Black and brown German Shepherd puppies

Fortunately, two things are in dog owners’ – and their dogs’ – favor. First, the bites of only two spiders in the United States typically can cause a reaction sufficient to warrant a trip to the veterinary clinic: the black widow and the brown recluse. Second, most dogs won’t have a problem after being pierced and injected with venom by either of these. Why some dogs do have serious reactions is unknown. It may depend on how much venom is injected, or it may be that dogs with compromised immune systems are more susceptible.

A third spider, the hobo spider, has not been officially identified as a threat to dogs. “There is essentially no information regarding hobo spiders in veterinary textbooks, ” Thoen says. However if you search the Internet, many suspected cases are mentioned. Again, because the type of bite can’t usually be identified, the dogs cited could have just as easily been bitten by a widow or recluse.

Thoen advises that a number of skin conditions, such as infections and cancer, may look similar to spider bites, and are much more common than a severe reaction to spider venom.

Where They Are
Black widow spiders are more plentiful in the southern and western U.S., but can be found throughout North America, according to the Centers for Disease Control and Prevention in Atlanta. The red or red-orange hourglass-shaped mark on their black, shiny abdomens makes black widows easy to identify, and they sometime have a bit of red on their “backs” as well. They like to make their sticky homes in places that aren’t often disturbed, such as under a house’s eaves, on fences and in woodpiles, according to the CDC, or in any kind of debris that’s allowed to pile up. Because they build webs between objects, bites “usually occur when humans come into direct contact with these webs, ” the CDC reports. Although a black widow leaves an obvious bite mark with two punctures on people, those typically are not easily found on a dog.

The brown recluse spider is, at its name implies, brown and lives mainly in the Midwest and South. It is sometimes called a “violin spider, ” because of the dark shape on its head that resembles a violin or fiddle. According to the CDC, brown recluses have six equal-sized eyes, while most spiders have eight. They tend to weave their webs in “secluded, dry, sheltered areas such as underneath structures logs, or in piles of rocks or leaves.” Indoors, a black recluse will build its web in a dark closet, in a shoe or in the attic. Unlike the black widow, the recluse requires pressure against its body to bite, according to the CDC. This pressure would be created, for example, if your dog happened to lie down on one, which, Thoen says, is usually how dogs get bitten by any spider.

According to the CDC, the hobo spider is most at home in the Pacific Northwest. Brown with a “distinct pattern of yellow markings” on its back, it’s a large spider without dark bands on its legs. Hobos’ webs are quite different from the widow’s or the recluse’s, being funnel-shaped and placed in holes, cracks and recesses. Outdoors, you’ll find them in “retaining walls, and in foundations, window wells, and stacks of firewood and bricks. Indoors, they can nest between boxes or other storage items, on window sills, under baseboard heaters or radiators, behind furniture, and in closets.” They run, rather than climb, and, the CDC reports that they are “much more likely to attack if provoked or threatened.”