Unless you live in the rainforests of South and Central America among the brightly colored tarantulas, it’s probable that any spiders you encounter will be brown or black. Although most are harmless to humans, America is home to a number of potentially dangerous spiders, making it essential to correctly identify a spider before handling it.
Consult a Spider Map
Knowing whether or not a species of spider is native to the area where you live will help you rule out a number of spider species. To the untrained eye, one brown spider may look pretty similar to the next, but with the guidance of a spider map, you’ll be able to take a pretty good guess at the likelihood that spider in your garage is a hobo or brown recluse.
Take a Photo
Unless you have nerves of steel or you’re a confident spider handler, you’ll probably be a little on edge around an unidentified spider. Take a snap of the spider on your cell phone, then examine the snap in the comfort of a spider-free environment. With the photo on your cell phone, you also have the option of uploading the photo to the Internet to assist with identification.
Gauge the Spider's Approximate Size
Never attempt to measure a live spider that is loose, especially if you suspect it may be a dangerous species. Either capture it humanely and safely using a spider catcher, or use a cell phone photograph for reference. If you can’t get an accurate estimate of the spider’s size from the photograph, use other items in the photo as a guide. For example, if the spider is photographed close to a light fitting, measure other light fittings in the house to get a maximum or minimum size. A pest control professional will be able to use descriptions such as "smaller than a quarter" as a guide for identifying a spider over the phone.
Observe the Markings
Some brown species of spider are so dark as to appear brown, so going off color alone is not always a good method of correctly identifying a spider. Black widow spiders have distinctive red, hourglass markings on their backs. Brown recluse spiders have a violin-shaped marking on their back, but this is not unique to them. But if you spot a six-eyed spider that is brown and has a violin marking on its back, there’s a good chance you’ve got a brown recluse on your hands.
Look for Other Clues
Often it is easier to identify a spider through its eggs or web. For example, the brown recluse weaves conspicuous webs that are often hidden, so if you spot a similar-looking spider next to a web, it’s probable that it isn’t a brown recluse. The eggs are often a dead giveaway, too. Brown widow spider eggs have distinctive spines, black widow eggs are smooth.
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