Killing a Spider
This is a taboo against a specific ACT — killing the spider — layered on top of an already-positive general belief about spiders being present in the house. The bad luck attaches to the killing, not to the spider showing up, which is a different question from whether spiders are welcome at all.
Traceable origin
Earliest known record: English folk rhyme recorded by 19th-century folklorists, e.g. 'If you wish to live and thrive, let the spider run alive'
This is one of the more genuinely traceable minor superstitions on the site: English folklore collections from the 1800s recorded rhyming couplets specifically instructing people not to kill spiders, most famously 'If you wish to live and thrive, let the spider run alive,' with the consequence of killing one often stated directly as rain the following day. The rhyme form itself is a useful marker — rhymed folk instructions were a common mnemonic device for household rules that needed to survive oral transmission across generations.
A recorded rhyme, not a vague folk feeling
Of all the superstitions collected in this category, this is one of the more concretely documented ones, thanks to its rhyming form. English folklorists working in the 19th century recorded the couplet 'If you wish to live and thrive, let the spider run alive' as an established piece of household instruction, with a companion line in some versions specifically warning that killing a spider brings rain the following day. Rhymed household rules like this one were designed to be memorable and to survive being passed down without a written record, and the fact that this particular one still circulates today, largely intact, says something about how effective that transmission method actually was.
The taboo is about the killing, not the presence
It's worth being precise about exactly what's forbidden here. This belief doesn't say a spider showing up in your house is bad — in most versions of this tradition, quite the opposite is true, and a spider's presence is read as neutral or even beneficial, doing useful work catching other insects. What's specifically discouraged is the act of killing one once it's there. That's a meaningfully different shape of superstition than most of the ones in this category, which are usually about avoiding an encounter altogether (walking under a ladder, opening an umbrella indoors) rather than about how you're allowed to respond once the encounter has already happened.
Money spiders: a specific, higher-stakes variant
American and some British folk tradition carries a related but distinct belief around so-called money spiders — typically very small spiders found on a person's clothing or, in some tellings, inside a wallet or purse. Their presence is read as a sign of incoming money, sometimes with the added instruction to let the spider crawl off naturally rather than brushing it away, on the belief that doing so prematurely, let alone killing it, cancels the good fortune before it can arrive. This raises the stakes of the general 'don't kill a house spider' rule considerably: an ordinary house spider risks bringing rain if killed, but a money spider risks costing you the luck it was actively bringing you.
A rare superstition about how you may respond, not just what you should avoid
Most bad-luck rules tell you what not to do in the first place. This one assumes the spider is already there and tells you specifically not to kill it — a genuinely different structure worth noticing.
The plain, practical case for the same behavior
House spiders genuinely do useful pest control, feeding on flies, moths, and other insects that are considerably less welcome guests, and a household that leaves spiders alone will, in practice, tend to have fewer other insects around. It's entirely possible this superstition survived in part because the behavior it recommends — leave the spider alone — happens to be good practical advice regardless of any folklore attached to it, in much the same way several other superstitions in this category ride along on top of genuinely sound underlying reasoning.
Presence and killing are read on two separate pages
What a spider's mere presence in the house means — which shifts more by time of day and context across traditions — is covered on its own page. This one narrows to a single moment: the act of killing a spider that's already there, a sharper, more specific rule than the general question of whether finding one is good or bad news in the first place.
What Different Cultures Say
British and Irish tradition carries the rhymed version most directly, with the rain-the-next-day consequence being the most consistently recorded specific outcome, alongside a broader general sense that a household spider was doing useful, protective work simply by being present and shouldn't be punished for it.
American folk tradition inherited the general 'don't kill a house spider' instinct but attaches it more loosely to general bad luck rather than the specific rain forecast, and adds its own layer around 'money spiders' specifically — small spiders found on clothing or in a wallet, whose presence is read as incoming money, a luck that killing the spider is believed to cancel outright.
Frequently Asked Questions
Does the rain-omen version specify how soon after killing a spider the rain is supposed to arrive?+
Most recorded versions simply say 'the next day' without more specific timing, which fits the loose, mnemonic-rhyme style these household rules were typically passed down in rather than a precise forecast.
Is there a size or type of spider this taboo doesn't apply to, like a genuinely dangerous one?+
The folklore as recorded doesn't generally distinguish by species — it's aimed at the common, harmless house spiders people actually encountered indoors regularly, rather than venomous species that would obviously warrant a different practical response.
Why would a money spider specifically need to crawl away on its own rather than being removed?+
The logic in most tellings is that forcing the spider off interrupts whatever process is bringing the luck, whereas letting it leave in its own time allows that process to complete — a similar 'let it run its course' logic to other patience-based luck beliefs.
Is killing spiders outdoors covered by this same taboo?+
The recorded folklore is specifically framed around the household spider, encountered indoors — outdoor encounters aren't typically covered by the same rule in the sources this belief is drawn from.