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Crevice spiders and black widows

March 31, 2017
By CHARLES SOBCZAK - Local Living , Cape Coral Daily Breeze

Crevice spiders

(Family Filistatidae)

Next to the housekeeper, the crevice spider is possibly the second most common spider found on the islands and around Southwest Florida. It is especially fond of older wooden structures where it builds its unmistakable nest under floor joists, next to light fixtures or on the corner of windows where it can prey upon insects that are attracted to the house lights at night.

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Crevice spiders
(Family Filistatidae)
Other names: southern house spider, crevice weaver
Status: FL=common
Life span: to 8 years
Length: 1.2-2 in. (30-50 mm)
Reproduces in finely woven webs that all have a narrow tunnel wherein the spiders hide and raise their brood
Found: Throughout garages and storage rooms in Southwest Florida

Crevice spiders do utilize their sheet-like web to trap and entangle their prey. When a moth or fly becomes caught up in this wooly silk (cribellate silk) the large, dark brown spider rushes out and subdues its victim with its fangs, quickly injecting a venom into the insect to subdue it. Bites to humans, though very rare, are not life threatening and the swelling seldom lasts for more than a few days.

The crevice spider, because of its unsightly nests, is not as welcome into peoples homes as is the housekeeper. After time, their silken webs become hosts to dead flies, wasps, moths and other insects and the spider itself is dark and foreboding. By and large however, crevice spiders do more good than they do harm, killing stinging hornets, black widows and cockroaches. They in turn are eaten by geckos, anoles, small rodents and a handful of birds willing to take them on.

Black widow

(Latrodectus mactans)

This is the one spider you probably do not want to look for. Females are aggressive and will inject potentially lethal neurotoxic venom into the bite that can result in death. Sixty-three confirmed deaths were reported in the United States between 1950 and 1959. Improvements in anti-venom have significantly reduced this mortality rate but the black widow, worldwide, is considered to be one of the most dangerous spiders on earth. They are easy to recognize by their shiny black bodies and distinctive red hourglass markings on their rounded abdomen.

The female black widow is aptly named. The local species, Latrodectus mactans, is the only known black widow that practices sexual cannibalism. Shortly after the male mates with the female, she turns on him, killing him with her powerful venom, and then consumes him. Not all pairings result in this bizarre ending, and males that manage to escape can go on to fertilize other black widows, if they dare!

Female black widows are very fertile, laying four to nine egg sacs per year with each sac containing up to 400 eggs. In keeping with the temperament of their mother, the juvenile spiders practice paternal cannibalism and only a few of them make it to maturity. Black widows feed on woodlice, other spiders and a wide variety of insects. They are in turn preyed upon by preying mantis, spider wasps and a number of specialized flies. If you happen across a black widow do not attempt to pick it up or get too near it. They are fast and aggressive and if you are bitten by one you must seek medical attention immediately!

This is an excerpt from "Living Sanibel - A Nature Guide to Sanibel & Captiva Islands" by Charles Sobczak. The book is available at all the Sanibel/Captiva island bookstores, Baileys, Jerry's and your favorite online sites.



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