How to kill spiders?

No, I don’t mean like “With a shoe.” :slight_smile:

Every year around this time we get a fair number of spiders wandering around our home (mostly the finished basement). Some of 'em are freaking huge (I killed one last night that must have been at least an inch-and-a-half long, and not all legs like a daddy long legs).

Anyway, last year I asked our exterminator to spray for spiders. He said they don’t have anything that kills spiders, they just spray for other bugs and when they die, the spiders die for lack of food. It took quite a while and, frankly, I didn’t see any marked decrease in the number of spiders. I figure enough new bugs might come in to keep 'em well enough fed to at least survive.

The whole thing sounded a bit strange to me. No poison to kill spiders? C’mon, there must be! The only thing I could think of was that anything poisonous enough to kills spiders would be harmful to us as well.

Anybody know the straight dope on this?


Many insecticides are designed to be effective when ingested. Carbaryl (Sevin®) is applied to insect foods and they die when they eat the foods. They will also die when you hit them with it directly, entering their breathing spiracles, but they generally don’t die by walking across it. Rather, colony insects track it back to the nest and walk across their food supply, poisoning it. (This makes it hard to use on spiders: You have to dust live bugs with it to get them to ingest it, the bugs die, the spiders won’t eat them. Few spiders have colonies, so they don’t tend to track floor-sprayed poisons back to their food supply.)

Diazanon®, however, is topical as far as I know. Pyrethrins are also topical and are a fairly common household application.

I have no idea why the pest killer claimed that they wouldn’t work on spiders. Maybe they concentrate on using Sevin®, which is a prettry safe product. Maybe spraying baseboards is ineffective for spiders who tend to not follow walls the way ants do.

(Of course, the bigger question is “Why are you trying to kill the poor spiders?” The one you described killing was probably a wolf spider just keeping your basement free of vermin. I spend a fair portion of my summers rescuing them from the utility sink in the basement so that they don’t drown when we do laundry.)

The spiders are your friends. They are symptoms of your real problem. If you have lots of spiders in your basement that means you have lots and lots of bugs as well.

Get a bunch of those fogging bug bombs, seal your basement and set them off. Ideally that will kill everything in your basement.

Next you get to clean up. Be sure and clean all the surfaces thoroughly before you resume habitation of your basement.

You probably also want to find where the bugs are coming in. Window wells, mortar cracks, and conduit (usually a bad install of cable or sattelite tv,) are likely candidates.

Tom’nDeb is right (as usual) you might want to reconsider killing the little octoappendigial sentinels. Think basic biology - the number of spiders living in your basement is limited by the amount of food at their disposal. Assuming they don’t eat dirty socks, the number of other insects / pests is proportional to the number of spiders. Getting rid of the spiders is tantamount to walking around without your skin. OK, so it would not be nearly as gross or painful, but you get my point - you first line of defense is gone.

You could douse your basement with poisons. Great. Not so good for the environment to dump chemicals onto your property. If not for the speckle-backed weasel owl, than for you and your family. Where do you think those chemicals are going to run off to? If you spray inside, there is little chance of rainwater taking them away. No, they’ll sit and sit and degrade into whatever other nastiness comes down the line, or they will get kicked up into the air from time to time waiting to screw around with your endocrine system.

So now you’ve sprayed and made a sterile wasteland of your basement and surrounding property. Fine, no one wants bugs, no matter how helpful, crawling on their faces at night. What happens next year? Who is going to be the first to colonize the wide expanses of your basement? Nature abhors a vacuumed carpet, and will do what it can to fill any niche that is available. If you don’t have a toxic dump in your basement, it will be nice and palatable for a new family of insects. They, not the spiders, will be the first to move in. There will be some lag time before the predator / prey ratio reaches some sort of dynamic equilibrium. You are now back to square one. If you dump toxins every couple of years to keep yourself Beatle, and spider free, your… well, your testicles will shrink. I’ll find a cite for that somewhere.

Find a way to limit the immigration of the Coleopterites into your house, and the spider population will fall on its own. I feel for you. I’d rather stare down ten beetles than one big, ugly, hairy, spider. But remember, that spider is like a big, ugly, brutish Marine. He might make you nervous, but be glad he’s out there.

That is all for now. I have to leave to go hug a tree and smooch a spider.

Household pesticides are designed to break down pretty quickly into harmless components. I say fog at will, and better living through chemistry.

I got the following from a web page at University of Nebraska-Lincoln. It’s intended as a rememdy for daddy longlegs, but I don’t see why it wouldn’t be more broadly applicable:

The extension officer noted that home spider invasions are worse in moist years, which this certainly seems to have been so far (at least in the northern US). Also, he did not recommend spraying anything indoors (as Rhythmdvl noted, not a good idea for other reasons).

I appreciate what spiders do; heck, I used to leave a small population of them set up by my front door, specifically to nab any ants that made their way in (the door was old and didn’t fit the frame tightly), and they did a fine job. Still, I’m sympathetic to not wanting to see huge freaking spiders all over the basement… if you get rid of the other bugs, as Scylla suggested, and keep new ones from coming in, hopefully your spider problem will vanish as well. Good luck.

The recommendation against spraying indoors applied to the heavy-duty pesticides mentioned on the web page, not to fog bombs.

Still, if you have pets, you might want to find out first how sensitive they might be to the pesticide and/or residues before using fog bombs indoors, and make plans accordingly.


I can tell you that Yard Guard will kill tarantulas and scorpians, and I’ll bet it works on your spiders. The only problem is that it needs to be spayed directly on the critters.

I worked my way through college for a couple of summers working for a pest control company – kind of an unusual career choice, since I’m something of an arachnophobe.

Spiders are very susceptible to respiratory poisons, such as pyrethrins. (Warning: what follows will be incredibly over-simplified.) Their lung system is something like an accordian, and it very quickly circulates the poison throughout the little critters and they usually die very quickly.

You can get some really mild stuff and it should do the trick without causing horrific harm to the environment. Something with mild residual aspects to it should keep them away for at least the season.

Spiders are good at keeping down flying insect populations. Even a spider-hater such as myself doesn’t just go around killing the hideous beasts indiscriminately. Only those that make the foolish life choice of scurrying into my house.

Either Tomndebb is pulling your leg, or he’s never seen a wolf spider.

Years ago, I had the misfortune to wake up and find one of the critters in bed with me - it was at least 4-5 inches in diameter. I didn’t stay too long to really examine it; in fact, I managed to get from the bedroom to the living room without touching the floor. (BF at the time captured it and put it outside.)

DavidB, if you have a lot of little spideys due to a recent hatch, a vacuum cleaner with a hose attachment can be a big help - just don’t forget to throw out the bag.

Some wolf spiders can be quite small; the ones I see in my house are typically three quarters of an inch to an inch and a half across. Pages like this one suggest that that is typical, and the spider you saw was probably a tarantula.

Dad always used to say “get some hedge apples.” So every fall we would pick a grocery sack full of Hedge apples and put them all over the basement. Well I didn’t see any spiders that winter but come to think of it you don’t usually see them in the winter.I guess it worked at home but that was a new house. and in town.Here in the country we always have them Eventhough I tell the kids “Go get some Hedge Apples”
I believe I’ll try to burn one of those Pyrethrin candles in the basement.It is probably the safest of all the Spider killers I ve heard of,except for the shoe.

A word of caution

Before you use any chemical remove or cover any fish or birds.
Wouldn’t want to be responsible for killing tweedy bird or charlie fish.

Ummm…I’m not sure where those little bitty spiders came from, but in the Northwest, wolf spiders can get as big as your hand. They will leap too, and move extremely fast. Gives me the willies just thinking about them. Yuck.

Tarantulas on the other hand, come in all sizes too. I have seen them as small as large wolf spiders, and as large as dinner plates.

A short story:
One night I woke up at around 2am, slowly realizing as I came out of the sleep fog that for some reason, I has something in my hand. This was naturally in the dark, but I could feel a furry ‘something’ the size of a large hamster struggling in my grip. Ok, I told myself, lets see what is in my hand. It hasn’t bit me yet, so I can at least identify it before throwing it across the room shrieking…so I turned on the light, and there in my hand was…

my pet hamster. And I bet you thought it was going to be a gigantic spider, didn’t you?

Hairspray has kind of a cool affect on them!

One question I have is is the exterminator a friend that you talked to or someone you have comming in anyway?
I asked ours about it once and he said about the same thing. Basically that spiders are on site kill.
But with what everyone else is saying that if you insects grow less than so will the spiders because of lack of food. That makes sense to me, but we still have spiders lurking around and watching and waiting till just the right time to jump out at 3am when it is dark and you are half asleep and you feel them as you reach out for the light switch!
Sorry guys I was having a flash back to last summer!

Thanks for the suggestions, folks. I’m not going to go with a bug bombing because I have two small children and the basement is where almost all their toys are. This also rules out some of the nastier chemicals. But I will be asking the exterminator about this again, armed with some of the info here.

Also, Kricket (who probably doesn’t want to be bug-bombed) said:

Someone I had coming in anyway.

Well, why don’t you just use a broom? Once you get the spider, put it outside. Some of those big spiders do bite but its like a bee bite.

My mother has a daylight basement and a chronic problem with bugs crawling in through the patio doors. Until she discovered a product called Ortho Home Defense, which she now swears by. It comes in a big jug, premixed, with a sprayer. You spray it in small amounts all around the baseboards and especially inside and outside the patio doorsills, it doesn’t smell too bad, it lasts 4 months, and she says it WORKS.

If you have small children, you can just spray it behind the bookcase or something, where they aren’t likely to touch it. It’s a chemical called Bifenthrin. They use in on golf courses and athletic fields for control of mole crickets and armyworms, so it can’t be too toxic to walk on.

And yeah, I know it’s rated as a “possible carcinogen”, but then, so are peanuts and saccharin.

The more I think about it, DavidB, I’m wondering how any pest control guy who knows what he’s talking about could tell you that you can’t kill the spiders; you can only kill the insects that they feed on.

That is SO wrong. Spiders are EASIER to kill than most insects.