BigBuild: 2013

Another interesting creature found in my garden ..... black-and-yellow argiope spider (Argiope aurantia).

This is quite attractive and one of our more conspicuous species of orb weaving spiders. Orb web means it spins a web like a circle. The species name "aurantia" comes from medieval Latin “aurantium” meaning “orange (the fruit)”. Other commonly used names for this spider are golden orb-weaver, yellow garden orb-weaver and the writing spider. The black-and-yellow argiope breeds once a year. Adult males roam in search of potential mates. When they find a female, they build a small web with a white zigzag band across the middle either nearby or in an outlying part of the female's web. Potential males court by plucking and vibrating her web.

After mating, each female produces one or more (usually no more than three) brown, papery egg sacs. They are round in shape and up to an inch wide—each containing 300 to 1,400 eggs. The female attaches her egg sacs to one side of her web, close to her resting position at the center, since suspending the cocoon is particularly effective against ant predation. The multi-layered wall of the cocoon provides barriers against burrowing larvae of insect predators, though some wasps and flies lay their eggs in A. aurantia egg cases.

One study found that in addition to A. aurantia, 19 species of insects and 11 species of spiders emerged from A. aurantia egg cases. The vast majority, however, are eventually damaged by birds. In areas with a cold winter, the eggs hatch in the late summer or autumn, but the hatchling spiders become dormant and do not leave the egg sac until the following spring. Spiderlings generally resemble small adults. Once they mature, males leave their webs and wander in search of females. Female spiders are much larger than males, growing almost from 3/4" to 1 1/8". Males grow between 1/4" to 3/8". Both spiders have a cephalothorax (small front body section) covered with short, silvery hairs. The shiny, egg-shaped abdomen has yellow or orange coloring on a black background. The black-and-yellow argiope’s legs are black, with red or yellow bands.

Like other orbweavers, each leg has 3 claws per foot, one more than most spiders. Orbweavers use this third claw to help handle the threads while spinning. Predicated upon climate, these spiders may live a little over a year from their hatching in the fall until the first hard frost the following year. In warmer temperatures, the female may live for several years but males usually die after mating in their first year.

These spiders prefer sunny places with little or no wind to build their webs. Once they find suitable sites, they will stay there unless the web is frequently disturbed, or they can't catch enough food. Black-and-yellow argiope spiders often construct and repair their webs after dark. Their orb webs can be up to 2 feet in diameter and are very complex. To start the web, a black-and-yellow argiope firmly grasps a grass stem or window frame. The female then lifts her abdomen and emits several strands of silk from her spinnerets that merge into one thread. The free end of the thread drifts until it touches the substrate. Next she makes bridge lines and other scaffolding to help her build the framework of her web. She creates a hub with threads similar to spokes of a wheel. She switches to a sticky silk for the threads spiraling around this hub, which actually catches her prey. This process may take several hours to complete. When finished, a black-and-yellow argiope female eats the temporary scaffolding and the center hub. The spiders often add stabilimenta, or heavy zigzagging areas, to their webs. The stabilimenta resembles writing, hence one of their common names. The purpose of web stabilimenta is unknown, though some believe it may attract prey, provide structural stability, or prevent birds from flying through the webs. What is known is that only spiders that are active in daytime use stabilimenta.

A. aurantia is most active during the day. They are carnivorous predators, attacking flying insects that get trapped in its web. Their orb web captures aphids, flies, grasshoppers, mosquitoes, wasps and bees. The female spider hangs, head down, in the center of its web while waiting. Often she holds her legs together in pairs so that it looks as if there are only four of them. When an insect hits the web, the spider feels the vibrations and comes running. Occasionally, you may see her hiding off to the side with a thin silk thread attached to her web, which quivers when prey lands in it. (A female black-and-yellow argiope will eat a tasty item up to twice her size.) As is the case for all spiders, A. aurantia has a venomous bite that paralyzes its prey. The venom also digests the prey's body contents in order for the spider to ingest. These spiders have relatively poor vision, but are quite sensitive to vibration and air currents. When disturbed, the spider might first vibrate the web in an attempt to make itself seem bigger. Failing that, the black-and-yellow argiope drops to the ground and hides. The list of prey for this serviceably beneficial includes mosquitoes, moths and other flying insects including some species of wasps (especially mud daubers). Although people are concerned about being bitten by the A. aurantia, they are not dangerous. They may bite when harassed but it is no worse or harmful than a bee sting to a healthy adult. (The very young and very elderly in addition to individuals with compromised immune systems should exercise care or be supervised in areas where spiders are an issue.) The black and yellow garden spiders and other types of orbweavers are generally harmless but can be a nuisance when they build large webs in places inconvenient for humans. They are very beneficial to our environment and quite attractive—unless the mere sight of a spider triggers a case of arachnophobia!