Dish soap (dawn!) mixed with water, shaken in a spray bottle.
Call an exterminator
Get a pet lizard
Spiders live where the food is, you don't have a spider problem, you have a food problem. What insects are attracting the spiders? What is attracting the insects?
Maybe some borax around the house could deter the main sources of food
Close all windows and doors, set off the required amount of foggers and wait the recommended amount of time. Repeat again in a few weeks if needed. Most foggers/bug bombs work on most spiders and many are persistent over some time after application.
Use bug bomb(s) first to kill the existing spiders. Then apply permethrin diluted with water to a 0.5% solution, spraying at all entry paths to the garage, edges, and dark areas.
The idea is to not just prevent spiders from returning. It's also to deprive them of a reason to return by removing their food supply. Permethrin is a wide-spectrum insecticide and repellant. It has very low toxicity to humans, most mammals, and birds. Not good around cats or fish. It has good persistence (6-8 weeks).
I have no experience with black widows, but when I lived in rural Cambodia with its huge jumping spiders (they also have their egg sack hanging on their belly, so you really don't want to squash them) RAID seriously was my best friend and life saver.
Not all, but I couldn't say which ones were and were not. And some of them could seriously fuck you up. The house was wooden, so they always found a crack to squeeze through. But at least I didn't have scorpions like some of my colleagues.
If it were me, I would call an exterminator. Anything under $200 would be totally worth not having to deal with it and knowing that they'll take care of it better than I could.
Spiders in general is one thing, but a ton of black widows is something I wouldn't mess with. Those spiders could make you quite sick if not ending up in the hospital. Shieeeet. If you're of a vulnerable population like elderly, young, or already sick, they could kill you.
I’ve lived in a house that has a Black Widow problem for 14 years. I had severe arachnophobia when I moved here. Unfortunately, I don’t use poisons in my house, so my only option was to kill them by hand. The first several years, I would do regular patrols of my garage and yard at night to squish them. Night is the best time to kill them because they will usually sit in the middle of their nests. If they are not in the nest, I can usually find a bug to throw in the web that draws them out quickly. I had a favorite tool for the job, but anything screwdriver-ish will work. I know all their favorite spots, so it doesn’t take long to do a sweep. I also destroy the egg sacks.
I realize that without covering my house with poison, I will never be rid of them. More than anything, I just try to keep my floors and yard tidy with less spots for them to call home. Luckily, I have never seen one in the house other than a few juveniles. I think there is no food in the house for them, so the small ones that get in the house end up starving.
Most people go with poisons, so I thought I would pop in with my weirdness. Don’t worry about it too much. But also take precautions like not leaving your shoes where they could get in. And inspect boxes that have been in the garage before bringing into the house.
How many Widows we talking here? They’re common, but if you can see 10+ in one garage that sounds like an infestation you want dealt with professionally.
Permethrin. You should be able to get it at a Tractor Supply or Quality Farm & Fleet. Dilute it according to directions, or to about 10% overall concentration, put it in a sprayer, spray all around your garage. Follow all safety precautions, and wear googles and a respirator just to be safe. DO NOT allow any cats to come in contact with it until it fully dries; permethrin is very toxic to cats, but it should be fine once it's dry.
It will kill arthropods (spiders and insects), and acts as a fairly long-lasting repellent to prevent future infestations.
As someone else said, if you have a spider "problem", your real problem is that you have a lot of other insects that are acting as a food source for the spiders. Figure out what the other insect infestation is, fix taht, and you should fix your spider problem.
EDIT: black widow spiders aren't actually particularly dangerous to people. Most bites resolve themselves without any medical attention, and the very, very few fatalities are usually very young children, very old people, or people that are already very ill.
Well. You don't. OTOH, you can pre-treat clothing with a 5% permethrin solution, and that will keep arthropods away from you. You can safely treat pants, shirts, jackets, and socks, but should not treat underwear, gloves, hats, or balaclavas. Let it dry completely before wearing though.
Looks like it's also not great for steel, zinc, nylon, and some other stuff.
EDIT: Note that they were using 12,000 ppm for 1 hour to achieve 100% elimination of black widows. It sounds like it'd be extremely hazardous to be working with that kind of concentration.
Patty [1963] reported that 15 to 20 ppm is lethal to small animals within 2 hours [Witheridge and Yaglou 1937]. AIHA [1966] also reported that on the basis of animal data, exposure at 50 ppm for 60 minutes will probably be fatal to humans [King 1963].
So that's something like 240 times the concentration to kill a human in that period of time. Even if one can get the hardware to produce that kind of concentration in a garage, I wouldn't want to do so.
I may be revealing that we dont have many dangerous animals where I love... but is it actually a large number of black widows! I kind of hope the e is something called a window spider an that you misspelled.
I mean even one black widow, and id assume you'd call an exterminator to make sure there weren't any more around the house.
Yes it does. Read the can to see what the spray effects. If it says spiders you are good. But as others have said kill the food source of the spiders and you will have solved the actual problem.