Orb-Weaver Spiders

SCIENTIFIC NAME

Family Araneidae

APPEARANCE

The orb weaver spider group is comprised of a large number of species thus making it difficult to distinguish them from other spider groups and from each other. In fact, the Orb-weaver spider family, Araneidae, is one of the most variable in size and appearance of all spider families. However, the most observable appearance of orb weavers isn’t necessarily their appearance, but the appearance of the large webs they create. In general, orb weavers construct organized, circular grid webs that are similar in shape to webs depicted in Halloween decorations. More specifically, orb weaver webs are made of radial strands of silk that look like the spokes of a wheel with the spokes connected by numerous concentric circular silk strands. The web of the garden orb weaver spider is very large and can measure up to three feet in diameter. When observed in their natural habitats, orb weavers will usually be seen hanging head down in their web.

Like all other spiders, orb weavers have a cephalothorax (a fused-together head and thorax), abdomen, 8 legs and fang-like mouthparts called chelicera. Many orb weavers are brightly colored, have hairy or spiny legs and a relatively large abdomen that overlaps the back edge of the cephalothorax. Abdomens vary between species. Some orb-weaver spiders have spiny, smooth, or irregularly shaped abdomens. Most nocturnal orb weavers are usually brown or gray in color. Diurnal species exhibit bright colors of yellow or orange along with black markings.

BEHAVIOR, DIET AND HABITS

Orb weavers are typically nocturnal spiders and many species will build or do repair work on their webs at night. Some orb weaver spiders tear down and even consume much of the web’s silk as the morning begins to dawn. This interesting habit is performed in order take in moisture from dew that may have settled on the web and to prevent large animals such as birds from getting caught in the web.

Since orb weavers are not hunters or wanderers, they will sit in their web or perhaps move off their web and wait for prey to get tangled in their web. Should the spider move off the web, it will remain nearby and hidden in a protected site such as some rolled up leaves or on the branch of a plant. However, the spider remains aware of prey that may become trapped in the web by a trap line of silk that will vibrate and alert the spider if something enters the web. If a prey insect is trapped in the web, the trap line vibrates notifying the spider rush to the web, bite and paralyze the prey and wrap it in silk for later consumption. If something non-eatable is trapped, the spider will either just ignore it or remove it from the web and go back to its protected hiding place. Orb weavers are most often noticed by homeowners in the late summer and fall since the adult spiders have attained their largest size and have constructed the largest number of webs.

Small insects such as flies, moths, beetles, wasps and mosquitoes are examples of insects that make up the spider’s diet. Some of the larger orb weavers may also trap and eat small frogs and humming birds should they venture into the web. Orb weavers tend to inhabit locations where there is abundant prey and structures that can support their web. Typical habitats include areas around night-lights, tree branches, tall grass, weeds, fences, walls and bushes.

REPRODUCTION

Male orb weavers are much smaller than females and the male’s role in to mate with the female. Since the males are small, it is not uncommon for them to become the female’s first meal after mating. Female orb weavers produce one or more egg sacs and each sac may contain up to several hundred eggs.

SIGNS OF AN INFESTATION

Presence of the web is the most obvious sign of an orb weaver population

DISTRIBUTION

Orb weavers are found throughout the world, except for the Arctic and Antarctica. In North America, there are approximately 180 species of orb weaver spiders.

MORE INFORMATION

Despite their large size and fearsome appearance, orb weavers are not considered to be medically important. Orb weavers rarely bite and only do so when threatened and unable to escape. If bitten by an orb weaver, the bite and injected venom is comparable to that of a bee sting, with no long-term implications unless the bite victim happens to be hyper-allergic to the venom.

Preventing orb weaver spiders is usually unnecessary unless an orb weaver builds a web in a location frequented by people, in which case someone could be adversely affected by arachnophobia, the extreme fear of spiders. Some key preventive things a homeowner can do is reduce the population of insects that serve as food for spiders, seal up holes, cracks and gaps in the home’s exterior to prevent entrance by spiders into the home’s living spaces and remove ground litter and other sites that serve as spider harborage. Should the homeowner need assistance in control of these or any other spiders, contact your pest management professional (PMP) and request an inspection. Your PMP can then use his inspection findings to prepare a comprehensive pest management plan that will effectively and efficiently deal with the specific pest problem.

Spiders in the family, Uloboridae, commonly known as the hackle-band orb weavers are unique since they do not possess venom, the only family of spiders in the United States with this characteristic.