Wednesday, August 17, 2005
ARGIOPE GARDEN SPIDER
We found this Cool garden spider last night while working in the garden. Here is some info about it:
Summer belongs to the flower spider, but fall belongs to the garden spider. At least fall seems to be when they are most prominent,cobwebs dripping with morning dew, huge bodies lurking in wait. There are many different species of web-spinning spiders in the garden, but two common species are the European garden spider (Araneus diadematus) and the Argiope garden spider. The European garden spider is characterized by its large tan/gray body with mottled tan/brown markings across the back, highlighted by five or more large white dots forming a cross. The Argiope is yellow or black with two rows of three white spots along its back; the Argiope is noted by its habit of spinning zig-zag webbing across the center of its web.
The garden spiders weave large flat webs suspended between plants, across paths, along window and door frames. They are generally found outdoors, although they may find their way indoors as fall progresses to winter. The European garden spider tends to preferwooded and shrubby areas, while the Argiope prefers sunny areas around houses and tall grasses. (Most of the web-spinners I have found in my garden are European garden spiders.)
We generally first notice garden spiders in late summer or early autumn in their adult stage. It is at this time that the spiders are largest, and the webs are outlined by mist from morning fog or dew. The eggs are laid in autumn in a silken cocoon, usually a dirty yellow or off-white, somewhat flattened mass, about one inch long, fastened under leaves, flowerpots, in nooks and crannies, any secluded and sheltered spot. As winter approaches, the adult spider dies, and the cocoon protects the eggs until late spring. In late May to early June, the cocoon releases hundreds, as many as 600-800, tiny golden spiderlings that cling together in a mass. If disturbed, the many spiderlings scatter, or drop, spinning "safety lines," until they touch ground and scurry for cover. After a few days, the mass of spiderlings scatter, each seeking a site where it can spin a small, irregular web about 2 inches across. As summer progresses, the females grow faster than the males, and as late summer approaches, the growth accelerates, and the females make larger webs, up to two feet across. The spiders have been around all summer, but only in late summer and fall do the large webs appear. Most adults die with the first frost, with the remainder dying by late November.
Although spiders can be cannibalistic, the practice of the female spider eating the male after mating is comparatively rare among garden spiders. It has been found that male garden spiders often mate with several females, and more often die from starvation and exhaustion, since they spend little effort feeding while searching for females.
The most noticeable habit of the garden spider is its web spinning. Some species construct the webs in the evening and take them down at dawn, hiding in nearby foliage, but the European garden spider constructs its web just before sunrise, and the spider is often found during the day, resting head down in the center of its web. If the web becomes damaged, the spider will eat it to preserve protein, and begin a new one. Although the structure of a web may be used for more than one day, the sticky threads need to be replaced daily because they lose their stickiness.
The web is started with a horizontal thread stretched between two supports. The spider lets out a thread that is carried to another support by a breeze or air current. The spider then pulls in the excess to stretch the thread taut. The spider crosses, laying down stronger thread. Then it crosses again, laying out a loose thread. The spider then moves to the center of the sagging, loose thread, and drops, letting out another thread and forming a ‘Y’. This ‘Y’ becomes the first three of as many as 50 radii. (The number of radii is consistent among members of the same species, but differs between species.) The spider walks out a radius, spinning out a thread. When the spider reaches the anchor point, it walks down the support to affix the new thread to another support point. The spider will spin threads between anchor points to give the web a frame to which other radii can be attached.
Once the frame and radii are in place, the spider then builds a small platform at the hub, from which a temporary spiral scaffolding works out to the edge of the web. Once the scaffolding is in place, the spider walks on the non-sticky scaffolding, from the outer edge to the center, attaching sticky threads that form the trap. The spider cuts away the non-sticky scaffolding as it progresses toward the center. The whole process of building a web takes about a half hour.
The thread is produced from a group of spinnerets located on the underside tip of the abdomen. The spider uses its rear legs to pull and stretch the coagulated silk from the spinnerets. The pulling acts somewhat like a taffy pull to strengthen the silk.
Garden spiders have poor eyesight, and generally detect prey by vibrations. They also generally have difficulty walking on anything other than their silk.
The garden spider eats whatever blunders into its web. The spider detects vibrations in the web from the captured insect’s struggles. Seizing the prey, the spider injects a poison that paralyzes and begins to liquefy the insect’s contents. At the same time, the spider wraps the prey in a shroud of silk. The hind legs pull out silk from the spinnerets and fasten the silk to the insect’s body while the front legs turn and spin the prey. Some garden spiders will then attach the encased insect to the web; others will carry it to the edge of the web and secure it there. Later, the spider returns and, with its fangs, sucks out the liquefied contents of the body. The empty shell is then cut out of the web and allowed to drop to the ground.
Weather is the worst enemy, especially drought and excessive rain. Many birds feed on garden spiders, as do some parasitic wasps and ants. No control on the part of humans is necessary, unless the spiders find their way into greenhouses, sheds or houses. The most effective control is cleaning up debris that would shelter the cocoons. If a chemical treatment is necessary, pyrethrins are effective for quick knock-down, with little residual effect. If a longer residual effect is desired, diazinon, chlorpyrifos (Dursban), or carbaryl (Sevin) can be used.
Good Guy. Although the garden spider does not discriminate between beneficial and pest insects, the number of winged pests outnumber the beneficials. Captured pests include moths, sawflies, whiteflies, horntails, craneflies, and mosquitoes.