What is a spider?

Most people think they know the answer to this question, but when challenged they usually say more about what a spider is not. Like, it's not an insect, or not what you want to find in your lunch. So here's my attempt to say what a spider really is.

A spider is an eight-legged critter that eats other critters. Where the term ‘spineless’ is considered a bit of an insult for humans, for spiders it would be perfectly normal because they don’t have a spine at all. Instead, they carry their squishy bits around inside a hard armour-like skin called an exoskeleton.

Now, apart from the bit about having eight legs I could have been describing a lot of other critters, including several insects here, so I’ll now mention some more things that make them different from insects.

You'll see in the cartoony pictures above that the spider doesn't have wings. That means spiders can't fly, although some of them do manage tricks which allow them to either glide or be carried by the wind. You'll also see that the insect has its body divided into three main bits (head, thorax and abdomen) while the spider has only two bits. That's because the spider's head and thorax are combined into one section called a cephalothorax.

And here's another thing about spiders: they're not able to chew their food.

Outgrowing their skins

I mentioned earlier that spiders wear a tough skin called an exoskeleton to hold their soft bits together. That system works well for spiders but it has its limitations too. The exoskeleton is not able to keep expanding as the spider inside it gets bigger. So as a spider grows up it sometimes has to produce another skin and shed the old one. The picture below left shows the discarded skin of a Huntsman spider.

Discarded spider skins are more interesting than most people realise. If you look at the close-up picture alongside it you'll see that it's covered with lots of stuff like hairs and spines. So the spider sheds a lot of stuff with that skin. Of course I made sure there wasn't a spider wearing the skin before I picked it ups. When you see the size of its fangs you'll get a better idea why.

The bits that bite

Spiders have fangs which can inject venom. Despite that fact, most spiders are not dangerous to people. However, because some spiders can be dangerous I advise people to treat all spiders with caution, especially if you have trouble knowing which ones are the most venomous.

Venomous or poisonous?

You might have noticed that I said that spiders inject venom from their fangs. That's why spiders are described as venomous instead of poisonous.

Now I could get into a bit of trouble here because this subject is complicated, but a rough guide goes something like this: something is considered poisonous if it's dangerous to eat it. For example, many types of wild mushrooms are poisonous.

And a critter is considered venomous if it puts venom into you by either biting or stinging.

Bad reputation

Some of the spiders which have bad reputations don't deserve them. For example, the Daddy-longlegs Spider (picture below) is sometimes claimed to have the deadliest venom in the world, and the story goes on to say that it's unable to inject that venom into people because of its small fangs. Well I've been bitten by a Daddy-longlegs Spider and it sure didn't kill me. So how did the story start?

I've heard a theory about how they got their bad reputation and it goes like this: Someone might have seen a Daddly-longlegs eating a Redback. We know that Redbacks are dangerous, so therefore it was assumed that if it beat a Redback in a fight then it must be even more dangerous.

And that would be a great example of bad logic.

You see, a Daddy-longlegs has an advantage over a Redback because it has longer legs. It can use those long legs to hold the Redback at a distance which prevents the Redback from biting it.

• So, what’s with this ‘Nature Stuff’ then?

Birds

• Indian Mynahs — pushy and invasive
• Noisy Miners — aggression in the suburbs
• Starlings — Another feral pest, or not?
• Australian White Ibis — conservation takes a twist
• Common water birds around Sydney
• Pacific Black Ducks
• Geese teeth — do birds have teeth?
• Rainbow Lorikeets — raucous and colourful
• Sulphur-crested Cockatoos — beautiful birds with an awful call
• Glossy Black Cockatoos — casuarinas’ seed crackers
• Are they Crows or Ravens in Sydney?
• Black Swans — bird emblem of Western Australia
• Brush Turkeys — Cool birds, huge nests
• Darters — comfortable on land, in the air and water
• Australian Pelicans

Trees

• A few big Australian trees
• Unusual and beautiful Australian trees
• Why Australia’s giant trees might never return

Reptiles

• Lizard bite — getting more than you bargained for

Insects and spiders

• One of the longest insects in the world (photos)
• Some common Australian orb-weaving spiders
• Hunstman Spiders
• Fear of Huntsman Spiders
• Golden Orb Weaver Spiders
• How many eyes do spiders have?
• How many eyes do insects have?
• How I catch spiders (to take them outside)
• The amazing net-casting spiders
• Commensal spiders — eating the leftovers
• What is a spider? No, seriously, what makes a spider a spider?
• Jumping spiders

Other stuff

• Book review: Back from the Brink
• So what’s a feral species, really?
• Camouflaged critters — blending in to a scene near you
• Critters in the city
• Fire and the Australian bush
• Cute stuff — critters sure can look cute when they’re little
• Wildlife photography — an unhelpful guide
• Feeding wild animals — is it a good idea?
• Photo Sales — I might have that Australian nature pic you’re looking for
• In pursuit of the waterskiing duck (blog)