When you think of a spider, you probably picture a big, round web with its resident spider poised in the center, waiting for a hapless fly to land in the web's sticky strands. With few exceptions, you would be thinking of an orb weaver spider of the family Araneidae. The orb weavers are one of the three largest spider groups.
The family Araneidae is diverse; orb weavers vary in colors, sizes, and shapes. The webs of orb weavers consist of radial strands, like spokes of a wheel, and concentric circles. Most orb weavers build their webs vertically, attaching them to branches, stems, or manmade structures. Araneidae webs may be quite large, spanning several feet in width.
All members of the family Araneidae possess eight similar eyes, arranged in two rows of four eyes each. Despite this, they have rather poor eyesight and rely on vibrations within the web to alert them to meals. Orb weavers have four to six spinnerets, from which they produce strands of silk. Many orb weavers are brightly colored, and have hairy or spiny legs.
Like all spiders, orb weavers are carnivores. They feed primarily on insects and other small organisms entrapped in their sticky webs. Some larger orb weavers may even consume hummingbirds or frogs they’ve successfully ensnared.
Male orb weavers occupy most of their time with finding a mate. Most males are much smaller than females, and after mating may become her next meal. The female waits on or near her web, letting the males come to her. She lays eggs in clutches of several hundred, encased in a sac. In areas with cold winters, the female orb weaver will lay a large clutch in the fall and wrap it in thick silk. She will die when the first frost arrives, leaving her babies to hatch in the spring. Orb weavers live one to two years, on average.
Special Adaptations and Defenses:
The orb weaver's web is a masterful creation, designed to ensnare meals efficiently. The spokes of the web are primarily non-sticky silk, and serve as walkways for the spider to move about the web. The circular strands do the dirty work. Insects become stuck to the these sticky threads on contact.
Most orb weavers are nocturnal. During daylight hours, the spider may retreat to a nearby branch or leaf, but will spin a trapline from the web. Any slight vibration of the web will travel down the trapline, alerting her to a potential catch. The orb weaver possesses venom, which she uses to immobilize her prey.
When threatened by people or most anything larger than herself, an orb weaver's first response is to flee. Rarely, if handled, will she bite; when she does, the bite is mild.
Range and Distribution:
Orb weaver spiders live throughout the world, with the exceptions of the Arctic and Antarctic regions. In North America, there are approximately 180 species of orb weavers. Worldwide, arachnologists describe over 3,500 species in the family Araneidae.