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: 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!
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: 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: 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,
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: 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? 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):Here's another view, where you can see the unusual shape of the abdomen: The arrow-shaped posterior makes it look a bit like
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.)
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: 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. bug-collecting kit with soft forceps; it might be about time to invest in one.)
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: 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): 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:
I never finished the miniseries I had started last December on spiders found in and around my yard; here is the fourth installment, starring two species of orbweaver that are commonly encountered in gardens both in Florida and elsewhere. They are so common, in fact, that they have common names, unlike the vast majority of spiders: Argiope argentata is known as Silver Garden Orbweaver or Silver Argiope, while A. florida is known as the Florida argiope. Florida has two other Argiope species, A. aurantia and A. trifasciata, but I have yet to encounter them in my Florida back yard, so today's post is just about "known species" to me. One of the reasons I leave my Florida yard a bit unkempt is so that spiders, those efficient and abundant predators, can have more time to control any bad bugs that might be around. A neat and trim yard, with a beautiful lawn and well-defined flower beds and no overgrown bunch grasses or wildflower beds is one that requires chemical control of harmful insects (which also "controls" beneficial ones), and dozens of hours of mowing, weeding, trimming, clipping, hedging, and weed-whacking. I try to think that it's not just my own laziness that urges me instead to let nature take her course. Instead, it's principle: I do what I can to maintain a semblance of ecology in my garden (a la Grissell's idea of garden ecology). If said principle happens to result in less "work" for me, and more photographic and entomological opportunities, well, so be it. So that's why I haven't yet trimmed my muhly grass, despite the fact that its stalks and blooms are yellow, not purple, and why I've left the "weedy" species (Bidens alba, Richardia grandiflora, etc.) around the fences unwhacked: these "unsightly" areas of overgrowth allow many more hiding places for insects, and attachment sites for spiderwebs. And as a result I've got literally dozens of spiders (Argiope species, Leucauge species, Gasteracantha species, and more) helping me control the flies and other annoyances that might otherwise rise to "treatment required" levels. Here, though, without further ado, are the pictures of the two Argiope spiders. A. argentata, the more commonly encountered spider, first:
This image shows a relatively small individual that I found in my front courtyard, and it was in a relatively inaccessible location, so the photograph isn't perfect. Had I realized how relatively rare it is in my yard, though, I'd have made sure to make some better pictures of her. As it is, this is the only individual of A. florida that I know I've encountered here; all the others (and there are nearly a dozen on the property right now, of varying sizes) are Silver Argiopes.
There is no stabilimentum present in the photo above, but the webs of all Argiope spiders usually do have them. While Eisner's experiment proved to his own satisfaction the function of the stabilimentum, other araneologists (specifically spider scientists; arachnologists study the class Arachnida, which includes, but is not limited to, spiders) are not as convinced. Marshall and Edwards, authors of Florida's Fabulous Spiders, review the four proposed functions as follows:
- as implied by the name, the stabilimentum strengthens or stabilizes the web (Eisner and Nowicki disproved this hypothesis by comparing the strength of de-stabilimentized webs (with their stabilimenta dissolved by alcohol) with those that still had them and finding no difference)
- bird avoidance (the conclusion reached by Eisner and Nowicki)
- insect attractant
- camouflage for the spider itself (the conclusion favored by Marshall and Edwards, according to "recent research")
I'm outside every chance I get, trying to investigate how my back yard functions. I check the light conditions at various times of day; I see who is visiting what plant and when (and if possible, why); and every now and then I get a picture that might serve as the basis of an ID, and I try to get it identified. That's where bugguide.net comes in. One of the reasons I like to use websites like bugguide.net is they are run by such a passionate crowd. These people love what they do, and it shows. They are amateurs in the truest sense of the word. They aren't paid to help people figure out what specific creepy crawly they have; they just like to do it! True, some people monetize the service; many's the field guide author who unashamedly asks these experts for help and then authors a field guide to, for example, moths of the northeast. But that's fine; in fact, it's an improvement on the days when this kind of specialized knowledge was locked up in the ivory tower, accessible only to those who made a pilgrimage to the hallowed halls of academe, or read their specialized journals at their library, or whatever. Of course, these people also run the risk of being given a bum steer; the people at bugguide are amateurs, and they make no bones about it. And, in the case of spider ID, they know the limitations of trying to ID an animal with only a picture. Often, it can't be done. A case in point: the other day I was out there inspecting my Zanthoxylum fagara for caterpillar damage. I'd recently had three or four Giant Swallowtail caterpillars using it as fuel for making Giant Swallowtail butterflies. That's fine, I thought. I love butterflies. But when I saw how much of this little plant they were able to defoliate, I had second thoughts. Since then, I've been removing butterfly eggs from the plant whenever I find them. I figure, if I miss a couple, it's my mistake, and I'll pay for it in Wild Lime defoliation. Fair enough. The game is afoot, and the plant is our playing field. But when you start investigating a plant for one form of invertebrate life, you often find others. For instance, as I was turning over the leaves (watch out for the thorns! it's not called lime prickly ash for nothing!) I nearly mistook this teeny yellow spider for a yellow butterfly egg. I was just about to remove it when to my great surprise, it moved! (My eyes must be getting old; the giant legs that are so prominent in the cropped image were invisible to me in the field—I only noticed them on the image after I downloaded it.) Being no dummy, I quickly realized that here was something I needed to take pictures of. But taking pictures of such a tiny creature is a bit of a guessing game; I have to just set the camera on manual focus and move the camera in and out until I think I've got a good shot:
If you're a regular reader of this blog, you know by now that I love my pool fence. I've gotten more good bugs on my pool fence than I have from any other single source on the homestead. But every now and then I have to venture inside the fence for some reason or other, even when, as now, it's no longer "swimming season" (defined as water temperature at or above 85°F). Usually these excursions intramuros are to retrieve some object Eric has thrown over the fence and NEEDS to have back in his hot little hands. Now, daddy, now NOW NOW! A couple of weeks ago, it was his kickboard. So I dutifully went behind the fence and did my little reach-out-and-grab-for-it-without-falling-into-the-pool-and-isn't-this-a-narrow-piece-of-deck-between-fence-and-water dance. And when I finally succeeded in fishing the kickboard out of the water, I found a curiously flattened (by nature, not by me) spider clinging to it:
Selenops is from Greek selene (σεληνη)- "moon" + ops (ωψ)- "eye, face". Latreille translated it into French as "yeux en croissant" which means "eyes in a crescent."That's right, this spider genus actually makes "moon eyes" at us! It wears a crescent moon on its face and in its binomial. Appropriate for an astronomer-turned-naturalist, no? Now back to our spider. Based on these photographs, this individual can only be identified to genus level; even with the fairly decent photos, it's simply too difficult to ID some spiders any further. And in this case, no one on bug guide was willing to ID this spider beyond the genus level. There are seven known species in the US, and many more tropical ones that could easily be imported to south Florida. And without dissecting the genitalia under a microscope, there's no way to be sure you've ID'ed it correctly. Furthermore, taxonomic work on the genus is ongoing; a recent paper revised the North American, Central American, and Caribbean members extensively. That paper also describes them as superlative spiders:
They are exceptional in that both their running and striking speeds place them amongst the world’s fastest animals (Crews et al. 2008), and they are extremely dorsoventrally flattened.Here are a couple more photos: Face-on:
I've seen estimates of spider density (the number of spiders in a given area) that range from 11,000 spiders per acre (in woodlands) to over 1 million (some estimates go as high as 2.5 million) per acre in a grassy field. Now that's a lot of spiders! Here at the homestead, I don't think we have quite so many. Oour 1/4-acre lot has its share, but I suspect that the combined footprint of the swimming pool and the house skew the numbers downward. Nevertheless, they are quite visible lately. The autumn months (even in the "autumn-less" land of Florida), particularly October and November, are when spiders are at their most conspicuous, and I sure have been seeing a lot lately. In fact, I have found over a half dozen different species that I haven't told you about before; enough to start a miniseries on spiders. If you don't know yet, let me tell you now, spider identification is for neither the faint-hearted nor the lightly-equipped naturalist. In order to identify all but the most conspicuous and common spiders correctly to the species level, you need a dissecting microscope or a very good macro lens and lots of luck. I make do with neither because, fortunately, for most people, including naturalists like me, identification to the family level is often "good enough." (I'm thinking of starting a new blog, "the lazy naturalist," but somehow I can never seem to find the time!) If you can get a photo that shows the eye arrangement well enough, your task is greatly eased, because each spider family (or subfamily) has a fairly distinct arrangement. It's not as foolproof as dissecting the genitalia, but it gets you as close as most people are willing to get... Once you've managed to narrow down your spider's ID to the family level, your location can narrow it down further, because there will usually be just a few species from which to choose in a given area, and odds are that your most common and conspicuous spiders will be fairly easy to identify (but, as this series of posts will show, it gets harder the closer you look). So, to inaugurate this little spider series, I propose an unusual spider that I found, not at the homestead proper, but at the Children's Museum a couple of blocks away. The museum is in a lovely historic home (built in 1912), white wood with green trim: It's kept up immaculately despite (and because of) the amount of kid traffic it receives. Inside, it has lots of toys, play scenarios, and what-do-you-call-em's to keep kids busy, like this ride-on airplane:
This orbweaver does an interesting thing in its web, which is rightfully referred to as protective mimicry. The egg sacs are attached to the web in a straight up vertical row and act as a sort of stabilimenta. And the discarded prey carcasses are kept the same way, except in a row straight down. The females perch in the center of the web in between the egg sacs and the carcasses and are difficult to make out since the spider and the egg sacs are both green and also similarly shaped.one arachnologist has even wondered aloud (and in print) whether the species is parthenogenic! This spider is typically found exactly where I found it at the museum: under the eaves of houses. The very first description of it, all the way back in 1887, was made from a spider found on the porch of a house on Merritt Island. (It also seems to be a Florida, or at least a southern, spider: the only two states with data points for it on bugguide.net are Florida and Texas.) I haven't found it on my homestead yet, but I will keep looking! The taxonomic name is fairly interesting: Allocyclosa means "like" or "similar to" Cyclosa, and in fact, this species used to be placed in that genus. The name Cyclosa means "to move in a circle, circling spider," which could fairly be applied to almost all orbweavers but, owing to the rules of taxonomy, is bestowed on this genus and no other. Spiders in both genera (Cyclosa and Allo-cyclosa) "have a well-known behavior of including prey remains and other debris in the stabilamenta of their orb-webs", but the webs I've seen of Cyclosa sp. include other kinds of detritus, while A. bifurca seems pretty stereotyped: egg sacs above, prey remains below. The genus name itself is of quite recent origin; Allocyclosa was created in 1999 on the basis of the phenotypic distinction between A. bifurca and every other spider in Cyclosa. The distinction is captured in the specific epithet: Bifurca means, of course, bifurcated, or forked, and, according to the namer (Levi, 1999), "Allocyclosa differs from Cyclosa by having the abdomen posteriorly vertically biforked." That is, it has a "fish-tailed" abdomen. Levi goes on to remark that "Both body shape and lightly sclerotized genitalia separate this species from Cyclosa. " You can see the former character best in the first image, above (click it for the larger version); since I don't have a dissecting microscope, a specimen, or the expertise to use them if I had them, I'll forgo showing you the lightly sclerotized genitalia, if you don't mind. I like this picture the best; you can actually see the arrangement of the eyes, and it looks like they're smiling:
One of the most familiar spiders to Florida residents is the spiny orb weaver, Gasteracantha cancriformis. You'll see people flailing their arms wildly after running into their webs all the time. This actually happened a lot at our old house, because these little guys make fairly large webs, and they loved to decorate our front porch back at the old house. They were so abundant in the fall that I'm tempted to call it our halloween spider; they might as well have been our trick-or-treat decorations. This fall, though, at the new place, they're a bit more scarce, although that might change soon, as you'll discover after reading this post. Just this morning I ran into one web while I was trimming the ficus hedge our next-door neighbor so thoughtfully installed between our two properties: