You're cleaning behind the couch or maybe moving a box in the garage when you see it. A small, dark shape scurrying across the floor. Your brain immediately tags it as a spider, but then you pause. You count. One, two... six? Wait. Spiders are supposed to have eight legs. That’s the rule. So, can a spider have 6 legs, or have you just discovered a weird new species of insect that looks exactly like a house spider?
The short answer is yes. Absolutely. But it’s not because they were born that way.
Biologically speaking, every single spider on the planet belongs to the class Arachnida. By definition, arachnids possess eight legs. If an animal is genetically programmed to have six legs, it’s an insect. It’s a hard line in the sand of taxonomy. However, the real world is messy. Nature is brutal. Spiders lose limbs like we lose umbrellas—frequently and sometimes without much of a fuss. If you see a six-legged creature that looks like a spider, it’s almost certainly a spider that’s had a very rough week.
The mystery of the missing limbs
Spiders live dangerous lives. Between escaping birds, fighting off rival spiders, and dodging the literal "bottom of a shoe," they are constantly in harm's way.
Most people don't realize that spiders have a built-in survival mechanism called autotomy. This is the voluntary shedding of a limb. It’s a lot like how a lizard can drop its tail when a predator grabs it. If a bird grabs a spider by the leg, the spider can actually "switch off" the connection at a specific joint. The leg pops off, the spider runs away, and the bird is left holding a tiny, twitching snack. It’s a high price to pay, but it beats being eaten.
You’ll also find that spiders lose legs during a bad molt. Molting is incredibly stressful. To grow, a spider has to crawl out of its old skin (the exoskeleton). Sometimes, a leg gets stuck. If they can't wiggle it free, they’ll simply abandon the leg to save the rest of their body.
How to tell if it's a spider or an insect
So, if you’re looking at a six-legged critter, how do you know for sure what it is? Look at the body segments. Insects have three: a head, a thorax, and an abdomen. Spiders only have two: the cephalothorax (a fused head and thorax) and the abdomen.
Also, look at the face.
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Spiders have pedipalps. These look like two tiny, extra legs right next to the mouth. In some species, like jumping spiders, these are very prominent. If you see six walking legs and two little "arms" up front, you’re looking at a spider that’s lost two of its main legs.
Can a spider grow its legs back?
This is where things get really cool. If a spider is still young and has a few molts left in its life cycle, it can actually regenerate its legs.
It doesn't happen instantly.
The first time the spider molts after losing a leg, a small, thin, pale version of the limb will appear. It might look a bit stunted or "weak" compared to the others. After another molt or two, that leg will often be indistinguishable from the original ones. Scientists like Dr. Eileen Hebets, who studies arachnid behavior, have observed that while a missing leg might slightly change how a spider moves or hunts, they are incredibly adaptable.
However, if an adult spider—one that has reached its final molt—loses a leg, it’s stuck that way. For a fully grown female tarantula or a mature male house spider, can a spider have 6 legs for the rest of its life? Yes. And they usually manage just fine.
Why 6 legs aren't a dealbreaker for survival
You might think losing 25% of your legs would be a death sentence. It’s not. Spiders are remarkably resilient.
Research on wolf spiders has shown that they can still hunt effectively even with only six or seven legs. Their nervous system is decentralized enough that they can recalibrate their gait almost immediately. It’s like a car that can still drive straight even if a tire is missing, though obviously, it's not ideal.
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- Running speed: They might be a fraction slower, but often not enough for a human to notice.
- Web building: Orb weavers use their legs like precise measuring tools. Losing two can make their webs look a bit "wonky," but the webs still catch flies.
- Mating: This is the one area where it really hurts. Male spiders often use specific leg movements to signal to females that they aren't food. If they’re missing the "signaling" legs, they might get eaten before they get a chance to mate.
Common insects that trick the eye
Sometimes, it’s not a damaged spider at all. Some insects have evolved to look exactly like spiders to scare off predators. This is called mimicry.
The "Spider Cricket" (Rhaphidophoridae) is a classic example. They have incredibly long, spindly legs and a hunched body. When they jump, they look like a massive spider launching itself at you. But count the legs—always six.
Then there are the "Hangingflies." These insects often hang by their front legs and have long, dangling bodies that mimic the silhouette of a cellar spider (those "daddy long legs" types).
The curious case of the Daddy Long Legs
We have to talk about the Opiliones. These are commonly called "Harvestmen" or "Daddy Long Legs."
Here is the kicker: Harvestmen are arachnids, but they aren't technically spiders. They have one fused body segment instead of two, they don't produce silk, and they don't have venom. They are also notorious for losing legs. If you touch one, it might drop a leg immediately. Because they have such long, thin limbs, it is extremely common to find a Harvestman with only five or six legs.
Why the 8-leg rule exists in the first place
Evolution settled on eight legs for arachnids hundreds of millions of years ago. It’s a stable configuration for a predator that needs to move in 360 degrees. Most spiders are "sit and wait" or "active pursuit" hunters. Having eight points of contact gives them incredible stability on vertical surfaces and allows them to manipulate silk with their back legs while holding prey with their front ones.
If you find a spider with six legs, you aren't looking at a mutation.
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Mutations that change the fundamental body plan of an animal (like the number of limbs) are usually lethal or extremely rare. In almost 100% of cases, a six-legged spider is simply a survivor. It’s a veteran of a battle you didn't see.
What should you do if you find one?
Honestly? Leave it be.
If it’s in your house and you aren't a fan of roommates with fangs, use the classic cup-and-paper method to move it outside. You don't need to feel bad for it. Spiders don't experience "pain" the way we do, and they don't "miss" the leg emotionally. They just adjust.
If the spider is small, it might grow that leg back in a few weeks. If it’s old, it’ll carry on as a six-legged specialist.
Real-world insights for the curious observer
If you want to verify this yourself, start looking closer at the spiders you see in your garden.
- Get a magnifying glass. Or just use the macro lens on your phone.
- Look at the base of the legs. On a "six-legged" spider, you can often see a tiny stump or a scarred-over spot on the cephalothorax where the original leg used to be.
- Observe the movement. Watch how it walks. You’ll notice it doesn't limp. It has already re-wired its brain to move in a tripod-style gait or a modified crawl.
Nature doesn't care about symmetry as much as it cares about "good enough." A six-legged spider is the ultimate proof of that. It’s a creature that lost a part of itself and just kept going.
Next Steps for You:
Next time you spot a spider, don't just freak out and grab the spray. Take a second to count. If you find one with six legs, look for the "regeneration bud"—a tiny, translucent limb starting to grow back. It’s a firsthand look at one of nature’s most effective survival strategies in action. If you’re interested in the mechanics of this, look up "arachnid autotomy" in academic journals like The Journal of Arachnology; the studies on how they survive leg loss are genuinely fascinating.