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:

Related Images: