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Spiny Orb Weaver, a.k.a. Crab Spiders

Spiders are creepy. No getting around that. But some are so distinctive that many of us can repress the shivers long enough to appreciate their unique beauty and important function as eaters of pests. The Spiny Orb-Weaver (Gasteracantha cancriformis) is one of these.

Known in my neck of the woods as “Crab Spiders”, these little guys belong to the third largest family of spiders and have cousins all over the world (Australia has a particularly colorful genus, Austracantha, whose species come in practically every color and pattern imaginable). In the U.S, our natives can be found in all southern states from California to North Carolina. They are particularly common in the Gulf South region and in Florida; where they are often found in citrus trees and groves. Other common hangouts are brushy gardens and lightly wooded areas.

The coloration of the species can range a bit. The carapace, the hard upper shell, can be white, yellow, or orange and their spikes are predominantly black or red.

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Underside of the Spiny Orb-Weaver (note the small tufted silk in the web; a unique characteristic of the web of this species)

The females spin neat spiral wheel-shaped webs; with the circular strands containing the sticky capture silk.Tufts of silk, like tiny little spots of pulled cotton are unique features of their webs (see above). Some research suggest that these make the web easier to see for birds, thus saving the spiders rebuilding times, as wayward feathered friends often fly through, and destroy, spider webs.  The webs also contain larger areas of thick foundation silk (see below).

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Spiny Orb-Weaver rebuilding a web. Foundation silk can be seen in the web.

The webs feature an open area in the center where she typically brings her prey to feed (after biting them to liquefy their insides of course). Smaller insects don’t require wrapping, but prey larger than the spider are typically wrapped before being transported to the central area.

The males hang from threads of silk nearby the females, but don’t spin large webs of their own. In the winter, they will attempt to mate with the females by first tapping on the web and then, once he’s got her attention, climbing  warily onto her web.The males are much smaller than the females and can easily become dinner. Mating takes place over a span of a half hour or more, after which, the male attaches a thread from her web.

Unfortunately, both male and female Spiny Orb-Weavers die shortly after mating. The males live for another 6 days or so; while females live slightly longer. She lays 100-260 eggs in a crafted egg sac that she wraps in multiple layers of silk. Once completed, she leaves her web for the last time and attaches the eggs (typically) to a nearby leaf. Once she completes this task, she dies.

FAQ:

Q: Do crab spiders bite? Are they poisonous?

A: They can bite, but they are not poisonous and the bite is not considered medically significant. Their spikes, though can break the skin. Because of this, they are considered a nuisance species during the harvest season in citrus groves and in garden settings.

Q: We call some other critters crab spiders. Are they related to these?

A: Probablt not. There are several types of spider referred to colloquially as “crab spiders”, but you are likely referring to members of the family Thomisidae.

Memebers of this family are ambush predators and don’t spin webs like the orb-weavers. They also have a very different appearance and earn their crabby nickname because of how they position their front pair of legs and how they can scuttle sideways. They are quite colorful and diverse critters in their own right and deserve their own post; which I will write soon.

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Goldenrod “crab” spider (Misumena vatia) …not “our” crab spiders

Sources:

http://aggie-horticulture.tamu.edu/galveston/beneficials/beneficial-23_spiny_orb_weaver_spider.htm

http://animaldiversity.org/accounts/Gasteracantha_cancriformis/

Photo – (Goldenrod “crab” spider) © Grzegorz Gust | Dreamstime.com – Misumena vatia

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