day.

Exposed limestone road bank in Johnson Co., Texas—perfect habitat for Cicindelidia politula

The next day brought the luck that I was looking for. I was close to the next locality on my list when I saw a road bank with exposed limestone that just seemed to call out, “Search me!” I stopped and began searching, and within a few minutes I saw the first beetle—and missed it! Arghhh, not again! I would actually miss a few more before I finally caught one, so by now my confidence was destroyed. It’s been a long since I’ve had this much trouble catching tiger beetles, and if I was having this much trouble catching them, how on earth could I even contemplate trying to photograph them. However, the nice thing about finding a spot where beetles are out in numbers is the opportunity to try again—practice makes perfect. I decided my previous attempts had all been a little too lackadaisical and started buckling down and really concentrating on my technique. Not surprisingly, I started having success in capturing the elusive beetles (tap-and-sweep worked best), and after a time I felt like I had a good enough feel for the beetle’s behavior to begin trying for field photographs.

Cicindelidia politula politula | Johnson Co., Texas

Not surprisingly, given how difficult they were to catch, this also proved to be one of the most difficult species of tiger beetle that I’ve ever tried to photograph. Like many other tiger beetles that live in hot, xeric, open habitats they were extremely wary and difficult to approach, a behavior that was exacerbated by the now midday sun. Their escape flights were not very far, but far enough that if I’d already gotten into a prone position I had to get up and start all over again. The task was made even more difficult by the hard, jagged, rough-edge rocks on which I had to lay and crawl—ouch! Several individuals are represented in the field photographs shown here, each of which I had to “work” for some amount of time before I was able to finally get close enough to start taking photos (and representing only a few of the many individuals that I actually spent time “working”). Usually, the first photos of an individual are never very good but start the process of getting the beetle accustomed to my presence and the periodic flash of light. Eventually, if I’m lucky, it settles down and resumes normal searching and thermoregulatory behaviors, and I can then get as close as I want and really work the angles for a variety of compositions. I no longer try to approach beetles from the ‘proper’ angle; they turn so much while moving about that it’s easier to just wait for them to assume desired angles as they move about and be ready to shoot when it happens. Field photography of unconfined tiger beetles in their native habitat is hard and time consuming, but the results are well worth the effort. Compare the staged photos of the Montague Co. individual with the field photos from Johnson Co. What marvelous displays of active beetles engaged in natural behaviors in their native habitat the latter represent!

By midday the adults start ”sun-facing” to minimize thermal exposure in their hot, xeric habitats.

After getting several good photos of the beetle in its habitat, I decided it was time to try for some really close photos and added a full set of extension tubes to the camera. A set of tubes with a 100mm macro lens provides close to 2X magnification, but it also reduces the available working distance—a real challenge with wary tiger beetles under a midday sun! I spent quite a bit of time trying to get close enough to take advantage of the additional magnification, but I wasn’t successful until I encountered the individual in the photos below shade-seeking at the base of a yucca plant. Shade-seeking beetles tend to stay put and not move as much (although they still rarely just sit there).

Shade-seeking is another strategy to avoid the midday heat.

I worked this beetle for several minutes and managed to get a number of shots, each closer than the previous and culminating in the nice portrait below.

The ”pièce de résistance”—Cicindelidia politula politula at 2X life size!

My photographic appetite now completely satiated, I spent the rest of the day searching for (and finding) additional localities for the species in the area. I found them more often associated with older, level exposures that had at least a small amount of vegetation. In contrast, newer or steeply sloped exposures or those completely devoid of vegetation rarely had beetles associated with them. I had now spent two days working on C. politula, but the results—both as a collector and as a photographer—made it time well spent. I felt like I “understood” the beetle. However, with only two days left in the trip, it was time to start working my way back towards Missouri and focusing on the few additional goals I still had for the trip.

REFERENCE:

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.

Copyright © Ted C. MacRae 2012

Colorado’s Great Sand Dunes Tiger Beetle

/ Ted C. MacRae / 19 Comments

Great Sand Dunes National Park | Saguache and Alamosa Counties, Colorado (click for 1680 x 887 version)

Last year’s Annual Fall Tiger Beetle Trip entered its last day as an unqualified success. Travel partner Jeff Huether and I were doing the “Great Western Sand Dune Tour” on a quest to find and photograph some of North America’s most geographically restricted tiger beetles. The first four days featured successful visits to northwestern Colorado’s Maybell Sand Dunes for Cicindela scutellaris yampae and Cicindela formosa gibsoni, southeastern Idaho’s St. Anthony Sand Dunes for Cicindela arenicola, and southwestern Utah’s Coral Pink Sand Dunes for the prize of the trip—Cicindela albissima. The only endemic that we had failed to find was Cicindela waynei at southwestern Idaho’s Bruneau Sand Dunes (hopefully this was a result of poor fall emergence conditions rather than an indication of further decline of this perilously endangered species).

Small sand dune west of GSDNP in the Nature Conservancy's Medano-Zapata Ranch.

Day 5 featured a visit to southwestern Colorado’s Great Sand Dunes to look for the endemic Cicindela theatina. As on every day previous of the trip, the morning drive saw cool but rising temperatures under bright, sunny skies, so we were optimistic about our chances. Between Great Sand Dunes National Park (type locality of the beetle) and The Nature Conservancy’s Medano-Zapata Ranch west of the park, the entire 290 km² range of C. theatina is on protected land. Not knowing whether the beetle would be out and, if so, how extensively it would occur, our plan was to approach the Park from the west through Zapata Ranch and stop at any sand dunes we sighted along the way until we found the beetle.  It didn’t take long—as soon as we entered the Ranch we began to see small sand dunes in the distance, and within minutes after making the 1-km hike towards one particularly promising looking dune we saw the beetles. Even though this was the fifth western sand dune endemic I had seen in as many days, the first moment I laid eyes upon it was no less exciting—flashing red and green on coppery, white marked elytra, it seemed all hair and teeth!

Great Sand Dunes tiger beetle (Cicindela theatina) | Medano-Zapata Ranch

Despite this being my first sighting of the species, there was no doubt about it’s identity. The only other tiger beetle that occurs with and could possibly be mistaken for C. theatina is the blowout tiger beetle, C. lengi; however, the broad marginal band that runs completely around the elytra and the green/brown dorsal coloration of C. theatina are enough to distinguish it from that species. Temperatures were still a bit on the cool side, but the beetles were already remarkably active and skittish. Like the other sand dune species we had already seen, they were enormously difficult to approach—numerous failed attempts were necessary before I encountered the slightly more cooperative female shown in these photos (although she still required several minutes of stalking to get her sufficiently accustomed to my presence to allow these shots).

Like most sand dune tiger beetles, adults are densely hairy on the lateral and ventral surfaces.

Adults ''hug'' the sand for warmth during the cooler morning hours.

The dense covering of white hairs on the lateral and ventral surfaces of the adults belies their adaptation to the abrading sands of their wind-swept habitat. Scouring sands, however, are not the only hardships that the adults must contend with. Temperatures on the dunes can range from as low as 40° F on a chilly morning to nearly 140° F during the heat of the day. Accordingly, much of the adult beetle’s activities revolve around thermoregulation to maintain optimal body temperatures for activity (Pineda and Kondratieff 2003). These include not only stilting, shade-seeking, and mid-day burrowing to avoid excessive warming (see my post  for examples of these behaviors), but basking to gain warmth when temperatures are still a bit too cool for effective foraging (photo above).

Fabulous metallic red and green highlights on the head and pronotum contrast with the reddish brown elytra and their white lateral markings.

Despite the fact that the entire range of this species is encompassed by protected land, WildEarth Guardians filed a petition for federal listing as an endangered species in 2007 (Tweit 2010). Whether protection will be granted remains to be seen—Coral Pink’s C. albissima has a global range only 1.3% the size of C. theatina‘s range (only slightly more than half of which is on protected land), yet that species has been awaiting listing for nearly three decades now! (Too bad C. theatina doesn’t have real fur, feathers, or those endearing mammalian eyes that would surely allow it to jump to the front of the line.)

For the first time in BitB Challenge history, we have a 4-way tie for the win. Dorian Patkus, Mr. Phidippus, Mike Baker, and David Winter all share the honors for . Mr. Phidippus is the big winner, however, as he strengthens his grip on the overall lead with a lead of 13 or more points over his nearest rivals (Roy, Tim Eisele, Mike Baker, and Dennis Haines). The competition is far from over though—a single misstep is all it would take to see the emergence of a new leader before this session is over.

REFERENCES:

Pineda P. M. and B. C. Kondratieff. 2003. Natural history of the Colorado Great Sand Dunes tiger beetle, Cicindela theatina Rotger. Transactions of the American Entomological Society 129(3/4):333–360.

Tweit, S. J. 2010. Beetle Mania. National Parks 84(4):24–25.

Copyright © Ted C. MacRae 2012

Monroe Canyon epilogue – Audubon’s tiger beetle

/ Ted C. MacRae / 20 Comments

Cicindela purpurea audubonii (Audubon's tiger beetle) - green morph

In my first post about Monroe Canyon in the Pine Ridge of northwestern Nebraska, I featured the sumptuous Cicindela lengi (blowout tiger beetle) – a target species for the trip and one of six tiger beetle species that Chris Brown and I would find at this quarter-mile long sandy roadside embankment.  Another species we found there was C. denverensis (green claybank tiger beetle), unexpected given its preference for clay soils, but like C. lengi also a target species and thus a welcome find.  We also saw some more common species – the nominotypical forms of C. formosa (big sand tiger beetle) and C. scutellaris (festive tiger beetle), both reliable residents of sand habitats throughout the Great Plains, as well as a few individuals of the often ubiquitous C. punctulata (punctured tiger beetle).  The most numerous of all, however, was C. purpurea audubonii (Audubon’s tiger beetle).  Despite being uncommon in other parts of its range (in fact, nominotypical populations are feared extirpated in some parts of the eastern U.S.), C. purpurea audubonii is one of the most commonly encountered tiger beetles in grassland habitats throughout the central Great Plains and Rocky Mountains.  This species belongs to a complex of several that are generally green in color and fond of clay soil habitats, such as C. denverensis, C. decemnotata (badlands tiger beetle), C. limbalis (common claybank tiger beetle), and C. splendida (splendid tiger beetle).  All of these species can co-occur with C. purpurea audubonii in the Great Plains, but the latter is distinguished by its faint purple tinge and distinct metallic purple border around the edge of the elytra and its reduced elytral markings consisting of a short, oblique middle line and a white rear tip at the edge of the elytra (Pearson et al. 2006).  All of these characters can be seen easily in classic pose in the above photograph.

Cicindela purpurea audubonii (Audubon's tiger beetle) - black morph

Despite its commonness, however, I actually did look forward to seeing this species – the reason being the occurrence of occasional all-black individuals in the population.  Tiger beetles as a whole are a variable lot – polytopism (geographically based variability) is the rule!  Despite this, for the most part individuals within a given population usually exhibit a fairly uniform appearance.  Occasionally, populations of some species – generally those at intergrade zones where different subspecies meet – will show variation on a continuum between two extremes.  The occurrence of two distinct morphs within a population, however, is rather unusual.  I lacked good field photographs of the all-black morph of C. purpurea audubonii (and also the green morph, for that matter), so I was pleased to encounter several individuals of the black morph while we were at Monroe Canyon.  As can be seen in the above photograph, black morph individuals are truly all-black, perhaps with a purple reflection but without a trace of green anywhere on the body.  They do retain the same pattern of reduced white markings exhibited by the green morphs.  As a result, these individuals can be confused with some other black species that also occur in the Great Plains, such as C. nebraskana (prairie long-lipped tiger beetle) and, at higher elevations, C. longilabris (boreal long-lipped tiger beetle).  These latter species were also targets for our trip, so we had to pay close attention to any black morphs that we saw to confirm their identity (C. purpurea audubonii black morphs are distinguished by their distinctly hairy frons).

Chris Brown waits patiently to photograph a burrowing wolf spider at the entrance of its burrow.

I’ve not been able to find any additional information about these black morph individuals and the possible causes for their occurrence.  Cicindela purpurea is a so-called “spring-fall” species, emerging in the fall as sexually immature adults and then spending the winter in burrows before re-emerging in the spring to mate and lay eggs.  As spring-fall species go, it is one of the earliest to appear in the spring and last to disappear in the fall.¹  This immediately brings to my mind a possible thermoregulatory function.  Low temperatures may be a challenge for the adults during early spring and late fall, and the black coloration could be an adaptation to maximize absorption of solar radiation for heat gain. This idea seems to be supported by the fact that the incidence of black morphs is greater at more northern latitudes and in the higher elevations of the western part of the subspecies’ range (as much as 20-40%), where overall lower temperatures would be expected to occur.

¹ Karl Werner even amusingly stated that this species “rather delights in chilly weather” (Acorn 2001).

REFERENCES:

Acorn, J.  2001. Tiger Beetles of Alberta: Killers on the Clay, Stalkers on the Sand. The University of Alberta Press, Edmonton, xix + 120 pp.

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.

Copyright © Ted C. MacRae 2011

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