On a cool day in early Fall there was reduced insect activity, but I amused myself by watching the large number of spiders that have spun their webs in our marshlands. The main spiders suspended upside-down on their webs were banded garden spiders (Argiope trifasciata ). These close relatives of the better-known golden garden spider ( Argiope aurantia ) not only have a different coloration, but their web lacks the familiar zig-zag pattern called a stabilimentum. The purpose of this distinctive silken structure remains obscure, but it has been suggested to possibly attract insects to the web, and/or to warn birds from flying into the web and destroying it. Banded garden spiders place their webs fairly close to vegetation, tilt it slightly away from the vertical, and hang on the back of the web. Thus they are somewhat protected from bird attacks; they responded to my movements by shaking the web, and one book reported that the females will drop to the ground when disturbed. These large orb-weaving spiders have a defensive problem in that they position themselves openly on a web to catch prey during daytime, and thus make themselves available to avian predators. They are brightly colored on their ventral surfaces with two bright yellow stripes on either side of the reddish spinnerets. Could these vertically oriented stripes be designed as camouflage or just the opposite, to advertise the presence of a large, conspicuous spider that can defend itself?
An exciting battle was underway in one web where a banded garden spider had captured a bumblebee as large as itself, and was quickly rolling it up in strands of silk from its spinnerets. Within a minute or two the bumblebee had succeeded in escaping from its silken shroud (see photo), wrestled a bit with the spider and then flew away and began foraging in the adjacent jewelweed flowers. It is remarkable that the spider would be willing or able to cope with such fierce prey which is so well defended. Perhaps the risk for such a large food item is worth the danger?
It is remarkable if somewhat sad that the hundreds of spiders in our marsh will soon be dead after frost occurs. The species will be carried on by eggs sealed in cocoons during the winter.
As I looked down on the ground I noticed another fierce arachnid hunter, in this case a grass spider ( Agelenopsis sp.) with very long spinnerets at the rear of the body (see photo). This spider resembles a wolf spider in that it hunts by leaping on prey, but it builds a sheet-like web with a retreat where it hides while waiting. The web is not sticky as is the case with the orb weavers. Most true wolf spiders make very little use of webs to catch prey and hunt by running along the ground. It is very interesting that the character most specific to all spiders (ability to spin silk) varies so much among different groups, depending on their modes of prey capture.
These three spiders would be good species to learn since they are quite likely to be encountered in the eastern US. Spiders are ecologically very important and can be quite interesting if we can get past the arachnophobia yuck factor. I recently purchased two useful guidebooks (Spiders of the Eastern US by Howell and Jenkins; Spiders of the Carolinas by Gaddy) and I admit to a certain creepy feeling while reading through the book and looking at the pictures.
Bill Dunson, Englewood, FL & Galax, VA