Leetle bitty spiders, Part 5

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:

Leetle bitty spiders, part 4: Hentzia sp.

One of the more interesting "free-range" groups of spiders is the family Salticidae, the jumping spiders. They have one pair of marvelously large eyes situated prominently up front, which is what provides them the depth perception they need to coordinate their incredible jumping ability. They use this ability to leap from point to point to capture their prey and to get around from one plant to another. One day as I was out taking my routine census of the wild lime bush in the back yard, I noticed that two adjacent leaflets had been sort of stuck together. Now, whenever you notice something like that, you have to get your camera out to see if you can find out what did it. It could be a lepidopteran larva just taking a nap or getting ready to pupate; it could be a spider setting a trap; or it could b something else. In this case, it was a small (teeny, maybe 5 mm long) jumping spider in the genus Hentzia. There are five species in the continental United States, with only four in Florida: H. palmarum, H. mitrata, H. grenada, and a south Florida specialty (for the U.S., at least; it's also found in the Bahamas and on Cuba) is H. chekika. This particular spider looks like this: You can see the large eyes that are characteristic of all salticids, and you can see the body shape that is characteristic of the genus Hentzia: "somewhat elongate," according to the last revision of the genus, from 1989. If you want to get technical about it, here are some more precise characteristics as noted by Richman:
The genus Hentzia is here defined by the presence of both pencils of hair below the posterior median eyes and spatulate hairs on the ventral retromargin of the first patella and distal femur. These characteristics are most pronounced in the female, especially in regard to the hair pencils. Males often have elongated chelicerae and somewhat elongate bodies.
These spiders have a circum-Caribbean distribution, and most of the different species are presumed to have resulted from island speciation (the tendency of isolated breeding populations of a once-more-widespread species to develop unique traits that define it as a separate species). Although there are only a few species from which to choose, I was unable to take a photograph that showed sufficient detail to place the spider to the species level, but I'm happy to know that it's a Hentzia. Here is what I believe to be the egg sac of this same (or perhaps another) individual; it gives its location away by the way the adjacent leaves stick together: And today as I was tending the firebush (sadly, the scale saga continues) I noticed a tiny creature scuttle from the top of the leaf to the side away from me. Curious, I flipped the leaf over and snapped a few pictures; it was so small I didn't have any idea what I'd found. But it turns out to have been one very happy Hentzia (presumed) spider:

Leetle bitty spiders? Nunh-uh! Argiope species in Florida yards

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: These are not small spiders; this one is at least half an inch long, but remember, spider measurements exclude the leg length. If you add in the legs, it's two inches across; if you add in the "stabilimenta" woven into the web, the visual impression of this spider is daunting, indeed. Here's a picture of one of the business ends, the spinnerets on the abdomen: The liquid silk that flows from the silk glands hardens very soon after flowing through these nozzles; it's the various chemical constituency of the silk combined with the treatment it receives post-spinneret that determines whether it's "sticky" (viscid) or not. The function of the stabilimentum isn't known for certain, but some experiments show that birds are slightly better at avoiding webs with stabilimenta than those without. And a bird flying into the web, rather than being a tasty prey item for this spider, just means that she has to rebuild her web. Back in 1982, entomologist Thomas Eisner and ornithologist Steven Nowicki tested that hypothesis at Archbold Biological Station in central Florida demonstrating that before dawn, when birds are not yet active, both marked and unmarked webs survive at equal rates: about 80%. But after dawn, the unmarked webs started disappearing, until by noon only 8 percent of them remained, while fully 60 percent of the marked ones, those with "stabilimenta," remained intact. And while they had only one data point of a bird flying into a web (an Eastern Towhee encountering an unmarked web), it remains the most convincing explanation of the function of this visual marker. The other type of Argiope spider I found in my garden was actually photographed last year, in December, but I didn't realize what it was until I tried to determine for sure what today's photos (of A. argentata) were. Argiope florida looks pretty similar to A. argentata, but the abdomen of the latter has a golden back end with a few (6, in this case, although that might be variable) silver triangles there, while the former has three long projections of silver along its back half, as you can see in the fuzzy photo below:
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:
  1. 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)
  2. bird avoidance (the conclusion reached by Eisner and Nowicki)
  3. insect attractant
  4. camouflage for the spider itself (the conclusion favored by Marshall and Edwards, according to "recent research")
Whatever the case, the debate is fun, and so is finding and photographing these wonderful animals. References Eisner, T. 2003. For Love of Insects. Cambridge, MA: Belknap/Harvard. Marshall, S., & G.B. Edwards. 2008 Florida's Fabulous Spiders, 4th ed. Hawaiian Gardens, CA: World Publications.

Leetle bitty spiders, part 3: Crab spider sp.

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: This image is magnified probably 6x-7x (based on how it appears on my screen; if you click on it for the larger version, it'll jump up to about 10x or 11x). The spider is only about 6 mm from stem to stern(spiders are measured without their legs because of the extreme variability in leg length among species). Each leaflet in the background (remember, Wild Lime has pinnately compound leaves, which means each of those "leaves" is actually a leaflet) is less than 1/4-inch across. Here are a couple that didn't turn out too horribly: This unidentified spider has all the hallmarks of the family Thomisidae, crab spiders (that is, the true crab spiders, as opposed to the so-called crab spiders like the spiny-backed orb weavers): a flattened shape (not as flat as Selenopidae, but still), front two pairs of legs much longer than back two pairs (and those two front pairs of roughly equal length, unlike the "running" crab spiders, Philodromidae, in which the second pair is significantly longer than the first). Now, since no one has been able to identify the spider for me beyond the family level, I would normally have just left it there, and not posted about it here on the blog. But the next day, as I was out searching for yet another spider in this shrubbery (a jumping spider, subject of a post in the near future) I found something I hadn't expected to see. It turned out that the jumping spider I was hunting had moved and left no forwarding address, so I couldn't get any more pictures of it. After that, I turned to trying to find this little yellow crab spider again or, barring that, at least taking a census of the caterpillars whose eggs I'd missed. While I was doing that, I noticed a fairly good-sized caterpillar hanging from the underside of a leaf; most uncaterpillarlike behavior, at least for a young one that isn't trying to pupate. And lo and behold, that lil' larva was in the grip of that very same unidentified yellow crab spider I'd found the day before. Nature, red in tooth and claw, indeed! It seems that the number of invertebrate species that use Wild Lime is practically off the charts. Giant swallowtail butterflies lay eggs on it; their larvae eat it; ants patrol it; crab and jumping spiders prey on the ants and the caterpillars; dragonflies perch on it; orbweavers use it as support for their webs. The list goes on (probably, but I don't have the photos of it yet)! I'm no longer sure that I need to continue removing swallowtail eggs to protect this little plant; it seems that the spiders and other predators here are doing a fine job protecting it for me! Doesn't s/he look happy with that great big meal to digest?

Leetle bitty spiders, part 2: Selenops sp.

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: I took a few photos of it and posted them to bugguide.net, and fairly shortly thereafter received word that it was a spider in the genus Selenops, family Selenopidae, commonly known as "the flatties." As you know if you've read the first part of this miniseries on spiders, the eye arrangement is often critical to placing the spider even to the family level. And this family, as the etymological explanation on bugguide attests, is actually named after its eye arrangement:
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: And dorsal, with ruler for scale: The flattened aspect of the spider's body obviously enables it to squeeze into smaller nooks and crannies than its more round-bodied brethren; beyond that, it makes it look über-cool. Despite their rather fearsome appearance, their fangs are too small and their venom too weak to pose much more than an annoyance to people. So, hooray for the eyes of the moon!

Leetle bitty spiders, part 1: Allocylosa bifurca

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: But after hours and hours in the place, the attention of its adult visitors tends to wander. And when it wanders to the view through a few of the windows, that visitor might be able to see, not just what's outside the window, but what's "on" the window. A rather unusual-looking greenish-whitish transclucentish spider: Her "knobby" abdomen might remind you of the spiny-backed orbweavers (the so-called crab spiders, as distinct from the true crab spiders). For example, Gasteracantha cancriformis has spikes on her abdomen as well: But the abdomen of the spider pictured ends in sort of a "fishtail" arrangement that tells you right away that she's no "crab" spider. Her taxonomic name is Allocyclosa bifurca, and not only does she have an unusual appearance but she also has an unusual web-building habit, and one that makes her web conspicuous to a distracted museum-goer: she makes a unique "stabilimentum" in her web by weaving her egg sacs in a vertical line above her body, and her discarded meals in a line below her, as described on Bugguide.net and illustrated below the quote:
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.
As you can see, this individual has probably had quite a few meals that don't show up in her trashpile; I doubt that she was able to produce so many egg sacs from that one bit of discarded prey hanging beneath her... Here's a better picture of her web: I say "her" because the males of this species are so rare that 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:
1 2