r/explainlikeimfive • u/Electronic-Volume-56 • 1d ago

Biology ELI5 Why are Giant house spiders so big?

I am complete and utter arachnophobe and in my country we are heading into the time of year know as spider season when all those massive house spiders get horny and run around looking for a mate and scaring me senseless. After getting my neighbour to save me from a particularly huge giant house spider I started thinking- why are they so big? They have been living in our houses for so many generations now, surely evolution should have selected smaller spiders that can better hide in our homes and avoid getting caught/squished/eaten by pets, rather than these hairy behemoths!

154 Upvotes

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374

u/I_might_be_weasel 1d ago

The answer is more disturbing than you realize.

Because there are enough bugs in your house to feed them.

130

u/NickDanger3di 1d ago

Were. There were enough bugs to feed them. By the time you see them, they are running out of food, and getting very, very hungry.

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u/dddd0 1d ago

No, the males do not get hungry. When they're adult they mostly stop eating and focus entirely on finding females, that's what they're wandering for.

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u/VoilaVoilaWashington 1d ago

Nah, usually it's horny, not hungry. You underestimate the amount of bugs in crevices of your home.

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u/Lathael 1d ago

My favorite are house centipedes. I almost never see them but when I do, I know they found a crack to slip through. They typically hang out in the walls.

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u/Pavotine 1d ago

I made peace with my house centipede or more likely centipedes. We ignore each other and they hunt just about every other insect in the house. They also seem to have learned my routine and they now scarper when I turn on a light at night so I hardly see them much.

•

u/Lathael 8h ago

It's a very easy truce. They kill things I don't like, they don't show their face 99% of the time to me so I don't have to think about it. Win/win.

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u/IAmJacksSphincter 6h ago

You all are making me so thankful I live in the North where I haven’t even heard of house centipedes till this thread.

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u/Lathael 6h ago

Don't worry, house centipedes live in the entire continental united states, as well as into Canada. They're probably in your house, watching you sleep, killing all the things that want to prey on you while you sleep.

There's also more types of house centipedes. There's the 'house centipede,' which I've never personally seen, and other types like stone centipedes and so on and so forth, and I have likely seen one of those variants, that also live in houses (and I referred to as house centipedes in error as well).

There is an extremely good chance that unless you live in a place like Alaska, you have centipedes living somewhere in your house. The exception being if you have a more modern house with injection ports for pesticides that can distribute the chemical to common entry points, where it's less likely but still probable they're in the house.

Don't worry, these creepy little blighters are the reason there's fewer creepy blighters bothering you. They also hate the light and don't want you to see them either. So if you ever see one, just shine a light at it, have your panic attack, and then remember that they're there to feed on the things you're also afraid of.

By the way, as full disclosure, I also find them creepy.

30

u/Electronic-Volume-56 1d ago

This the time of year the males turn into sprinters racing around to mate with female...with their boxing glove sex organs...

•

u/Dnaldon 16h ago

That's not really disturbing. The disturbing part is the big spiders.

11

u/Electronic-Volume-56 1d ago

That is indeed a disturbing fact

9

u/Honkey85 1d ago

That's the main reason, I love spiders. They eat bugs.

•

u/I_might_be_weasel 23h ago

Spiders are a symptom, not a problem.

6

u/The_Frostweaver 1d ago

Do they not have screens on their windows in Australia? Keeping creepy crawlers out seems like it should be more of a priority.

Ants, flies, mosquitoes, spiders, snakes, nope nope nope!

The house exists to separate me from nature, it is my castle and it should be fortified against any and all intruders!

42

u/[deleted] 1d ago

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17

u/Ellkoy 1d ago

Hell.

7

u/VirtualLife76 1d ago

Texas isn't a country.

4

u/zed857 1d ago

Can't be Texas, OP spells neighbor with a U.

1

u/buzzhaircut123 1d ago

That implies OP is from UK(unlikely) or a former british colony..large spiders probably means Australia. Its spring down here and bugs are moving.

1

u/mfigroid 1d ago

Tell that to a Texan's face and see how that goes for you.

1

u/VirtualLife76 1d ago

Having lived in that cesspool for years along with having a big mouth, it can be entertaining.

14

u/nankainamizuhana 1d ago

Here’s the map of their locations for you to avoid.

5

u/lalala253 1d ago

Why do they also live in iceland

Why do they live in the middle of an ocean

9

u/geeoharee 1d ago

Those are islands dear
edit: except that one in the North Sea which I think is just someone fucking up his location pin

3

u/Pika256 1d ago

So that's what they are!! I've been trying to take pictures of them to get an ID, but they move fast and I'm chicken shit.

3

u/Zuzublue 1d ago

Oh thank God. The nearest one is over 300 miles from me.

9

u/Potatoez 1d ago

They're originally from Central Europe and UK but have been introduced to the Pacific Northwest in America.

5

u/Monotreme_monorail 1d ago

I’m on the west coast of Canada and yeugh I hate spider season.

Luckily I have three cats so these days I just see their crumpled corpses after a cat has pounced them flat!

3

u/pktechboi 1d ago

I'm going to guess Scotland, we do get extremely big ones this time of year. good news is they're not venemous, at least.

1

u/Snapitupson 1d ago

If it's the spider I think it is I'm fairly sure they can bite and has a little venom.

3

u/phoenix64mbr 1d ago

Do you come from a land down under? 🎶🎶🎶

5

u/stanitor 1d ago

When Australians post on reddit

9

u/AFineDayForScience 1d ago

"That's not a spider. This is s spider."

3

u/kevlarbaboon 1d ago

I see you've played Spidery-Spoony before

2

u/stanitor 1d ago

That's a spoon.

4

u/no_va_det_mye 1d ago

Thats funny because australia has waaay bigger spiders than the giant house spider.

2

u/r0botdevil 1d ago

I've seen quite a few of them in Oregon, USA.

1

u/Obtusus 1d ago

Time to plan your move to either McMurdo or to Amundsen-Scott.

1

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69

u/February30th 1d ago

On the ‘surely evolution should have selected smaller spiders that can better hide in our homes and avoid getting caught/squished/eaten by pets’ point

- there are a lot more evolutionary pressures out there than Prince Fluffykins running around your house

- evolution typically works over much longer timescales

- small doesn’t always means best for a spider. For example small means they are less able to defend themselves from predatory insects

- your house might not be their only domain and habitat

- house spiders aren't necessarily getting caught and squished often enough for this to present strong evolutionary pressure

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u/Electronic-Volume-56 1d ago

This makes quite a bit of sense

7

u/Hobbit1996 1d ago

house spiders aren't reproducing in your house often, they mostly come from outside so the "evolution" isn't happening anywhere close to your house

129

u/[deleted] 1d ago

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23

u/imaginary0pal 1d ago

Moderately sized house spiders don’t have the same ring to it

13

u/OGREtheTroll 1d ago

Spiders Of Unusual Size

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u/A_Flamboyant_Warlock 1d ago

Sounds S.U.S.

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u/imtougherthanyou 1d ago

Came here to write this

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u/Buttspirgh 1d ago

Adequate House Spiders

3

u/wbruce098 1d ago

Amicably Sized House Spiders?

4

u/Temporary_Pie2733 1d ago

Insufficiently Small House Spiders.

5

u/kingvolcano_reborn 1d ago

Grower, not a shower house spider

2

u/tothecatmobile 1d ago

Its when the miniature house spiders are massive. Thats when you worry.

1

u/Hypamania 1d ago

Yeah, frig, the name's on the tin

1

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15

u/[deleted] 1d ago

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u/VoilaVoilaWashington 1d ago

Seriously this. I like spiders. I let them live in my house, generally. They're a good thing.

A few days ago, I was reading in bed when one of them ran across my white sheets. I screamed a scream not heard since the dawn of man, and I think my heart rate was well outside healthy ranges.... but once I realized it was just a lil' house spood, I was fine.

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u/Rich-Juice2517 1d ago

Running ACROSS the sheets with me in them? Nope. I turn into Al Capone from the untouchables

If they stay in a corner from me and just kinda stay away? We're fine. It's when they start coming towards me that we're not fine

1

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13

u/[deleted] 1d ago

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1

u/Reckfulness 1d ago

Oh hell no, thats what doors are for

1

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1

u/weaver_of_cloth 1d ago

Those things are as big as my hand!

2

u/OGREtheTroll 1d ago

It's all legs though. When you kill them and they curl up they are kinda small.

1

u/blofly 1d ago

I love my spider bros. I will relocate bigger ones if needed, but I dont mind the occasional visit from juvies. They really keep the flies and other bugs.out, and we have established a pact.

So far, they have kept their part of the bargain.

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u/GIRose 1d ago

There might be evolutionary pressure for them to get smaller to be better out of sight.

There is ALSO evolutionary pressure for them to be bigger than all of the other rival males that are around.

The size they are now is the equilibrium point where they are currently sitting. Give it a few thousand years and they might be some different size if one of those factors gets more important.

43

u/pktechboi 1d ago

they're often actually garden spiders coming in to seek shelter from the cold. if it helps at all, most spiders are both cannibalistic and extremely territorial, so if you can tolerate even one it is likely to keep others away.

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u/geeoharee 1d ago

We're talking about a specific spider, Tegenaria gigantea as it was (it's Eratigena now but I liked the old one better). It's a commensal, they used to live under rocks and now they live behind furniture.

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u/pktechboi 1d ago

I'm too arachnophobic to search that, but noted!

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u/geeoharee 1d ago

Understood! If it helps, the phenomenon of 'seeing these big lads running around and posting about it on Reddit' is an autumn thing - has to do with their lifecycle - and will die down as the weather gets colder.

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u/VeneMage 1d ago

Wait, they can post on Reddit now? Evolution is getting out of hand.

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u/Rainuwastaken 13h ago

On the internet, nobody knows you're a dog.

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u/Nox_Dei 23h ago

Understood, packing my stuff and moving to Antarctica.

1

u/Flamekorn 1d ago

Yeah usually September-October is the season I find this buggers and have to put them in the garden. After that its kind of like they got into their places

11

u/VoilaVoilaWashington 1d ago

...oh. I was thinking they would be GIANT. I don't think I've seen 'em here, but growing up on the west coast of Canada, they were super common.

3" across is big, but not, like... BIG!

16

u/geeoharee 1d ago

OP spelled neighbour with a U and posted in the UK evening, so if they are UK as I am, we are not used to Big Wildlife

7

u/SillyMattFace 1d ago

The more I’ve travelled, the more grateful I am for the UK’s relatively small and harmless creatures.

Don’t have to worry about some poisonous spider or snake under every rock and log. Don’t have to worry about anything hunting the family pets.

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u/ijuinkun 1d ago

Ah, I was thinking Australian myself.

1

u/funny-hats-only 1d ago

I have house centipedes. Freaky little buggers but I consider them allies in my fight against the other pests.

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u/pktechboi 20h ago

oh, house centipedes! have you read the book Absolution by Jeff VanderMeer?

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u/funny-hats-only 18h ago

I have not! Will it make me more or less scared of bugs?

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u/pktechboi 17h ago

there is a bit with house centipedes that is uh. intense. also it jumpscared me worse than any book I have ever read. (very light spoilers I guess??? just in case.) on the VERY last page, after the acknowledgements and everything, there is a larger than life silhouette of one and I did not see it coming, turned the page and dropped the book because I thought it was a huge spider 😂

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u/bdog143 1d ago

Despite the name 'House spider', their ideal habitat is outside, not in houses. Modern houses are too dry and clean for them to survive for long, a few just end up inside by accident. Being big means they can eat bigger prey, lay more eggs etc.

4

u/greatestbird 1d ago

That’s entirely wrong, they’ve evolved to live in caves and human homes are ideal caves. Putting them outside will pretty much condemn them to death

3

u/Pavotine 1d ago

I banish big house spiders to the shed or garage. They seem to do alright there.

3

u/bdog143 1d ago

Caves are outside. They tend to be cool, damp and full of tiny terrors that make ideal spider food. That would have been true of European houses back when the giant house spider got it's name, not so true now. Most of my house is 130 years old, and any spiders that elude the cat tend to go tits up within about a week because it's warm and dry. The giant house spiders in my shed and garden do not - they're about 50% larger than any that I've found in the house.

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u/jamcdonald120 1d ago

houses are a new thing. only some 10 thousand years old. good houses even younger. maybe 150-300 years?

evolution operates on the 100 thousands to millions of years. it hasnt even noticed houses. "house" spiders evolved for completely different environments like forest with ground cover or caves, they found your house and said "well this is a nice cave" and moved in. its warm and dry, and lots have other bugs also want to be warm and dry.

also, spiders tend to look a lot bigger than they actually are. those leggs are very long and flexible. the main body is the part that has to fit through things and is much smaller

3

u/threemo 1d ago

Well - yes and no. Evolution doesn’t really have anything to do with years, but iterations and life cycles. Spiders are cycling far more quickly than us and thus capable of evolving more quickly.

That said, I doubt whether houses exist or not is forcing much in the way of evolution. Spiders of any size are doing just fine, so evolution isn’t eliminating either.

5

u/DiscordantDiscordian 1d ago

Not necessarily, evolution can be pretty speedy if the pressure is high enough. 

The best example are how african elephants are losing their tusks due to intense poaching over the last 200 years. 

And since we started building houses we turned the wolf into both great danes and pugs.

While a lot of indoor species started out as cave dwellers most have adapted to the special circumstances, with higher metabolisms and day-night cycles among other things

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u/rastagizmo 1d ago

Think about the size of your toes.

Now think about how big a spiders mouth must be in proportion to their bodies to allow them to suck on your toes when you are sleeping.

That's why they are so big.

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1

u/Electronic-Volume-56 1d ago

I completely understand they cant hurt me...its such an irrational fear, but seeing them just triggers such a panic in me

1

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1

u/daaangerz0ne 1d ago

Have you met the cockroach eating ones?

•

u/crappy_ninja 16h ago

Maybe it's because they are finding a lot of other bugs to eat. All those little ones that are better at hiding from you.

1

u/RandomErrer 1d ago

A big spider is a well fed spider. Your 8-legged buddy is feasting on bugs, so let it be.

1

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1

u/Electronic-Volume-56 1d ago

This is my nightmare

1

u/dddd0 1d ago

Probably a lot of roaches and other vermin in your house.

1

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1

u/rasputin6543 1d ago

If they weren't that big, then they wouldn't be giant house spiders.

-1

u/Bar_ki 1d ago

Because the spiders are as big are as big as the doors.

-1

u/UnwrittenRites 1d ago

They really aren't that big. Spiders are generally pretty small but there are some that are comparatively large (for spiders) so I wouldn't consider 4 inches to be "so big" even for spiders. Ranking Each Of The 7 Continents By Their Largest Spider (sadly despite the video title it isn't really focused on size but this video shows some cool spiders)