Releasing "House" Spiders Outside

[Ungoliant]

A while back, I read something on Rod Crawford's site that gave me pause:

Myth: Spiders come into houses in the fall to get out of the cold.

Fact: This seemingly simple idea conceals many false assumptions. In reality, house spiders are usually not the same species as the yard or garden spiders outside the house.

House spiders belong to a small number of species specially adapted for indoor conditions (constant climate, poor food supply, very poor water supply). Some house spider species have been living indoors at least since the days of the Roman Empire, and are seldom to be found outside, even in their native countries (usually Europe). Many of these species now live in houses worldwide, and most have been carried by commerce to more than one continent. Few are adapted to North American outdoor environments.

House spiders colonize new houses by egg sacs carried on furniture, building materials and so forth. They usually spend their entire life cycle in, on or under their native building. If a large number appear at a specific season, it is usually late summer (August and September) -- not a notably cold time of year! -- rather than fall, and their appearance coincides with the mating season of the given species. What you are seeing is sexually mature males wandering in search of mates.

The females and young remain hidden for the most part, in crawlspaces, storage areas and other neglected rooms; wall and floor voids; behind furniture and appliances, etc. Generally fewer than 5% of the spiders you see indoors have ever been outdoors.

In contrast, outdoor spider species are not adapted to indoor conditions. Any North American spider that needed artificial shelter for the winter, would have been extinct long before Europeans arrived! Spiders are "cold-blooded" and not attracted to warmth. They don't shiver or get uncomfortable when it's cold, they just become less active and eventually, dormant. Most temperate zone spiders have enough "antifreeze" in their bodies that they won't freeze at any temperature down to -5° C.; some can get colder. The few typical outdoor spiders that do end up indoors, die or at least don't reproduce.

Myth: "I'm very kind to spiders; when I find one in the house, I put it back outside instead of killing it."

Fact: You can't put something "back" outside that was never outside in the first place. Although some house spider species can survive outdoors, most don't do well there, and some (which are native to other climates) will perish rather quickly when removed from the protective indoor habitat. You're not doing them a favor.

In any case, house spiders are mostly harmless and beneficial. Human property rights mean nothing to other species. There was spider habitat for millions of years where your home is now. My advice is, "just wave as they go by."

I often find spiders indoors that don't normally live indoors. (These spiders are almost always males wandering in search of mates.) I put such spiders outside.

But I have to ask: how many spider species are so well-adapted to indoor living that they can no longer survive outdoors in temperate climates?

[Mandy]

But I have to ask: how many spider species are so well-adapted to indoor living that they can no longer survive outdoors in temperate climates?

I think the number of species that can't survive outdoors is really low, actually. And it's probably more like they can't survive, reach maturity, and reproduce... rather than them just dying the same day they're placed outside or whatnot. I think Rod had an interesting point but, yeah, not really all that many species that would die (in my experience, at least). A lot of the synanthropic species can survive outdoors, as long as they can still mosey around the outside of the building and other structures. They might not survive if they were forced to move out into the "real" open, though, because of harsher conditions and a totally different set of species to compete with.

[Ungoliant]

Thanks! I really don't mind the indoor "house" spiders, but I have to put them outside to keep the peace. Fortunately, my husband doesn't mind if they stay on or around the building outside, since they eat bugs.

[alexdesignz]

In my jouse it is take outside or kill. So Outside is better odds. I also do live in CA so my weather is always better outside...

[Mandy]

I always feel odd to admit it since I'm such a spider fanatic, but I put most of the spiders I find outside, too, or I capture them as "pets." The only species I tend to leave be are the Pholcus phalangioides (most are too high on the ceiling to capture, anyways) and the occasional Steatoda grossa that lives under the baseboards in the corners of most of the rooms. I don't let too many others just hang out inside but, then again, the two species I mentioned are basically the two main house-based spiders we ever get here. The rest are occasional wanderers that come in from outside on accident, so those go back outside, or on my spider shelf. :-)

[Reverejack]

I have heard that before, it is completely true.