Spinybacked Orb Weaver Spiders
Spinybacked orb weaver spiders (Gasteracantha cancriformis) 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 across the Southeast, the Gulf coast, and California. They are not considered a medically threatening spider. 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 7 mm long and 12 mm wide, while the male’s is about half the size. They are brightly colored spiders. The abdomen can be white, yellow or orange. There are red markings on the abdomen. The legs are black.
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.”
The female spinybacked orb weaver makes a silken web. She builds the web in trees, shrubs or on houses. 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.
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. She attaches the eggs under a leaf and wraps them in silk. The female dies after producing the egg sac.
The spinybacked orb weaver spider does not usually enter homes on its own. 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 management professionals for an inspection. They will be able to provide more suggestions for keeping pests out of the home.