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")