Spiders quick facts
- Spiders are arachnids, not insects: eight legs, two body parts, no antennae and no wings.
- 53,244 spider species have been named so far, in 136 families, and the number rises every month.
- The world’s spiders eat 400–800 million tonnes of prey a year, comparable to all the meat and fish humans eat.
- Spiders cannot straighten their legs with muscles. They pump fluid into them under pressure, which is why dead spiders curl up.
- Nobody has died from a Sydney funnel-web bite since antivenom was developed in 1981.
There is a spider within a few metres of you right now. Probably several. They are in the corners of rooms, under floorboards, in the garden and in the grass, and almost all of them are entirely uninterested in you.
Spiders are also doing something enormous. Scientists worked out in 2017 that the world’s spiders eat somewhere between 400 and 800 million tonnes of insects and other small animals every year. For comparison, all the people on Earth together eat roughly 400 million tonnes of meat and fish. Spiders match us, and they do it without anybody noticing.
A spider is not an insect
This is the fact worth getting right first, because it explains almost everything else about them.
| Spider | Insect | |
|---|---|---|
| Legs | 8 | 6 |
| Body parts | 2 | 3 |
| Antennae | None | Two |
| Wings | Never | Usually |
| Eyes | Usually 8 simple eyes | Two compound eyes |
Spiders belong to a group called arachnids, alongside scorpions, ticks and mites. Arachnids and insects split apart hundreds of millions of years ago, so calling a spider an insect is a bit like calling a bat a bird.
As of August 2025, scientists have named 53,244 spider species in 136 families, and the list grows every month. The real total is certainly higher, because plenty of small tropical spiders have never been described at all.
How a spider is built
A spider’s body is in two parts. The front section carries the eyes, fangs, mouth and all eight legs. The back section holds the gut, the heart, the breathing organs and the silk glands.
Now here is the strange part, and it is the fact that surprises people most. Spiders cannot straighten their own legs with muscles. They have muscles to pull a leg in, but not to push it out. To extend a leg, a spider pumps body fluid into it under pressure, like a tiny hydraulic machine.
That is why a dead spider is always curled up. Once the pressure stops, the legs fold. It is also why a spider that has lost too much fluid cannot walk properly.
A few more oddities of spider anatomy:
- Their blood is blue. Spiders use a copper-based chemical called haemocyanin to carry oxygen, where we use iron-based haemoglobin. Copper turns blue rather than red.
- They taste and smell with their legs and feet, using tiny sensitive hairs.
- They cannot eat solid food. A spider injects digestive juices into its prey, waits for the insides to turn to liquid, then drinks it.
- They grow by moulting. A spider’s skeleton is on the outside, so to get bigger it must split the old one open and climb out, soft and defenceless, until the new one hardens.
Silk is the real superpower
Spider silk is one of the most remarkable materials on Earth. Weight for weight, dragline silk is around five times stronger than steel, and it stretches before it snaps, which steel does not.
Be careful with the way that claim is often written. A steel cable is stronger than a strand of silk, because it is much thicker. What silk wins on is strength for its weight, and on toughness, which measures how much energy a material absorbs before breaking. On toughness, silk beats almost everything humans make.
The record holder is Darwin’s bark spider from Madagascar. Its silk is the toughest biological material ever measured, more than ten times tougher than Kevlar, and it uses it to sling webs across rivers on bridge lines up to 25 metres long. The webs themselves can reach nearly 3 square metres, big enough to catch bats.
A single spider can make several different kinds of silk from different glands: sticky capture silk, tough dragline silk, soft silk for wrapping eggs, and fine silk for wrapping prey. The Natural History Museum explains what spider webs are made of in more detail.
Spiders can fly, and they use electricity to do it
Small spiders travel by ballooning. The spider climbs somewhere high, points its abdomen at the sky, releases fine silk threads and lifts off. Spiders have been found kilometres up in the air and hundreds of kilometres out to sea.
For a long time everyone assumed wind did the work. Then researchers showed in 2018 that spiders can detect the Earth’s natural electric field with the hairs on their legs, and will balloon in completely still air. The silk threads pick up a charge and are pushed away from the ground, exactly like two magnets repelling. Spiders are flying on electricity.
How a Spider Flies
- Climb The spider climbs somewhere high.
- Aim It points its abdomen at the sky.
- Release It lets out fine threads of silk.
- Charge The threads pick up an electric charge and are pushed away from the ground.
- Lift off The spider floats away, sometimes kilometres up.
Half of all spiders never build a web
Webs get all the attention, but roughly half of spider species hunt without one.
- Jumping spiders stalk prey and pounce, using the best eyesight of any spider.
- Wolf spiders chase prey down on foot.
- Crab spiders sit motionless in flowers, camouflaged, and grab whatever lands. Some can slowly change colour to match the petals.
- Trapdoor spiders build a burrow with a hinged lid and burst out as something walks past.
- Net-casting spiders hold a small silk net between their front legs and throw it over passing insects.
- Diving bell spiders live underwater, carrying a bubble of air trapped in body hairs.
Jumping spiders can see better than you would believe
A jumping spider has eight eyes arranged in four pairs, and each pair does a different job. The two big forward-facing eyes give sharp colour vision through a long tube inside the head, with a retina the spider can physically move around to scan a scene, like sweeping a torch across a dark room. The side eyes give wide, motion-sensitive vision covering nearly all the way behind it.
Some species see ultraviolet light, which humans cannot. For an animal with a brain the size of a poppy seed, this is extraordinary equipment.
Hunters Without Webs
- Jumping spider — Stalks its prey and pounces
- Wolf spider — Chases prey down on foot
- Crab spider — Sits still in a flower and grabs what lands
- Trapdoor spider — Bursts out of a burrow with a hinged lid
- Net-casting spider — Throws a small silk net over passing insects
- Diving bell spider — Lives underwater with a bubble of air
Eggs and baby spiders
Most female spiders wrap their eggs in a silk sac, holding anywhere from a handful to over a thousand eggs depending on species. Some hide the sac, some guard it, and wolf spiders carry it attached to the body and then let the hatched spiderlings ride on their back for a week or so.
Baby spiders are called spiderlings, and they hatch as tiny complete spiders rather than as grubs. There is no caterpillar stage, because spiders do not go through metamorphosis the way butterflies do. They simply moult and get bigger.
Most spiders live about a year. Some tarantulas are the exception: females of certain species can live over 20 years, and a wild trapdoor spider in Australia, known to scientists as Number 16, lived to 43.
Spider Record Breakers
- Darwin's bark spider — Makes the toughest natural material ever measured
- Bridge lines — Up to 25 metres long, slung across rivers
- Female tarantulas — Can live for more than 20 years
- A wild trapdoor spider — Was tracked in Australia until it was 43
- An egg sac — Can hold more than a thousand eggs
How dangerous are spiders, really?
Nearly all spiders have venom. Only one family, the Uloboridae, has lost its venom glands entirely. But venom is for catching prey, and out of more than 53,000 species, only around 25 to 30 are considered medically dangerous to people.
The ones usually named are the Sydney funnel-web and its relatives in Australia, the Brazilian wandering spiders of South America, black widows and their relatives, and the recluse spiders.
Here is the fact that should reassure you most. The Sydney funnel-web is often called the deadliest spider in the world, and an antivenom was developed in 1981. Since then, no one has died from a funnel-web bite. Not one person in more than forty years.
Almost everywhere in the world, spiders are far more useful to you than dangerous. In Britain and Ireland, no native spider can do you serious harm. If you are worried about a bite, MedlinePlus has clear medical guidance on spider bites, and our guide to black spiders with red markings covers identification.
Things people get wrong about spiders
- “You swallow eight spiders a year in your sleep.” Completely made up, and nobody knows where it started. Even the popular story about who invented it turned out to be made up. A sleeping human breathes, snores and radiates heat, which is exactly what a spider avoids.
- “Spiders are insects.” Eight legs, two body parts, no antennae, no wings. Arachnids, not insects.
- “Daddy long-legs are the most venomous spider but their fangs are too short.” Wrong twice over. The name is used for several different animals, and cellar spiders have been tested: their venom is not dangerous to humans and their fangs can pierce skin.
- “Spider silk is stronger than steel.” True only for weight-for-weight strength. A steel cable is far stronger overall because it is thicker.
- “All spiders build webs.” About half hunt without one.
- “Tarantula bites kill people.” No tarantula bite has ever been proven to kill a person. Their main defence is flicking irritating hairs.
Ten spider facts worth remembering
- Spiders eat 400 to 800 million tonnes of prey a year, similar to all the meat and fish humans eat.
- There are 53,244 named spider species, and the number rises every month.
- Spiders cannot straighten their legs with muscles. They use fluid pressure.
- Spider blood is blue.
- Small spiders fly by ballooning, using the Earth’s electric field as well as wind.
- Darwin’s bark spider slings webs across rivers on lines up to 25 metres long.
- Nobody has died from a Sydney funnel-web bite since antivenom arrived in 1981.
- Spiders taste and smell through their feet.
- Some crab spiders slowly change colour to match the flower they are hiding in.
- Diving bell spiders live their whole lives underwater inside a bubble of air.
Some of the most spectacular spiders live in tropical forests. See more in our guide to the animals of the Amazon rainforest, and the Smithsonian has a good collection of strange but true spider facts.
Spiders: Fact or Myth?
- Spiders have blue blood.
- Tarantula bites have killed lots of people.
- Spiders taste and smell with their feet.
- Daddy long-legs are the most venomous spiders, but their fangs are too short.
- Baby spiders hatch as tiny complete spiders.
- Spiders chew their food.
- Dead spiders curl up because their legs work by fluid pressure.
- A strand of spider silk is stronger than a steel cable.
Common questions
How many legs does a spider have?
Eight, always, arranged in four pairs on the front section of the body. Insects have six.
Are spiders insects?
No. They are arachnids, along with scorpions, mites and ticks. Spiders have eight legs, two body parts and no antennae or wings.
Do all spiders have venom?
Nearly all. Only the family Uloboridae has no venom glands. But venom is for catching prey, and only around 25 to 30 species out of 53,000 are dangerous to humans.
What do spiders eat?
Mostly insects and springtails. Larger species also take lizards, frogs, fish and occasionally small birds or bats. They drink their food as liquid rather than chewing it.
How long do spiders live?
Most about a year. Female tarantulas can live over 20 years, and one wild trapdoor spider in Australia was tracked to the age of 43.
Why do spiders curl up when they die?
Because they push their legs out using fluid pressure rather than muscles. When the spider dies the pressure drops and the legs fold in.
Did you know? Spiders can fly. Small spiders release silk threads and float away, and researchers showed in 2018 that they sense the Earth’s electric field with the hairs on their legs and will take off even in completely still air.
Try it
Find a spider web outdoors and look at it closely without touching. Can you spot which threads are the strong spokes and which are the sticky spiral? The spider walks only on the non-sticky ones.
Knowledge check
What makes a spider different from an insect?
Show answer
A spider has eight legs and two body parts, with no antennae and no wings. An insect has six legs, three body parts and usually wings. Spiders are arachnids, like scorpions and ticks.
Is it true that you swallow eight spiders a year while asleep?
Show answer
No, that is completely made up, and nobody knows where it started. A sleeping person breathes, snores and gives off heat, all things a spider avoids.
Frequently Asked Questions About Spiders
Is a spider an insect?
No. A spider is an arachnid, not an insect. Spiders have eight legs, two body parts, no antennae and no wings. Insects have six legs, three body parts, two antennae and usually wings. Arachnids and insects split apart hundreds of millions of years ago, so calling a spider an insect is a bit like calling a bat a bird.
How many kinds of spider are there?
Scientists had named 53,244 spider species in 136 families as of August 2025, and the list grows every month. The real total is certainly higher, because many small tropical spiders have never been described at all.
Why do dead spiders curl up?
Because spiders cannot straighten their legs with muscles. They have muscles to pull a leg in but none to push it out, so they extend their legs by pumping body fluid into them under pressure. When a spider dies that pressure stops, and the legs curl inwards.
How much do spiders eat?
Together, the world’s spiders eat between 400 and 800 million tonnes of insects and other small animals every year. For comparison, all the people on Earth eat roughly 400 million tonnes of meat and fish. Spiders match us, and almost nobody notices.
Are spiders dangerous to people?
Nearly all spiders have venom, but only around 25 to 30 species out of more than 53,000 are dangerous to humans. Almost every spider you meet is entirely uninterested in you. Nobody has died from a Sydney funnel-web bite since antivenom was developed in 1981.
How many eyes does a spider have?
Most spiders have eight simple eyes, though some have six, four or two. That is different from an insect, which has two compound eyes made of many small units. The arrangement of a spider’s eyes is one of the things experts use to identify which family it belongs to.
Sources
- World Spider Catalog, Natural History Museum of Bern — the current count of named spider species.
- Natural History Museum: what are spider webs made of? — silk types and web building.
- Smithsonian Institution: eight strange but true spider facts — spider biology and behaviour.
- The Science of Nature (2017): spiders eat 400–800 million tonnes of prey a year — the global figure quoted here.
- MedlinePlus: spider bites — medical guidance on bites.
Spider Final Challenge
- How much do all the world's spiders eat in a year?
- What do spiders mostly eat?
- How does a jumping spider's big front eyes look around?
- What do wolf spider mothers do after their babies hatch?
- How long do most spiders live?
- Of more than 53,000 kinds of spider, about how many are dangerous to people?
- Since an antivenom was made in 1981, how many people have died from a Sydney funnel-web spider bite?
- What must a spider do to grow bigger?
