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 FLORIDA SPIDERS
A source for information on spiders

 Spiny-backed Orb Weaver Spider  Gasteracantha spp.

Spinybacked orb weaver spiders are members of a large group of spiders.  They get the name “spinybacked” from the spines that stick out of the abdomen. They get the name “orb weaver” from the shape of the web that the female spider makes.

These spiders are common in yards, in gardens, and on porches and patios. They are not considered dangerous. They are actually beneficial because they eat insects like flies and mosquitoes.

The spinybacked orb weaver spiders are smaller than many other orb weaver spiders. The female’s body is about ⅜” long, while the male’s is 1/16” to 1/8” long. They are brightly colored spiders. The abdomen can be white, yellow, or orange.  There are red markings on the abdomen. The legs are black.

Spiny Orb Weaver Illustration
Spinybacked Orb Weaver Spider

Many people call these spiders “crab spiders” because of their rather flat body with spines sticking out of the abdomen. There is actually another group of spiders that is called crab spiders. Other names for spinybacked orb weaver spiders are “crab-like orb weaver spiders” and “spiny orb weaver spiders”.

One of the most common spinybacked orb weavers is Gasteracantha cancriformis (L.). It is common across the southeast, the Gulf coast, and California. They live near wooded areas and in gardens.

The female spinybacked orb weaver makes a silken web. She builds the web in trees, shrubs, or on houses. The circular part of the web is usually 10” to 12” in diameter. Sometimes the web is near the ground. It is common to find these webs near the home, especially if the porch light stays on at night.

Spinyback Spider Web
Spinyback Spider Web

The female usually makes a new web every evening. There is a section of the web where she waits and a separate section for catching prey. She stays alone on the web. The male spider hangs on a single silken thread near the female’s web.

When an insect flies into the web, the female spider bites it to paralyze it. If it is a small insect, she may eat it on the spot. If it is a large insect, she may wrap it and eat it later.

The female produces an egg sac late in the summer or in the fall. If it is near winter, she attaches the eggs under a leaf and wraps them in silk. The male dies after mating. The female dies after producing the egg sac.

The spinybacked orb weaver spider does not usually enter homes. It is possible for people to bring them inside with potted plants. They are not aggressive spiders and do not bite people unless they are picked up. Since these are beneficial spiders, most people are glad to see them around the home. It is seldom necessary to kill these spiders.

Sometimes spinybacked orb weaver spiders make webs in inconvenient places, like around the doorway or at the garage door. If this becomes a problem, try turning off the outside light. If the light must be left on, consider changing the bulb to a yellow “bug light” bulb. This will cut down the number of flying insects that come to the light and the spider will probably move her web to another location. It is advisable to call pest control professionals for an inspection. They will be able to provide more suggestions for keeping the home pest free.

Size:

The body is ½-inch or less in length.

Color:

A brightly colored spider that has a hard, white abdomen with red markings and black spines protruding from the edges.

Behavior:

The spiny-backed orb weaver spins flat, orb-shaped webs in shrubs, trees and in the corners of windows, soffits and similar outdoor areas of buildings. These spiders capture flying, and sometimes crawling, insects found around a home. They are not dangerous and would easily be overlooked if not for their unique coloration. They do not invade indoors unless carried inside while living in a potted plant.

This spider is common along the southeast coast of the United States and is a regular inhabitant of yards in Florida.

Control:

Spiny-backed orb weavers are not dangerous and are beneficial animals. They should not be killed if at all possible. In situations where numerous spiders are present, the webs can be regularly knocked down. Steps should then be taken to determine what conditions are attracting so many insects to a home where such a large number of spiders can feed. You may want to switch exterior light fixtures to yellow “bug” lights, which attract far fewer flying insects.

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