Arthropoda

Arthropods – insects, arachnids, crustaceans, myriapods, & relatives

Ghosts in the night

/ Ted C. MacRae / 3 Comments

This summer I’ve spent quite a few nights hanging out along the Mississippi River—lamp on my head, vials in my pocket, and an ultraviolet (UV) light setup on the sandy banks. UV light collecting for insects (also called “blacklighting”) is a popular method among us beetlers, but for a number of reasons it’s been a while since I’ve done a lot of heavy blacklighting myself. That all changed this year when I decided I needed to get a better handle on the Missouri distribution of two species of tiger beetles, Ellipsoptera cuprascens and E. macra, found only in sandy habitats along the shores of the state’s two big rivers—the Missouri and Mississippi—and, fortuitously, attracted to blacklights at night. Blacklighting alongside these big rivers is a relatively new experience for me, as my previous experiences have been mostly in forests—either here in the Midwest or out in the desert southwest. Along the big rivers, as soon as the sun dips below the horizon hordes of hungry mosquitos descend upon me and choking swarms of caddisflies quickly envelop the blacklight. Liberal application of Deet keeps the mosquitoes at bay, but checking the sheet behind the blacklight to see if anything of interest has landed requires a bit of a mad dash and a quick retreat, all the while holding my breath and clamping the shirt cuff around my neck to prevent the swarming bugs from flying into spaces where I don’t want them.

Arctosa littoralis (beach wolf spider) | Lewis Co., Missouri

Wandering away from the blacklight and exploring along the beach in the black of night is also a relatively new experience. While I’ve done a fair bit of night collecting away from the light, again this has tended to be in forests and woodlands with a beating sheet in hand looking for jewel beetles, which still hang out on the same host plants they can be found on during the day but are far less inclined to zip away as soon as they hit the sheet like they do when the sun is high overhead. I haven’t spent much time shining a lamp on the sand of a big river beach, so I wasn’t quite sure what to expect (other than hopefully a tiger beetle!). As I walked along the beach, I occasionally saw blue-green glowing dots on the sand—I recognized these fairly quickly as the eyes of spiders reflecting the light from my headlamp. However, at first when looked closer at the spot where I thought a spider should be sitting I didn’t see anything. It took a few tries before finally I saw ghost-like movement on the sand, and when I moved cautiously and got down close to the sand I finally saw a magnificent, white wolf spider sitting motionless—perfectly colored to blend into the sand on which it was sitting.

The mottled, white coloration is conspicuous on wet sand…

I quickly hurried back to the car and got my camera, set it up with a 100mm macro lens and extension tubes (hoping I could get real close), and went back to the spot where I’d seen the spider to see if I could find it again. I didn’t, but not too much searching was required before I found another one. Unfortunately, I didn’t succeed in photographing that one either. It was apparent to me that I was going to have to use the same ultra-cautious and slow movements that I use with tiger beetles if I was going to succeed in photographing one or more of these spiders. I quickly figured out that they were easier to see if I looked right along the water’s edge, as in that situation the white coloration of the spider actually stood out against the darkened, wet sand. (Of course, photographing them on the wet sand was a tad dirtier for me, but I’m not afraid to get filthy dirty when it comes to photographing arthropods.) I also figured out that I could more easily find the spiders on the wet sand and then follow them up to the drier sand for photos that better showed just how marvelously cryptic their coloration was.

…but provides perfect camouflage on the dry sand further away from the water’s edge.

Those of you familiar with my work know that I love frontal portraits, but I found this to be almost impossible during my first attempts. It was hard enough approaching the spider from the front without it bolting before I could get set behind the camera, but in the few cases where I did actually manage this then it would bolt as soon as I made any microadjustment in the position of the camera to compose the shot. It occurred to me that the spider was sensing vibration from moving the camera on the ground (ground-resting the camera is a technique that I use commonly to get the lowest possible angle on my subjects)—makes sense, as spiders are intensely tuned into vibrations for  prey capture. Once I began keeping my hand flat under the camera as sort of a makeshift “beanbag” I was able to make the final adjustments necessary to get shots like the one shown below and in ID Challenge #20.

Active primarily at night, the spider’s eyes glow blue-green when hit by light.

According to Dondale & Redner (1983) this should be Arctosa littoralis—widespread in littoral habitats across North America but, at least at the time of their revision, not recorded from Missouri [in fact, it seems no species of Arctosa was known from Missouri until A. virgo was recorded from oak-hickory forests in the southern part of the state by Bultman (1992)]. I’ll leave it to the spiderphiles to determine if this actually represents a new state record or (more likely) if I just haven’t dug deep enough into the literature.

Congratulations to 3-time champ Ben Coulter, who swooped in from his hiding place with 30 pts to win ID Challenge #20—the final challenge of BitB Challenge Session #6. It wasn’t enough, however, to disturb the overall standings, and Brady Richards maintained his overall lead with 28 pts to win Session #6. Sam Heads was just one point away from the win in this challenge, but his 29 pts were enough to earn a tie for 2nd place in the overall standings with Mr. Phidippus, who finished a respectable 4th place in this challenge. Nobody else came close to these three gentlemen in the overalls, so they deserve their accolades and loot (please contact me for details on the available choices). In case you haven’t been following along, here is a summary of the BitB Challenge champions to this point, listed by session:

  1. Ben Coulter
  2. Ben Coulter
  3. Max Barclay
  4. Ben Coulter
  5. Mr. Phidippus
  6. Brady Richards

REFERENCES:

Bultman, T. L. 1992. Abundance and association of cursorial spiders from calcareous fens in southern Missouri. Journal of Arachnology 20:165–172.

Dondale, C. D. & J. H. Redner. 1983. Revision of the wolf spiders of the genus Arctosa C . L. Koch in North and Central America (Araneae: Lycosidae). Journal of Arachnology 11:1–30.

Copyright © Ted C. MacRae 2012

Life at 8X—soybean aphid

/ Ted C. MacRae / 12 Comments

Although my first attempt at adding extension tubes to my Canon MP-E 65mm macro lens, effectively converting it from a 1–5X to a 1.7–8.0X lens, was nearly a year ago, it has only been recently that I’ve actually started experimenting with this combination to obtain high-mag photographs of very small insects in the field. The first example that I showed of such a photograph was a tiny seed weevil (Althaeus sp.) on its hibiscus host plant. I’ve since photographed a number of other insect subjects at high-mag using this setup and am getting a better feel for the capabilities—and limitations—inherent in using it. First, here is what the setup actually looks like:

Canon 50D body, MP-E 65mm macro lens on 68mm extension, MT-24EX twin flash w/ DIY diffuser.

Not the normal photo quality for this site (just a quick field setup photographed with my I-Phone), but it shows just how long the lens component becomes when fully extended to achieve 8X magnification. The camera is quite front-heavy, making the camera difficult to use hand-held, and the very shallow DOF (depth of field) due to the extreme level of magnification makes precise focusing difficult and magnifies the effect of any motion between the camera and subject. Obviously, one solution for these problems is to mount the camera on a tripod and place the subject on a stable surface; however, for reasons I’ve mentioned elsewhere, it is unlikely that I will ever take to bringing a tripod into the field, and the whole point of this exercise is to develop the capability for getting usable hand-held field photographs no matter what level of magnification they may require. As an alternative, I use a number of other techniques, discussed in my prior post on the subject, to stabilize the camera without using a tripod.

One of the recent subjects I photographed with this setup is the soybean aphid, Aphis glycines (order Hemiptera, family Aphididae). This distinctive Asian species has recently established in the U.S. as invasive pest of soybeans; adult females measure only 1–2 mm in length (and the nymphs are even smaller) and can quickly develop very high densities on the leaves and upper stems of soybean plants. The following photograph was taken at the camera setup’s minimum magnification of 1.7X and provides a typical view of adult aphids and their progeny:

Aphis glycines (soybean aphid) | Warren Co., Illinois

While the above photograph does a very good job of showing the colonial appearance of infestations by these aphids on soybean foliage, what about the aphids themselves? It would be nice to get a better look at individual aphids. The following photographs were all taken with the lens fully extended to achieve 8X magnification (and completely hand-held):

Adult female aphid—note the eye spots of the unborn nymphs visible within the body.

Another adult female navigates the hairs on the surface of the soybean leaf (I never knew soybean leaves were so hairy!).

A mother surrounded by her progeny. As above, eye spots of unborn nymphs can be seen inside her body.

These photographs are not without their problems—they are a bit soft, probably due to motion blur that results from the camera being hand-held and the extremely thin DOF that makes it difficult to get all of the desired components of the photos equally in focus. Lighting also is a challenge, as the very small subject-to-lens distance forces light from the flash to come from directly above or even behind the subject while minimizing front lighting (especially evident in the last photo with its straight down view). Nevertheless, these are decent, usable photographs that provide an uncommon view of these exceedingly tiny insects—without the encumbrance of carrying a tripod in the field, the time investment of studio photography and/or focus-stacking, or the expense of a microscope-mounted camera system (for those of us without access to such systems).

Copyright © Ted C. MacRae 2012

ID Challenge #20

/ Ted C. MacRae / 47 Comments

Has it really been seven weeks since the last ID Challenge? BitB Challenge session #6 overall leaders Brady Richards (66 pts), Mr. Phidippus (58 pts), and Sam Heads (54 pts) must think I’m trying to duck the final standings so I don’t have to doll out any loot. Let’s finish this session with a straight up ID Challenge—3 pts for order (der!), 4 pts for family, 5 pts for genus, and (to separate the imagos from the neonates) 6 pts for species. Bonus question worth 5 pts—what is the best way to search for this species? That’s a whopping total of 23 pts up for grabs in this one challenge (not including any discretionary bonus pts that might be awarded), so not only are the leaders not safe from each other, but from any number of other participants lurking just below them in the standings.  Please read the full rules if you are not already familiar with them—good luck!

Copyright © Ted C. MacRae 2012

Shooting 8X hand-held in the field

/ Ted C. MacRae / 11 Comments

Just to prove it can be done, here is an uncropped photograph of the seed weevil Althaeus hibisci (or the closely related A. folkertsi) (order Coleoptera, family Chrysomelidae, subfamily Bruchinae). Adults of these species measure only 1.5–2.5 mm in length (Kingsolver 2004), yet this individual almost completely fills the frame:

Althaeus hibisci/folkertsi on Hibiscus moscheutos lasiocarpus | Route 66 State Park, St. Louis Co., Missouri

I achieved 8X magnification by stacking 68 mm of extension tubes under my Canon MP-E 65mm 1–5X macro lens and extending the bellows of the lens out to its maximum. Shooting 8X is not for the timid—the small subject to lens distance complicates lighting (full flash required), and even finding the subject in the viewfinder can be next to impossible. However, doing it hand-held in the field requires more than just courage and patience—good bracing techniques to minimize movement by and between the camera and the subject are essential. Here is how I do it:

  • I sit down, prop my knees up, and rest the camera in the crotch between my knees (the camera quickly becomes very heavy since it’s being held by only one hand—see next bullet) while positioning it near my face. If possible, I lean back against something as well to provide even more stability, although this is often not possible depending on field conditions.
  • I hold the leaf or flower supporting the subject in my left hand. Subjects this small are rarely going anywhere (or if they are skittish then I use the same slow, deliberate techniques that I use with larger skittish insects), so it is possible to hold the leaf or flower and position the subject right in front of the lens. Hand holding the subject’s support also affords the ability to micro-adjust the position and angle of the subject for optimum composition or to adjust for movement by the subject (easier than trying to track it by moving the lens). In this case of the photo featured here, I detached the leaf with the beetle from the plant (use small scissors to snip the leaf petiole, as this avoids the “jolt” that happens if you try to pick the leaf and which usually results in the subject fleeing). In other cases, I leave the leaf attached and carefully “pull” it towards me to hold it steady.
  • I look through the viewfinder and brace my left wrist (yes, the same hand that is holding the subject) on the underside of the lens, then slowly move the subject towards the lens with my fingers until I see movement and can micro-adjust for proper focus. Bracing your wrist against the lens is key—it is nearly impossible to hold the subject steady in front of the lens without bracing your wrist against it. In effect, this “fixes” the subject to the lens. Also, before I begin looking for the subject through the viewfinder I study its position on the leaf and look for “landmarks” that I can recognize when looking through the viewfinder to minimize the time needed to find the subject (the more time you spend looking for the subject, the greater the chance it will move or flee). Again, the subject to lens distance is very small, but with practice you’ll get a feel for precisely how far from the lens you need to place the subject.
  • I hold my breath and micro-adjust the subject position to nail the focus (usually on the eye) and then fire a shot. If it takes too long to get the focus I exhale and try again, as body shake will only get worse once it starts. Important: After taking the first shot, do not move the hand holding the subject as you look at the image preview and/or histogram—the first shot rarely has the settings precisely where you need them, and keeping the subject in place prevents a lot of re-searching after making the needed setting adjustments with the right hand.

Other than lighting, nailing the focus is the most difficult aspect of shooting hand-held at such high magnifications. The more relaxed and stable you can keep the rest of your body, the less hand movement you’ll experience while holding the subject and the greater chance you have of hitting the focus. Again, a fully extended MP-E lens on 68 mm of extension tubes becomes very heavy very quickly when held in one hand (even when resting on your knees), so expect your forearm muscles to give out quickly until you have a chance to strengthen them through practice.

I use these same techniques to some degree at lower magnifications as well—certainly for anything above 2X. I’m interested in doing a lot more 8X photography, however, because there is a whole world of tiny insects that are not being photographed due to their very small size. These insects are no less fascinating and beautiful than their larger, more oft photographed brethren.

Finally, you might be asking why I don’t just carry a tripod or collect subjects and bring them back to the studio for more controlled conditions. There are many photographers who advocate the use of tripods, but I’m not one of them. I am first and foremost an entomologist, and when I’m in the field I’m generally already carrying at least a net and other equipment for collecting insects. There are opportunity costs involved if I also try to lug a heavy tripod with me. What’s that? I could leave it in the car and then go get it when I need it? Honestly, I would pass on a lot of shots if I had to go back to the car to get something for it. The same goes for studio photography—there are many shots I would simply pass on if getting them meant that I needed to collect subjects, keep them in good condition for the duration of the trip (which might be days or more), and then setup in a studio. Moreover, there are many shots—specifically regarding behavior—that would be impossible with collected subjects. But really, it has mostly to do with what I want to be and portray as an insect photographer, and that is somebody who has the ability to photograph unconfined subjects exhibiting natural behaviors in their native habitats. Having the ability to shoot 8X hand-held in the field if I want to gives me more options and makes me a better photographer.

Do you have any special bracing or stabilizing techniques that you use for high-mag hand-held macrophotography? If so I’d love to hear about them.

REFERENCE:

Kingsolver, J. M. 2004. Handbook of the Bruchidae of the United States and Canada. U.S. Department of Agriculture, Technical Bulletin 1912, 2 volumes, 536 pp.
 
Copyright © Ted C. MacRae 2012

Very cozy tigers!

/ Ted C. MacRae / 2 Comments

In my post Very wary tigers!, I spoke of the frustrations of trying to photograph tiger beetles when conditions of temperature and terrain conspire to make them too wary to approach. This is a common feature of tiger beetle photography in general, but the problem seems to reach its zenith with the “wet sand beach” species—most species inhabiting these habitats tend to be “summer species” active during the hottest part of the season, and their habitats tend to be virtually devoid of any vegetative cover that can be used to the photographer’s advantage. A blazing sun on hot, open sand is not conducive to photographing anything! Still I try, and on that particular day I did manage a few relatively distant photographs of two species, Cicindela repanda (Bronzed Tiger Beetle) and C. hirticollis shelfordi (Shelford’s Hairy-necked Tiger Beetle) but none at all of a third species that was present on the beach, Ellipsoptera cuprascens (Coppery Tiger Beetle).

Ellipsoptera cuprascens (Coppery Tiger Beetle) | New Madrid Co., Missouri

Well, there is always more than one way to skin a cat (or a tiger), and as can be seen in these photographs I took a different approach to that latter species that allowed me to obtain several quite decent photographs of both males and females. Not long after that frustrating day at Cape Rock Park, I found myself again in southeastern Missouri with an opportunity to do some night collecting. It may not be widely known, but certain species of tiger beetles are also active at night and can actually be attracted to ultraviolet (UV) lights. This is particularly true of species in the genus Ellipsoptera, which as a group seem to depend almost exclusively on coastal and fluviatile sand habitats. I have used UV lights in the past to attract nocturnally active species of tiger beetles for photography (see Return to Nowhere), and since I had seen E. cuprascens a few years ago at Steward Towhead in New Madrid County I thought this might be a good spot to try again for photographs of that species.

The relatively coarsely and densely punctate elytra distinguish E. cuprascens from E. macra.

“Might be a good spot” turns out to be quite the understatement, as I have never seen E. cuprascens in such numbers as I did that night! Seeing the species common at the sheet guarantees that individuals will also be found milling around on the ground in the immediate vicinity of the sheet, and unlike during the heat of the day when their bodies shift to thermal overdrive, adults at night are much easier to approach due to the cooler temperatures and the distraction of abundant, easily captured prey sitting transfixed in their UV light-induced stupor. Of course, night photography brings its own set of challenges, primarily (for me) the need to use the camera flash head lamps for focusing—I often find myself repeatedly aborting a shot because the lamps turned off automatically before I had a chance to find the subject and compose the shot to my satisfaction. Still, this is a minor inconvenience compared to the exasperation of subjects blasting across the hot sand when your approach comes within 12 feet!

Males mandibles are modified for grasping the female pronotum during mating.

Ellipsoptera cuprascens is very closely related to E. macra (Sandy Stream Tiger Beetle—see The last tiger beetle), which it resembles greatly and whose ranges overlap here in Missouri (although the latter is far less commonly encountered than the former). The photos in this post show the relatively coarser and denser punctures on the elytra that distinguish E. cuprascens from E. macra, as well as their somewhat shinier surface and distinctly more coppery color. The rounded elytral apices of the female (middle photo) also serve to distinguish the species from E. macra, in which species the elytra of the females come to a point at the suture (Pearson et al. 2006). Note also the sexual dimorphism in the labrum and mandibles of the female (first photo) and male (last photo), with the mandibles relatively longer and slightly curved and the labrum shorter in the latter. Presumably this is related to the use of the mandibles by the males in grasping the female pronotum during mating—the longer, curved mandibles are shaped to precisely fit the contour of the female’s pronotum, while the shorter labrum allows the mandibles to gain better purchase farther down on the side of the female’s pronotum (Pearson and Vogler 2001).

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.

Pearson, D. L. and A. P. Vogler.  2001. Tiger Beetles: The Evolution, Ecology, and Diversity of the Cicindelids.  Cornell University Press, Ithaca, New York, 333 pp.

Copyright © Ted C. MacRae 2012

Very wary tigers!

/ Ted C. MacRae / 8 Comments

In late July I found a new tiger beetle site in southeastern Missouri—a small sandbar along the Mississippi River near Cape Rock Park on the north side of Cape Girardeau. I originally went to the park to look for Cylindera cursitans (Antlike Tiger Beetle), two specimens of which my friend and colleague Kent Fothergill had found in the collection of a local lepidopterist (MacRae et al. 2012). I thoroughly searched the areas that looked suitable for that species, but to no avail. I did, however, spot the sandbar down by the river and knew immediately that it had good potential for several species typically found in such habitats. Even before hiking down the rocky embankment I figured I would see Cicindela repanda (Bronze Tiger Beetle)—dreadfully common along almost every waterway in the state. What I was really hoping to see, however, were some of the more specialty species found only in wet sand habitats along the big rivers of the state—the Missouri and mighty Mississippi.

”Stilting” and ”sun-facing” by Cicindela hirticollis shelfordi | Cape Girardeau Co., Missouri

Predictably, C. repanda was present and abundant, but it wasn’t long before I spotted some individuals that looked just a little bit different—stockier and with the white markings a little more distinct. A closer look confirmed that these were C. hirticollis shelfordi (Shelford’s Hairy-necked Tiger Beetle). It had been a while since I’d seen this species, and it occurred to me that the only photos I had of it were taken with my point-and-shoot prior to getting my dSLR setup. I then realized also that I didn’t even have good photographs of C. repanda—I’ve been so focused on photographing rare and unusual species over the past few years that I’ve completely neglected photographing our state’s most common resident.

Sand bar habitat along the Mississippi River | Cape Girardeau Co., Missouri.

Over the years, I’ve learned a number of tricks that have allowed me to be fairly successful at approaching tiger beetles closely for photography—working a population to find that one slightly more cooperative individual, and then working that one individual until it becomes accustomed to my presence, perhaps allowing it to “hide” under debris before carefully removing its cover or even “trapping” it in a relatively confined area until it settles down enough to allow photographs. But nothing, not a single thing I tried, worked on this day. As it was through much of July and early August, temperatures were extreme—already well into the 90s despite my mid-morning arrival. Combined with the wide open spaces and a blazing hot sun, the beetles were already extremely active and very wary. The sandbar itself offered little help in corralling the beetles—stark, barren, devoid of any debris or other potential shelters that could be used to my advantage. Stubbornness prevented me from accepting this fact, so I spent the good part of two hours slowly stalking each beetle that looked like it might cooperate, only to have it fly before I could even get down on all fours or, once I did, run incessantly to the point that it was almost impossible to settle it in the frame—much less compose a decent closeup shot. Eventually I decided that the only way I was going to get a beetle standing still in the frame with any degree of closeness was to approach it from the front and try to catch it in one of its intermittent “stilting/sun facing” poses—a thermoregulatory behavior that tiger beetles employ when the sun heats the soil surface to temperatures that would be lethal for many other insects. The first shot in this post is the best of that type that I could manage (although I like its composition very much—I just wish I’d been able to get some closer shots as well).

The ”C”-shaped humeral lunule identifies this individual as Cicindela repanda.

As suggested above, C. repanda and C. hirticollis are quite similar in appearance, and at least in Missouri the latter is always found in association with the former, though only in wet sand habitats along the big rivers and not nearly in the same numbers as C. repanda. Until one develops a feeling based on “gestalt” it can be difficult to pick out individuals of C. hirticollis amongst the commoner C. repanda. I’ve already mentioned their slightly huskier build and somewhat bolder white markings, and C. hirticollis also tends to exhibit a slightly more coppery cast to the body. The surest character to use, however, is the “G”-shaped humeral lunule, which is the white marking on the “shoulders” of the elytra just behind the pronotum. The posterior portion of this marking is nearly transverse and usually angles sharply anteriorly on its inner edge. By contrast, in C. repanda this marking is always “C”-shaped and never curls forward on its inner edge. These characters can be compared in the lateral profile photos of the two species above and below (though not as closely as I would like).

The ”G”-shaped humeral lunule identifies this individual as Cicindela hirticollis.

I should mention that there was one other big river specialty species present on the sandbar—Ellipsoptera cuprascens (Coppery Tiger Beetle). I saw only a few individuals of this species and couldn’t get close enough to one of them to even fire off a single shot. For this species, however, I still had one more trick up my sleeve that allowed me to photograph it to my heart’s content (no, not capturing one and confining it in a terrarium!)…

REFERENCE:

MacRae, T. C., C. R. Brown and K. Fothergill. 2011. Distribution, seasonal occurrence and conservation status of Cylindera (s. str.) cursitans (LeConte) (Coleoptera: Cicindelidae) in Missouri.  CICINDELA 43(3):59–74.

Copyright © Ted C. MacRae 2012

A non-black background is better… often!

/ Ted C. MacRae / 2 Comments

In my previous post, A black background is better… sometimes, I came to the defense of the oft-maligned pitch black background. Some macrophotographers studiously avoid black backgrounds (BBs), claiming that they look ‘unnatural’. However, as I discussed in my previous post, there are situations—primarily with light-colored or translucent subjects or those that are seen only at night—where BB can be aesthetically pleasing or more consistent with the subject’s natural history (or both, as in the case of the subject of my last post). On  the other hand I do agree that BBs are overused, showing up in many photos where a non-black background would have been a better choice. The reason for this is simple—BBs are easy! All one must do is ensure that the area behind the subject is clear of light-reflecting objects. While this is certainly preferable over cluttered backgrounds with random leaves, branches, grass stems, etc. that distract from the subject, a BB may nevertheless not be the most aesthetically pleasing  choice for the photo (I am guilty of this myself). Non-black backgrounds, on the other hand, require more forethought, not only about what color to use and how to achieve it, but also regarding camera and flash settings which can be a bit trickier due to the fact that both background and subject must be properly exposed.

Argiope argentata (silvery argiope) | Santa Fe Province, Argentina

Choice of background to a large degree reflects the style of the photographer. Some may choose a particular color based purely on aesthetics, but as an in situ macrophotographer I prefer backgrounds that are consistent with the natural history of the subject—diffuse green for subjects typically seen on foliage, gray or brown for those typically found crawling on trunks and branches, and sky blue for those found out in the open (e.g., perched atop flowers). Each of these backgrounds requires different technique, and this large orb weaver, Argiope argentata (silvery argiope), which I encountered in a corn field near Villa Cañas (Santa Fe Province, Argentina) back in April, is an example of the latter. In contrast to the strictly nocturnal orb weaver (Eriophora ravilla) in my previous post, this species and its congeners are commonly seen suspended on their webs in broad daylight. BB worked well with E. ravilla, but it would not be a good choice for A. argentata due to the large amount of dark coloring on the subject. More importantly, it contradicts this spider’s diurnal nature. I could have used natural light, but the sun was shining on the other side of the spider. However, this actually made it easier to achieve the blue sky background while illuminating the subject with flash. The large size of the spider (the body alone measured ~35 mm in length) put a lot of distance between the subject and the lens, which allowed the use of a larger aperture (f/10) with still acceptable depth-of-field. With a bright sky and the sun nearly behind the spider, I was able to keep a low sensitivity setting (ISO 100) to prevent graininess and a fast shutter speed (1/250 sec) to prevent motion blur. The slightly larger aperture was all that was needed to achieve a natural blue sky color in the background. More difficult was actually clearing the background between the spider and the sky, as the web was slung low amongst the tall corn plants. The series of photos below (click to enlarge) shows the results of my earlier attempts to photograph the spider; at first not thinking about the distracting corn plants, and then trying to avoid them by angling myself lower relative to the spider, which ultimately resulted in a bad angle on the spider:

I finally decided to just break over the offending corn plants (above the ears!) to clear the background and give me the angle that I preferred. After that I was able to snap away to my heart’s content. Here is a closer view of the spider:

Lastly, I show the following series of photos to demonstrate the dramatic effect that aperture can have on a blue sky background. If you have a bright sky and don’t need a lot of DOF (e.g., you have a large subject-to-lens distance or a small subject lying within a narrow plane), adjusting the aperture up or down is a great way to achieve the precise color of blue desired. Larger apertures (lower f values) will result in a paler blue color, while smaller apertures (higher f values) create a deeper blue. In the photos below (click to enlarge), flash and camera settings are the same as those mentioned above except aperture: f/10 (left), f/13 (center) and f/16 (right).

Copyright © Ted C. MacRae 2012