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This is a factoid I heard as a kid at some point, probably on a playground somewhere, and just accepted without question in the way that children do:

All spiders are venomous, but most of them aren't venomous enough to harm humans.

(I'm pretty sure the wording used was actually "poisonous", because the distinction between venom and poison is a little too technical for a nine-year-old, but I understood it at the time to mean what I now know is called "venomous".)

Is this true? Are all spiders venomous? Or is this just one of those made-up "facts" that circulates playgrounds and campsites?

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    $\begingroup$ @anongoodnurse I have never heard of herbivorous spiders. Are there some? That also doesn't mean they don't have venom for self-defense or just vestigially, either. $\endgroup$
    – Hearth
    Dec 15, 2023 at 19:44
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    $\begingroup$ @anongoodnurse I did look it up, but the state of search engines right now means it's hard to find anything, especially anything debunking common misconceptions and playground rumors (you're more likely to get some LLM arguing that they're true). $\endgroup$
    – Hearth
    Dec 15, 2023 at 19:55
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    $\begingroup$ @anongoodnurse Bear in mind that I'm an electrical engineer, not a biologist or zoologist or anything, and I almost certainly don't know the right terms to make a search engine give me actual scientific articles and not "10 cool facts about spiders you won't believe" repeated a million times. Yes, I'm exaggerating, but it's hard to find information that's actually reliable these days. $\endgroup$
    – Hearth
    Dec 15, 2023 at 20:02
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    $\begingroup$ @NilayGhosh Beware of the information in your link, it states they are non-venomous, but that is incorrect in absolutely every case listed there. They may have venom insignificant to most humans, but that's a different thing. $\endgroup$ Dec 16, 2023 at 7:52
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    $\begingroup$ @PierrePaquette Is it true that many spiders' fangs are too short to pierce human skin? That's another thing I heard on playground rumors (usually in the form of "(whatever spider species they just saw) is the most poisonous spider but it's harmless to humans because its fangs are too short"; I expect the "most poisonous spider" part is wrong, but I'd never realized the "fangs are too short" part was actually true. (The spider in question in that rumor was usually the daddy longlegs in my experience, which I know isn't even a spider.) $\endgroup$
    – Hearth
    Dec 16, 2023 at 17:55

1 Answer 1

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I searched Google for "non-venomous spiders".

The first result that came up was Uloboridae (Wikipedia):

Uloboridae is a family of non-venomous spiders, known as cribellate orb weavers or hackled orb weavers. Their lack of venom glands is a secondarily evolved trait. Instead, they wrap their prey thoroughly in silk, cover it in regurgitated digestive enzymes, and then ingest the liquified body.

However, non-venomous spiders are atypical, and it is true that most spiders that humans don't consider harmful are still venomous to their prey; the playground statement is a reasonable approximation.

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    $\begingroup$ I don't know why this got a downvote; it definitely answers the question. Have an upvote. It didn't occur to me to use that specific search term; I just tried "all spiders poisonous", "is it true that all spiders are poisonous", and so on--which didn't turn up any useful results. $\endgroup$
    – Hearth
    Dec 16, 2023 at 2:11
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    $\begingroup$ @Hearth Which makes sense, because being poisonous is not the same as being venomous. Venom is injected, poison is ingested or touched, so for example Pitohui dichrous is poisonous but not venomous, while Acharia stimulea is venomous but not poisonous, despite physical contact being the hazard for in both cases. $\endgroup$ Dec 16, 2023 at 13:43
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    $\begingroup$ @AustinHemmelgarn I didn't really realize that "venomous" would be the correct term until I was typing up the question here, yeah. It's not a distinction that comes up often when working as an engineer! $\endgroup$
    – Hearth
    Dec 16, 2023 at 13:45
  • $\begingroup$ You know, after this description I have decided that I actually prefer the venomous spiders ;-). $\endgroup$ Dec 19, 2023 at 1:26
  • $\begingroup$ Considering that all spiders inject digestive acids into a prey, the method and speed of the venom is debatable. Here's an interesting spitting spider: youtube.com/watch?v=vUUm2OCMCzY they catch their prey by spitting a fluid that congeals on contact into a venomous and sticky mass. The fluid contains both venom and spider silk in liquid form, though it is produced in venom glands in the chelicerae. The venom-laced silk both immobilizes and envenoms prey such as silverfish. en.wikipedia.org/wiki/Spitting_spider found in America. $\endgroup$ Dec 21, 2023 at 7:37

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