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Entomology (Study of Bugs)/Running Spiders in the bathroom



Location: south central PA, about 9 miles North of the Mason-Dixon line, sightings since mid-September.

In the last month we've seen the same type of spider several times weekly in the bathroom.  I identified them with the help of to be Running Spiders.  I'm pretty sure about the ID.  If it means something, they have all been comparable in size.

The first one I was able to catch and release outside, but since then the only thing I've been able to do is kill them.  (If it's a choice of lose it or kill it, there's no real choice for me.)

I would rather catch them in a "bug jar" (I have them in strategic locations in the house) to let go.  However I've been reading up and found out that this is the time of year that Running Spiders come in from outside AND that they are considered a Sac spider.

When we first moved here 20 years ago we had an infestation of Yellow Sac Spiders, mostly upstairs.  My little girl was continually getting bitten and though there wasn't necrosis, there was significant swelling and pain/itching, plus the bite took weeks to go away.  

The Yellow Sac Spiders always seemed to be coming down from inside the drop ceilings in the bathroom and hallway upstairs.  At least that's where they'd run to when I missed getting one with a flyswatter.  We had cats, a corn snake (who is 20yo this fall), an African pygmy hedgehog and a leopard gecko, so couldn't use spray pesticides.  On the advice of a pest control company we got several of the Hot Shot No-Pest Strips and placed them up inside the drop ceilings.  We felt they were the safest option.  We replaced the old No-Pest Strips with new ones 3x a year for a couple of years, and now rarely see a Yellow Sac Spider though we haven't replaced the strips for YEARS.

Though I find spiders interesting I admit I'm scared of them.  I'm more into snakes and other reptiles.  My question is, are Running Spiders known to bite without provocation, like Yellow Sac Spiders?  And if they do bite (I know all spiders have venom and can bite) is their venom dangerous in any way?

I have no compunction about killing any Yellow Sac Spiders  in the house (I'm holding a life-long grudge!) but would rather "re-home" any other kind.  In the same month that the Running Spiders appeared I captured 2 jumping spiders in my kitchen and took them outside to the picnic table.

We've never had Running Spiders before, and having so many makes me wonder if they are now an infestation, taking the place of the Yellow Sac Spiders.  :(  They're kind of pretty, all red like that, but the Sac spider thing has really freaked me out due to our history.

Any suggestions, reassurances, whatever would be greatly appreciated.  Thanks so much!


Hi, Linda:

First I have to make sure we are talking about the right spider.  Do you mean Trachelas tranquillus ?  Here is a link with an image:

If so, then having them come indoors is not unusual, especially at this time of year.  I do think they are looking for a place to overwinter....

No, they are no longer considered dangerously venomous in any way.

Lastly, I'm concerned that you have an "exclusion problem," meaning that your home offers few barriers to *anything* trying to get inside.  I'd recommend repairing worn weatherstripping around doors; mending holes in windowscreens; sealing any other openings to the outdoors, such as where plumbing and electrical conduits enter or exit.  Steel wool packed into those openings offers more resistance to rodents, too.  Be careful when you bring anything in from outdoors, especially firewood, potted plants, shoes and apparel left outdoors overnight, etc.  Many insects and spiders ride in on such objects.

Autumn is mating season for many spiders, too, so male spiders of nearly all species, even those normally confined to webs, are wandering in search of females.  They may stray indoors at that time.  Spiders that hunt without webs will of course occasionally find their way in no matter how secure the home is.

Hope this helps.  Please feel free to ask specific follow-up questions.  Any lady who is a friend of reptiles can't be all bad, so no worries for killing the odd interloper when there are plenty more from whence it came :-)  Love that you have such an "old" corn snake!  Also like how literate and eloquent you are.  You should see some of the other questions I get.  Take care.


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Eric R. Eaton


I answer insect and spider identification questions ONLY. Attach images if possible. No "what bit me?", "what do I feed this bug in captivity?", or science fair project questions please. NO TECHNICAL QUESTIONS ABOUT INSECT PHYSIOLOGY.


Principal author, Kaufman Field Guide to Insects of North America. Professional entomologist employed previously at University of Massachusetts, Chase Studio, Inc., and Cincinnati Zoo; contract work for West Virginia Department of Natural Resources, Smithsonian Institution, and Portland (Oregon) State University.

Author, Kaufman Field Guide to Insects of North America, Missouri Conservationist magazine, Ranger Rick, Birds & Blooms, Timeline (journal of the Ohio Historical Society). I have contributed to several books as well.

Oregon State University, undergraduate major in entomology, did not receive degree.

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One of the top 50 experts in all categories for, 2009.

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Principal author of the Kaufman Field Guide to Insects of North America, Smithsonian Institution (contract), Cincinnati Zoo (employer), Portland State University (contract), Chase Studio, Inc (employer), Arkansas Museum of Discovery (guest speaker). Currently seeking speaking engagements, leadership roles at nature festivals, workshops, and ecotours.

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