|Black and Yellow Garden Spider – Argiope aurantia |
Also commonly called black and yellow Argiope, banana spider.
Live spiders photographed at Georgia and northern Illinois.
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This sexually mature female Argiope has reached her maximum size, about 15mm (spiders are measured by body length).
Female Argiope are the largest spiders most people in the USA ever encounter. These charming creatures can be found in gardens and weedy fields from early summer to mid-Autumn, but females become conspicuous in their large webs only toward the end of summer. They can be extremely numerous in small areas, making walking difficult without disturbing them.
Argiope females lay eggs in egg sacs attached to low foliage. The eggs hatch in early summer, and the spiderlings disperse. Spiders grow in increments – being encased as they are inside a hard and rigid exoskeleton, they cannot grow unless they shed the old armor in a process called molting, much as snakes and other animals.
The timing of the molt depends on many factors, including the ambient temperature, the amount of food and water available, even the length of the day. Only after the final molt does the spider become a sexually mature individual. 
Call me crazy, but I thoroughly enjoy the gruesome spectacle of one of these majestic creatures capturing an insect in their large orb-web. I have been known to throw in a grasshopper or two just for grins. (Hey, you feed your dog, right?)
The large females sit head-downward in the center of their orb, unlike many of their kin, who sit hidden at the outside of the web, with a claw placed strategically on one of the highly-tensioned signal lines; when something disturbs the web, those spiders can sense the size and nature of the creature causing the disturbance without revealing themselves.
Not so with our gal Argiope (pronounced "are-JY-oh-pee"). She sits right out in the open. However, her cryptic camouflage makes her maddeningly invisible – so invisible, in fact, that they have taken to adding heavy, zig-zag silk to the web, so-called "stabilimenta" (it was once thought these structures added stability to the web) in order to prevent birds and other large creatures (men) from blundering into it and destroying the very metabolically expensive household.
In any event, the spider will rush to the prey and quickly throw silk over it to pin its appendages and reduce the chances of herself being bitten or stung; she then bites the prey in order to quickly paralyze it, and continues to wrap the now completely immobile and helpless creature, to be eaten later. Frequently you will see a few of thes coccooned insects hanging around – fresh food whenever she wants a snack or a meal. No refrigeration needed!
Stabilimenta are conspicuous lines or spirals of silk, included by many diurnal spiders at the center of their otherwise cryptic webs. It has been shown spider webs using stabilimenta catch, on average, 34% fewer insects than those without. However, webs with the easily-visible markings are damaged far less frequently by birds flying through them. It is an evolutionary tradeoff the spider can influence every time it builds a new web. The inclusion of stabilimenta is influenced by many factors, including prey density and web location. Read the study at Behavioral Ecology magazine.
The nature of these mysterious structures once led men to call these lovely beasts "writing" spiders.
Extreme closeup: spider's ventral abdomen and spinnerets
North American Insects & Spiders
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