As summer winds down, so do the lives of most insects and invertebrates. Among the more conspicuous is the striking black-and-yellow garden spider. It's a big, colorful and common orb-weaving spider whose circular webs I often find in overgrown fields.
Orb-weavers begin their sophisticated webs by establishing a bridge from one anchor to another. From a twig or grass stem, for example, the spider releases a strand of silk from its several pairs of silk-making organs called spinnerets. The breeze catches the strand and carries it until it touches another perch and the bridge is formed.
After strengthening the bridge by moving across it several times and laying down more layers of silk, the spider drops from a strand fastened to the center of the bridge. It repeats this process a number of times in all directions until there are a series of strands radiating outward from the central hub. Then the spider adds an outward spiral to complete the web. Spider silk is strong, elastic, and sticky -- perfect for snaring unwitting prey. But maintaining a functional web requires almost daily attention.
Look closely, and you'll often find a heavy zigzag or crosshatch pattern near the center of the web. This is a lure that attracts unsuspecting insect prey. These distinctive patterns are made of silk that reflects ultraviolet light. The rest of the webs spiral and radiating strands lack this quality.
Prey is attracted to the UV reflection because many pollen and nectar laden flowers also reflect UV light. Insect pollinators can see UV light and are thus duped into investigating the web's reflectivity. After they land on the web, it's too late. They become caught on the sticky invisible strands, and the vibrations caused by their thrashing alerts the web weaver that dinner is served.
Soon female garden spiders will mate and lay up to 1,000 eggs in a papery egg sac which is attached to the edge of the web. After laying eggs, the females die. The eggs hatch before winter arrives, but the spiderlings remain in the protective sac until spring. Then the tiny spiders drop to the ground to begin a new generation.
First Published: September 13, 2009, 8:00 a.m.
