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I browsed the web hoping to learn more about black widows and hopefully, find some safe ways to get rid of them. We don't use pesticides.
I learned black widows are nocturnal, preferring the cool and darkness to daylight. They come out at night to hang in their webs and feed. Turning on outdoor lights at night attracts bugs and these bugs are what widows like to eat. Keep the lights off at night or get yellow lights, which don't attract bugs.
Widows spend the day in dark places. They hide under boxes, cabinets, garbage cans, wood piles, rocks, outdoor furniture, water meters, etc. It's best to keep these things far away from your house.
You can identify the black widow's web if you look closely. They are small webs with a thick 'den' in the center usually very close to the ground. The female spiders will hide inside the den during the daytime, emerging at night to sit in the center of their webs. Once you see one, you will be able to identify them. Anyway, if you see this web, the spider is nearby.
Smash (don't spray) the spider. If you kill one, be absolutely sure to destroy the egg as well.
A number of things are recommended for getting rid of them. The most successful seems to be to go hunting for them at night with a flashlight. If you locate one, use a stick to squish it against the side of it's hiding place and then do your best to remove the hiding place altogether so no more take it's place.
Other things were suggested like vinegar, eucalyptus and sticky fly paper traps.
This was the best advice site I found on getting rid of Black Widows: How to Get Rid of Black Widows - The column on the right had lots of good "Natural" suggestions.