Silver garden spiders belong to the orb web-spinning group of spiders.

Silver Garden Spiders

by Cathryn Chaney

You won't find a silver garden spider (Argiope argentata) unless you live in the southern U.S. from Florida west through the Gulf Coast states and the southwest to southern California. Its range also extends south to northern South America. This large spider spins an orb web amid vegetation and catches a variety of insect prey. Look for it among shrubs, grasses and clumps of prickly pear cactus.

1. Spider Description

An adult female silver garden spider can be over 1/2 inch long, not counting her extended legs. The much smaller male spider has an adult body length of less than 2/10 of an inch and is less likely to be seen. Females are strikingly marked on the tops of their bodies with silver on the carapace and abdomen and two longitudinal bands of orange-brown toward the end of the abdomen. Two pairs of somewhat triangular projections stick out from the sides of the abdomen. The spider's underside is mostly dark-colored with yellow markings. The long legs are banded in black, yellow and brown.

2. Spider Webs

Like other orb-weaving spiders, the silver garden spider's web spans openings between vegetation where insects fly. Vertical spokes of framework silk radiate out from the center of the web, supported by interconnecting radial bands of silk, some of which are sticky to catch prey. Silver garden spiders construct areas of non-sticky web decorations toward the center of the web called stabilimenta. Young spiders make concentric rings and adult females make a cross-shaped pattern. It's not known exactly what function these have, but they may alert birds to the web presence so they don't fly into it. The devices may also help conceal the spider's presence when it is in position in the center of the web. Sometimes spiders build barrier webs in front of and behind the main web, probably for structural support.

3. Behavior

Silver garden spiders spend their days hanging head-downward from the underside of the middle of the web. It extends its legs two by two behind and ahead of its body in a cross-shaped pattern. The webs are usually placed low to the ground and tilted at an angle of 5 to 20 degrees from the vertical plane. The spider wraps captured insects in zig-zag bands of silk except for butterflies and moths, which it bites to subdue. Every two days, the spider tears down the web and weaves a new one, but it leaves up any barrier webs it has made.

4. Life Cycle

Female spiders are longer-lived than male spiders. They continue to molt and grow. Each newly molted spider is called an instar. Females are mature between instar 13 to 15. Males mature at instar 6 or 7. Not many female spiderlings survive to maturity, but most of the males do, and the female usually eats the male after mating. The female lays a mass of eggs in an irregularly shaped silken sac suspended by silk threads. Animals that eat silver garden spiders include different kinds of birds and lizards.

Photo Credits

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