Flower spiders: Thomisidae

There are many genera of crab spiders (also known as flower spiders) in the family Thomisidae. One of the more common in my yard is (I think) in the genus Mecaphesa (but here's a good illustration of why I'm not positive about the ID). Like most crab spiders, these have a very variable appearance. In fact, they are able to vary their appearance to match the background against which they appear; it takes a bit of processing to get them to show up well when they're photographed in situ. I've written about these spiders before, but I saw one the other day and happened to have my camera with me, so I thought I'd at least take a picture:
Crab spider. Boca Raton, FL, September 29, 2016.

Thomisid (crab) spider. Boca Raton, FL, September 29, 2016.

As you can infer from the photo, they're quite small; the dune sunflower that it's perched on is only a couple of inches across. Not a threat to humans, although it might provoke startlement and wonder from any who happen to notice the little feller. However, when we zoom in on their scale, they start to look a bit more daunting:
Thomisid spider, close-up. Boca Raton, FL, September 29, 2016.

Thomisid (crab) spider, close-up. Boca Raton, FL, September 29, 2016.

As you can see, their front two pairs of legs are MUCH longer than the middle or hind pair. These ambush predators rely on those long front legs to seize their prey rapidly, then they use their chelicerae (fangs) to inject venom to finish them off. According to the University of Kentucky web site about crab spiders,
Scientists think that the venom of certain crab spiders is more potent than that of most other spiders: this allows crab spiders to quickly paralyze the large and tough bees that often visit flowers.  However, crab spider venom is not known to be especially dangerous to humans.
In case you're wondering, the not "especially dangerous to humans" doesn't mean being bitten wouldn't hurt. It just means that you'll probably feel, at most, an "ouch!" and some slight muscle cramping (to paraphrase Rod Crawford's description of the typical response to Tarantula bites). This bears remembering. We live in such a sanitized world, so far removed from an everyday experience of nature, that any reminder of it (lizards, snakes, spiders), or even the possibility of slight discomfort caused by it, sends shudders of revulsion down our spines. Like any wild animal, spiders should be treated with caution and as much knowledge as we can bring to bear on them. The more we know about them, the less frightened of them we need to be. If you're a caterpillar, on the other hand, go ahead and be frightened. If you're not wary, you are in for a rough time, as this "orange dog" (Giant Swallowtail cat) found out a couple of years ago:

Know before you go! Disguises and chemical defenses and living on a spiny plant only take you so far in life...

Etymology It's entirely plausible that the name of this family of spiders derives from the Greek word thôminx, "string." The suffix -idae is the typical New Latin suffix appended to the name of any organism to indicate that it is belongs to that taxon. (For example, gulls are "larids," meaning they're in the family Laridae.) However, the Century Dictionary, my go-to dictionary for etymology, gives a slightly more interesting derivation from its definition of Thomisus (the original name of a genus of this family): whip, scourge! screen-shot-2016-09-30-at-10-52-43-am

Dewdrop spiders: kleptoparasites

A few months ago, I joined a Facebook group called Florida Entomology. It's nice to see so many different pictures of insects and spiders and whatnot from around the state. And several of the people who post there are incredible photographers. One recent post caught my eye, because it captured the incredible beauty of a tiny spider that I see relatively frequently in my yard: a kleptoparasitic (food-stealing) spider in the complex Argyrodes/Faiditus/Neospintharus/Rhomphaea. It was particularly interesting to me because just about 10 days earlier, I'd gotten my own first acceptable image of a dewdrop spider from my yard:
Dewdrop spider, sedis incertae. Presumably Argyrodes/Faiditus/Neospintharus/Rhomphaea. Boca Raton, FL, September 18. 2016.

Dewdrop spider, presumably Argyrodes/Faiditus/Neospintharus/Rhomphaea. Boca Raton, FL, September 18, 2016.

Just how small is it? Well, I have a particularly fine macro lens on my camera (this is my DSLR, not my phone), and I was about as close to the spider as I could get and still have it in focus (less than 20 inches). That means the image scale is as large as it can possibly be. If you click the image above, you'll get a file 1496 pixels wide. It makes it look huge. It's not. If that spider were next to a bee's head, it would fit on the eyes. The one from Steve Long's image (the Facebook post I referenced at the beginning of this post) is described as "one-third the size of a grain of rice." The largest ones I've seen are no bigger than their namesake:1 dewdrops. Spiders in this group live a particularly daring lifestyle: they live in the webs of larger spiders, eating the prey that its host doesn't want or isn't fast enough to get or vigilant enough in guarding. Marhsall and Edwards provide a good description of its behavior in Florida's Fabulous Spiders:
This species [Argyrodes nephilae] enjoys the very great advantage of not having to produce or maintain its own web. It actually avoids the main web of the host spider, preferring to hang out on the frame and barrier web strands. Here it waits until wrapped prey is unattended by the host spider. Then it stealthily sneaks up to the prey, dragging a line behind it which is attached to the barrier web line. Once it attaches its own line, it cuts the thread from which the prey hangs. The prey then swings out into the barrier web. If the Argyrodes has done its job well, the host spider will never know it has been robbed. But if the Argyrodes nephilae makes a mistake, the bigger spider will come charging over to reclaim its prize.
Etymology The spider discussed above specializes in living in the webs of one of our largest orbweavers, Nephila clavipes, about which I'm astonished to discover I've not written before on this site, except for in asides on other posts. I'll be sure to rectify that soon. In any case, that large spider, I presume, is where the specific epithet (nephilae) of its tiny kleptoparasite comes from. The genus name, Argyrodes, means "silvery." Speaking of silvery spiders, it's worth pointing out that members of this silvery dewdrop spider group don't live just with the yellow-silk orbweaver. They can also be found in the webs of the more common (in my yard) large orbweaver, the Silver Argiope (Argiope argentata), about which I've written in the past. Here is a shot taken last year that shows both species, so you can get an idea of the enormous size disparity between them:
Argyrodes sp. Boca Raton, FL, September 10, 2015.

Argyrodes sp. Boca Raton, FL, September 10, 2015.

The image above also shows why I haven't written about these little guys before: same lens, same photographer, different luck capturing an image of this little one. Here's a crop from the above photo showing just the argyrid:
Argyrodes sp. Boca Raton, Fl, September 10, 2015.

Argyrodes sp. Boca Raton, Fl, September 10, 2015.

No reason to write a post about that!

Step into my parlor…

...said the spider to the lady beetle. And yet, nothing happened. This morning before work I went out and, as usual, was taking pictures of whatever I could find in the yard. I found this lovely Southern Sprite damselfly (first of the season):
Southern Sprite (Nehalennia integricollis). Boca Raton, FL, May 8, 2015

Southern Sprite (Nehalennia integricollis). Boca Raton, FL, May 8, 2015

It's always a pleasure to see these relatively rare damselflies. (Odd, too, how abundance is so tied to locale: Everglades Spite (N. pallidula) is considered very rare, while Southern Sprite isn't, and yet I get dozens and dozens of the former over several months and very very few of the latter. I guess being near the Everglades is conducive to the occurrence of Everglades Sprite? While most people across the range of these insects are not near the glades...) When I was finished with the sprite's photo session I wandered over to the patch of dune sunflower I have growing along the drive. I noticed one flower had two petals sort of curved upward toward each other, indicating, most likely, the presence of a hunting spider. (That is, a spider that hunts without using a web.) It had tied the petals together with a strand of silk; you can see them curling up toward the camera in the photo below:
Thomisid spider waiting for breakfast. Boca Raton, FL, May 8, 2015.

Thomisid spider waiting for breakfast. Boca Raton, FL, May 8, 2015.

Thomisid spiders are commonly known as "crab spiders" (not to be confused with Gasteracantha cancriformis, commonly known in south Florida as a "crab spider," although most naturalists call it the spiny-backed orbweaver to avoid confusing it with the "true" crab spiders like the one above). The true crab spiders are so called because their front pairs of legs are drastically elongated, much like the pincers of a crab. It's one of the largest spider families, with over 2,000 species worldwide. There are at least 130 species in 9 genera in the United States, so identification to species level is left to the true spider experts, the araneologists (as distinct from the arachnidologists, who study arachnids in general, which includes arthropods from other orders such as scorpions, mites, ticks, and chiggers, in addition to the Daddy Longlegs, which aren't true spiders at all). While I was taking pictures of this unusual flower-trapping arrangement (normally I see the petals of the flowers curled down, rather than up), I noticed a wee little lady beetle about to become breakfast:
Lady beetle, meet spider. Boca Raton, FL. May 8, 2015.

Lady beetle, meet spider. Boca Raton, FL. May 8, 2015.

And then the strangest thing happened: the spider just remained motionless while the beetle climbed on the spider's back, tumbled off onto the disk portion of the flower, and then scurried away out of sight!
Let's make a closer acquaintance.

Let's make a closer acquaintance.

So long, and thanks for stopping by. (The beetle is visible to the lower left of the spider.)

So long, and thanks for stopping by. (The beetle is visible to the lower left of the spider.)

I wasn't able to snap a picture of the scene as the beetle left, but I was certainly surprised to see what I assumed would be a typical predation scenario turn into nothing at all. In case you're curious, the lady beetle looks very much like the "metallic blue" lady beetle, Curinus coeruleus, although it's by far the smallest one of them I've ever seen. References Marshall, S., & G.B. Edwards. 2008. Florida’s Fabulous Spiders, 4th ed. Hawaiian Gardens, CA: World Publications. Ubick, D., P. Paquin, P. E. Cushing, & V. Roth (eds.). 2005. Spiders of North America: An Identification Manual. Keene, NH: American Arachnological Society.

Dragonflies and damselflies returning to the yard

After a dry beginning to March (and no rain since then, but at least the heat's moderated a bit for the past few days), the odonates have started returning to the yard, just in time for the equinox! One or two of them run into mishaps:
Watch where you fly! Halloween Pennant (Celithemis eponina) served up for breakfast to a spiny-backed orb weaver (Gasteracantha cancriformis). Boca Raton, FL, March 18, 2015.

Watch where you fly! Halloween Pennant (Celithemis eponina) served up for breakfast to a spiny-backed orb weaver (Gasteracantha cancriformis). Boca Raton, FL, March 18, 2015.

but by and large they are still the most formidable airborne insect predators out there. Most of them sprint to safety as I approach, although the Blue Dasher is often more docile,
Blue Dasher (Pachydiplax longipennis). Boca Raton, FL, March 19, 2015.

Blue Dasher (Pachydiplax longipennis). Boca Raton, FL, March 19, 2015.

as is a chilly Eastern Pondhawk in the early morning:
Eastern Pondhawk (Erythemis simplicicollis). Boca Raton, FL, March 20, 2015.

Eastern Pondhawk (Erythemis simplicicollis). Boca Raton, FL, March 20, 2015.

The smaller and daintier damselflies are generally more approachable with a camera even after the sun has warmed them up a little; after the "chill" of the morning burns off, most of my dragonflies sprint away as I approach. Damselflies, on the other hand, sit still so you can sneak up on them. And, if you look at the bottom of the photo below, other creatures have little difficulty approaching as well.
Rambur's Forktail (Ischnura ramburii). Boca Raton, FL, March 20, 2015.

Rambur's Forktail (Ischnura ramburii). Boca Raton, FL, March 20, 2015.

Since I didn't notice the spider until after I'd come inside to view the photos on the screen, I have no idea what kind it is. Presumably a flower spider of some sort; it's quite small, given that the damselfly is no colossus itself. Happy first day of spring!

Damsels in Distress

You may remember that I volunteer with the Palm Beach County Department of Environmental Resource Management from time to time, helping them clean up and maintain the natural areas here in Boca Raton. Last weekend there was a work party at Yamato Scrub, and we were there for sunrise, coffee, donuts, muffins, and—oh, yeah—work. We trundled wheelbarrows full of sand from the sand mound to a few areas of sidewalk between the two recreated wetlands on the site. There’s a sand berm between the northern pond (the deep one) and the southern wetland (much larger and shallower). When the rains come, the sand next to the sidewalk tends to follow the water downhill, leaving the sidewalk higher and drier, which will eventually cause the sidewalk to fracture and degrade. So our work party helped to shore up the sand around the sidewalk, delaying the inevitable for another few seasons. We also did the traditional work party routine: trash pickup, with long-handled grabbers and trash bags, cleaning up as much of the area as we reasonably could. You always find the usual stuff that people discard (cans, bottles, wrappers, shotgun shells), but you're also always on the lookout for the fun stuff. For example, when we did the planted area in the parking lot, my covolunteer Dan found the weirdest object I’ve yet seen: a fully inflated toddler’s waterwing. What on earth was that doing in the parking lot of a scrub area? As we were taking trash from around the perimeter of the wetlands, we ran across some pretty blue flowers, which our ERM coordinator ID’ed for us as Blue Curls (Trichostema dichotomum); I was able to snap a decent image with my iPhone and its little Olloclip macro lens:  
Blue curls (Trichostema dichotomum</em.). Yamato Scrub, August 30, 2014.

Blue curls (Trichostema dichotomum

We also ran across some hogplum (Ximenia americana) in flower; the contrast between the delicate blooms and the long, wickedly sharp thorns, never ceases to impress me (particularly when I get too close!). I couldn't get good focus with the iPhone, so here's a shot from the next day with my real camera:
Hog plum (Ximenia americana). Yamato Scrub, August 31, 2014.

Hog plum (Ximenia americana). Yamato Scrub, August 31, 2014.

Of course, during a work party I can’t exactly tote around my real camera and rig, so the iPhone photos just serve to remind me of what’s there until I can get back to the site with my DSLR and its macro lens to do some real “work.” For example, here's a shot of the blue curls taken with my Nikon instead of my smartphone:
Blue curls (Trichostema dichotomum</em.). Yamato Scrub, August 31, 2014.

Blue curls (Trichostema dichotomum

Nice to get some focus across the entire image! In fact, the main reason I went back to the site the day after the work party was that while we were working, I noticed some damselflies that intrigued me—spreadwings of some sort, but without my macro lens, I wasn’t able to get a sharp enough picture to ID them. So I returned the next day with my real camera and set about hunting them down. Turns out I wasn’t the only hunter in the wetlands: this enterprising Rambur’s Forktail (Ischnura ramburii) captured an unwary (or just unlucky) Atlantic Bluet (Enallagma doubledayi).
Rambur's Forktail breaking its fast on Atlantic Bluet. Yamato Scrub, August 31, 2014.

Rambur's Forktail breaking its fast on Atlantic Bluet. Yamato Scrub, August 31, 2014.

Damsels in distress, indeed! The fork tail in the picture above is spreading its wings, but only to keep its balance and flight-readiness; when resting normally, it folds them over its back, like so:
Rambur's Forktail (Ischnura ramburii). Yamato Scrub, August 31, 2014.

Rambur's Forktail (Ischnura ramburii). Yamato Scrub, August 31, 2014.

Here's a closer look at her enjoying her breakfast:
Rambur's Forktail (Ischnura ramburii) and breakfast. Yamato Scrub, August 31, 2014.

Rambur's Forktail (Ischnura ramburii) and breakfast. Yamato Scrub, August 31, 2014.

After some hide and seek, I was able to relocate some of the spreadwings and, as I might have expected, they’re the only species we have here in Boca as far as I know: Carolina Spreadwing, Lestes vidua:
Carolina Spreadwing (Lestes vidua). Yamato Scrub, August 31, 2014.

Carolina Spreadwing (Lestes vidua). Yamato Scrub, August 31, 2014.

Carolina Spreadwing (Lestes vidua). Yamato Scrub, August 31, 2014.

Carolina Spreadwing (Lestes vidua). Yamato Scrub, August 31, 2014.

But when you're intent on hunting down one particular insect, there might be others who are just as intently trying to hunt you down!
Biting fly, Tabanid family. Yamato Scrub, August 31, 2014.

Biting fly, Tabanid family. Yamato Scrub, August 31, 2014.

A word of caution if you plan to hang out in the wetlands: there are plenty of predators on the wing! For example, a few dragonflies (top, Little Blue Dragonlet, Erythrodiplax minuscula; Middle, Common Green Darner (Anax junius); bottom, unidentified. Erythrodiplax_minuscula_YS_20140831 Anax_junius_YS_20140831 Dragonfly_YS_20140831 And if you're the first one on the trail, you might find a few roadblocks put up by other kinds of predators, like this spider (I think it's the tropical orb weaver, Eriophora ravilla, but I'm not sure):
Orb weaver. Yamato Scrub, August 31, 2014.

Orb weaver. Yamato Scrub, August 31, 2014.

You need to look sharp if you don't want to walk out of the scrub wearing spider silk! Now, if only those biting flies had been the bugs that these spiders were eating... Oh, well.

New backyard spider: Cyrtophora citricola

Gardeners in south Florida are the inverse of the typical beachgoer: instead of looking forward to a sunny day for reading, we look forward to a cloudy morning for weeding! August days, even in the morning, can be brutal. Earlier this week my weather station reported a heat index of 110°F! So when we get rain overnight followed by lingering clouds, we jump at the chance to get a bit muddy while trimming back the overgrown foliage and pulling out the weeds from the flower beds. When we get the chance to do this, we often discover new and unusual things, like this spider:
Cyrtophora citricola. Boca Raton, FL, July 29, 2014.

Cyrtophora citricola. Boca Raton, FL, July 29, 2014.

Here's another view, where you can see the unusual shape of the abdomen:
Cyrtophora citricola</eM. Boca Raton, FL, July 29, 2014.

Cyrtophora citricola, Boca Raton, FL, July 29, 2014

The arrow-shaped posterior makes it look a bit like another spider I’d found in the past, the trashline orbweaver, but instead of being in a typical orb-shaped web, it was in the middle of the craziest web I’d ever seen, draped all over one of my small silver buttonwoods. The web was roughly spherical, but nowhere near as organized as a funnel web, and it was made of dry, not sticky, silk. Here's a shot from the UF/IFAS featured creatures website—can you find the orb in that mess?
Colony of Cyrtophora citricola filling space between palm leaves. Photograph by G.B. Edwards, Division of Plant Industry, Florida Department of Agriculture and Consumer Services.

Colony of Cyrtophora citricola filling space between palm leaves. Photograph by G.B. Edwards, Division of Plant Industry, Florida Department of Agriculture and Consumer Services.

Turns out the web belongs to Cyrtophora citricola, a tropical tentweb orbweaver. This is an old world species introduced to Florida in the Miami area around this most recent turn of the century—at least, it was first written up in 2000; see summary by Edwards (2006). Here is the first description of their arrival in Florida (Halbert 2000):
Cyrtophora n. sp., a spider: Several specimens have been collected in webs in Ficus benjamina at a nursery in Homestead (Miami-Dade County; E2000-545; Duraid I. Hanna; 2 March 2000, and E2000-965; Julieta Brambila;12 April 2000). Cyrtophora species are orbweaving spiders that make a lot of barrier webbing in addition to the orb. The barrier web tends to collect a lot of plant debris. The spiders appear to hide in or near the tip of a curled leaf and look like a piece of dead leaf or other detritus. The webs are about the dimension and volume of a basketball. If numerous, their webs could be conspicuous features in the landscape, and could possibly be considered a nuisance by some homeowners. NEW UNITED STATES RECORD.
These are interesting spiders, classed as orbweavers despite the fact that they produce a very large tent-like structure of nonsticky silk in addition to their horizontal rather than vertical orb-shaped web. (Most people encountering their crazy tentlike web have trouble even locating the orb in the middle of all that 3D craziness!) Here are some fun facts about these little critters:
  • They are colonial, often establishing large living aggregations with dozens to scores of square meters of web; this large coverage enables them to overcome the disadvantage of nonsticky silk.
  • They have rather oddly shaped bodies, with a trademark look to their rear end: a “horizontally oriented bifurcation at the posterior of the abdomen,” as Edwards (2006) puts it.
  • Like Allocyclosa bifurca, the only other spider in Florida that it resembles in any way, shape, or form, C. citricola webs arrange eggs and detritus in a characteristic “trashline.” (I find it very interesting that the two “spiky orbweavers with bifurcated posteriors” in Florida share this behavioral trait in addition to their morphological similarity.)
Etymology Cyrto- means humpback or hunchback; phor means thief, while phoras means fruitful, bearing. Not entirely sure which meaning Forsskål had in mind when he named the species in 1775 (posthumous publication arranged by his colleague Niebuhr). Citricola, it seems clear, is for the citrus trees where presumably the first specimens were found. References Edwards, G. B. 2006. Cyrtophora citricola (Araneae: Araneidae), a Colonial Tentweb Orbweaver Established in Florida. Entomology Circular No. 411 Fla. Dept. of Agriculture & Consumer Serv. Mar/Apr 2006 Division of Plant Industry. Halbert SE. 2000. Arthropod Detection. Florida Department of Agriculture and Consumer Services, Division of Plant Industry, Tri-ology 39(2): 7.  

Dune sunflowers, spiders, and moths, oh my!

Dune sunflower, Helianthus debilis, is a commonly recommended plant for Florida native gardeners. It's in the daisy family (Asteraceae), and it's very pretty:
Dune Sunflower (Helianthus debilis). Boca Raton, FL, July 9, 2012.

Dune Sunflower (Helianthus debilis). Boca Raton, FL, July 9, 2012.

Yellow rays, purple disc flowers, loads of pollen—very attractive to bees and butterflies.
Halictid bee on Dune Sunflower. Boca Raton, FL, May 26, 2013.

Halictid bee on Dune Sunflower. Boca Raton, FL, May 26, 2013.

It self-sows and reseeds annually, so once you've got it established, you don't have to do much except remove it from places you don't want it! It grows best in "dune" environments: sandy areas in full sun, hence the common name.   Since it grows to cover such a large area (it's often used as a groundcover), it naturally develops a bit of an ecosystem of its own. I'll frequently find flower spiders gleaning insects attracted by the bright colors and abundant pollen. Until the other day, though, I hadn't thought of it as a larval host plant for lepidoptera young, but now I've seen a couple of things that have started me thinking. For example, here's a flower crab spider (family Thomisidae, species incertae, most likely Mecaphesa celer, formerly known as Misumenops celer) enjoying a fly of some kind (order Diptera, perhaps family Sarcophagidae, but without a view of the head, it's hard for a nonspecialist like me even to get to the family level on this one!):
Flower spider with fly. Boca Raton, FL, June 13, 2013.

Flower spider with fly. Boca Raton, FL, June 13, 2013.

But here's another flower crab spider with what looks like a tiny caterpillar in its mouth:
Flower spider with caterpillar. Boca Raton, FL, June 13, 2013.

Flower spider with caterpillar. Boca Raton, FL, June 13, 2013.

If you're not convinced that there's a caterpillar there, here's a close-up:
Detail of flower spider w/caterpillar in Dune Sunflower.

Detail of flower spider w/caterpillar in Dune Sunflower.

Once I noticed that caterpillar, I started looking for more, and sure enough, these Dune Sunflowers appear to be some sort of host plant (maybe just a roosting location during the day?) for what look like grass-skipper or moth caterpillars. Here's one without a spider munching on it; it appears to be munching on the flower instead:
Caterpillar on Dune Sunflower. Boca Raton, FL, June 13, 2013.

Caterpillar on Dune Sunflower. Boca Raton, FL, June 13, 2013.

I haven't been able to find much on Helianthis debilis as a host plant for lepidopterans; according to the interwebs, its only attraction is as an adult nectar source. My Wagner, though, lists sunflower as the host plant for the common looper moth caterpillar, which this caterpillar resembles fairly closely (although it looks much MORE like the related soybean looper, which does not feed on sunflower, at least according to Wagner, and MOST like the found-in-Florida Cabbage Looper, Trichoplusia ni, which isn't specifically associated with sunflowers). So I'm going to tentatively ID it as Cabbage Looper, and if someone wants to tell me I'm wrong, I'm happy to listen. I don't think the caterpillar will mind, either way. References Wagner, D. (2005). Caterpillars of Eastern North America. Princeton UP.

New photos: Spiny-backed orbweaver

gasteracanthacancriformis_20121101
Tooling around the house in preparation for Halloween, I found this little lady near the ficus that our neighbor planted to mark the property line: She's a spiny-backed orbweaver, Gasteracantha cancriformis. I wrote about this species last year around this time (spiders are most numerous and visible in the fall), but I finally got a couple relatively decent pictures of one and wanted to show the world. I've been trying for some time now to get an image that shows this darn spider's eyes. I'm beginning to think I'll have to capture one and pose it, but that goes against my photography ethic: don't do anything that might cause distress to the subject (or the photographer)! (I don't have a bug-collecting kit with soft forceps; it might be about time to invest in one.)

Your eyes are like little moons… well, sort of.

selenops_detail_20121009
I've written about Selenops spiders before, but thought I'd give it another go, now that there's such a cooperative one living in a crack on the landing: Most spiders build webs, so they rely more on their sense of touch to sense the vibrations of prey that have become stuck in their traps. Other groups of spiders, though, like the jumping spiders (Salticidae) and the wolf spiders (Lycosidae) have excellent vision, because they rely on it not only for safe and effective locomotion but to capture their meals. As you might guess, web-building spiders have relatively small eyes, while jumping spiders and wolf spiders normally have at least one extra large pair among the eight eyes they typically carry. (For a comprehensive chart of spider eye arrangements, visit this page at bugguide.net.) Here's a typical jumping-spider eye: Notice how the eyes in the middle (the median eyes) are quite a bit larger than the next pair outboard, and there's another pair that stare straight sideways mounted a bit higher up on the head. This arrangement enables the jumping spider (typified here by the pantropical Menemerus bivittatus, or Gray Wall Jumper) to execute their unparalleled feats of precise acrobatic locomotion. The web-builders, on the other hand, generally have small, equal-sized eyes, like this friendly Eriophora ravilla I photographed last January: Spiders in the family Selenopidae, on the other hand, lie somewhere between these two groups. They don't build webs, but they hang out in crevices, between the glass and the mullion in your windowpane, and other such confined spaces, capturing prey by ambush. So their vision has to be pretty good, but they don't need the extraordinary depth perception of the jumping spider. And as you might expect, their eyes are somewhere in between the jumpers and the web-builders. They have four median eyes arranged in a semilunate arc (hence the allusion to the moon goddess, Selene, in their family and genus names), and two very large lateral eyes that presumably enable them to see quite well out the sides of their lair: Combine that with the rather fearsome-looking jaws (called chelicerae by araneologists) and you have a beast that, while probably quite beneficial to the average homeowner, is usually considered to be less than endearing.

Leetle bitty spiders, Part 5

menemerus_profile_20120219
Menemerus bivittatus, also known as the Gray Wall Jumper, is a pantropical species of jumping spider that occurs in four of the southern United States: Florida, Louisiana, Texas, and California (here's an image from Los Angeles that was posted to bugguide a couple of years ago). It's unclear (to me at least), why it has this disjunct distribution, but it was apparently introduced into Florida from the Old World tropics as far back as 1912. It is associated almost exclusively with human habitations. Based on a sample size of one (i.e., me), it seems that when a curious backyard naturalist (i.e., me) approaches it with a camera, it waves its chelicerae (the front "feet") in a warning fashion or threat display, although what kind of threat this 1-cm long arachnid with fangs too weak to penetrate human skin can pose is beyond me. Unfortunately, I wasn't able to capture this behavior with my camera; every shot I have shows her with her chelicerae demurely folded in front of her: One thing I discovered about this spider is that it has an incredibly quick reaction time to the flash of a digital camera. When I was taking these pictures, each time I clicked the shutter button while the spider was in one place, in perfect focus, but in the split second between when the flash fired and the exposure was made, the spider literally jumped to a different location. (I suppose the large eyes characteristic of the Salticidae, or jumping spiders, make it rather sensitive to bright lights!) It was quite a challenge to get any of the shots to come out in focus; I pretty much had to guess how far away and in what direction the spider would jump and prefocus in that general area. A few shots did come out, but I had hoped for far more interesting and diagnostic images, based on how docilely the spider let me approach, despite the foot-waving display. Oh, well. They didn't turn out too badly, I suppose. Like most spiders, despite the rather fearsome appearance, they are beneficial to humans on account of their diet. The UF "Featured Creatures" web page for this species mentions that
All free-living stages feed primarily on small Diptera which alight on buildings, although they are capable of capturing large crane flies twice their length, and larger, heavier muscoid flies.
For reference, here's a crane fly (with 64 North American genera and some 1600 species, family-level (Tipulidae) ID is all you can really get from a photograph):

Crane fly (Tipulidae family), Boca Raton, FL, February 15, 2012

The etymology of M. bivittatus was fun to figure out. The derivation of the genus name, which translates to something like "moon thigh," was a bit of a puzzle until I happened to turn to a book I don't own, but hope to some day:  Spiders of North America: An Identification Manual has as its 73rd and last chapter a magisterial etymological dictionary that is a model of scholarship. According to this work, it was Eugène Simon who, in 1868 at only 20 years old was not yet a master of Greek—but the first edition of his Arachnides de France had already been in print for 4 years!—who named this genus. The first part of the name, Menemerus, is supposed to come from the Greek mene, moon, but (had Simon mastered Greek more fully, as he did later in life) it should have ended in -s (menes). The second part of the name, -merus, is Greek for thigh. Apparently Simon meant the name to refer to the crescent-shaped "thigh" of the male palpal femur. The specific name, bivittatus, is a lot easier: Latin for two-striped (bi + vitta), referring to the stripes on the carapace, easily seen in this view:
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