The spiders are there because there are insects, a food source, there, so which insects are down there, how are they getting in, why are they in the basement?
Eliminate the insects and the spiders will leave due to lack of a food source, and then you need spray something that will kill off these wee buggers and that will also damage your health.

Purchase some Miracle II soap. It's a concentrate. Mix 1.5 tsp in a quart spray bottle filled with water. Be sure to fill the bottle with the water first as the soaps foams a lot. If you put the soap in first you it will suds up too much to get the water in the bottle!

Miracle II is an incredible product. It is all natural. I use it as soap. It doesn't kill the insects by poisoning them but rather by drowning them. (Something about the viscosity smothers them. Not a pleasant thought but at least this isn't poison!)

It's also a wonderful repellant. Ever since I started using MII for cleaning and as a soap I rarely see an insect in my entire house.

You can't use it on wood. It will also make linoleum slippery so I don't use it on the floor.

It also kills and repels those orange bugs that eat Oriental Lilies and aphids and any other insect except perhaps japanese beetles.

This is a link to their home site but many people sell it on the web and on ebay.

Don't let the religious component put you off. This stuff is incredible. We go through gallons of it in June for the insects in the yard. It has a cumulative effect. We spray a couple of times a day for a week or so and the bugs just don't come back!

Good luck!

Celtic Rose

Here is a link that might be useful: Miracle II Soap

What the HECK are 'Nervology' and 'Spiritual Chemistry'??? ;-) Yikes.

I'm not sure....it's been years since I've been on Miracle II home site, but as I said - don't let anything they say put you off. This stuff is absolutely The Best Thing since sliced bread.

I haven't told my husband about the "spiritual" component in the spray. He's a crusty old Irishman and would scoff at any such mention. But every spring he's always yelling, "Get the spray!!!!!!!" "Spray your roses!" "Spray those lilies!" He swears by the stuff, too.

I killed a swarm of termites with it a few years ago. I stood and waited until they died to make sure it worked. It did. Without poison. Then I went inside and took a shower with the same soap!!! (Higher concentration for the soap, of course.)