Do Spiders Always Have Eight Legs? The short answer is yes! However, there are so many different appendages to the spider that the answer is a little more complicated.
A Spider is in a class called Arachnida. Arachnida are joint-legged animals (also called arthropods).
The type of Arachnida includes mostly spiders, but also ticks, scorpions, and mites, to name a few.
Most adult arachnids have eight legs. However, in some species, the front pair of legs are used as more of a sensory function. In other species, the different appendages get large enough to look like an extra pair of legs.
The Anatomy of a Spider
The anatomy of a spider is one of the most interesting when it comes to arachnids. There are so many parts that make up the body of this fantastic creature.
Spiders are not insects, and so they have two main body parts, called tagmata. They have a fused head and thorax (known as a cephalothorax), as well as an abdomen.
However, there are some spiders (called assassin spiders), where the abdomen is divided into parts by a long neck. But most spiders do not have this segmented abdomen. And unlike insects, spiders have an endoskeleton and an exoskeleton.
In the spider, most of its external appendages are attached to its cephalothorax, including her eyes, chelicerae (her jaw), and other mouthparts. Also attached are her pedipalps, which look like tiny walking feet and sit laterally to her chelicerae.
Spiders are unable to chew their food, so they have a part of their mouth that is shaped like a little drinking straw. They use this to drink the insides of their prey.
This is where it gets interesting. For the most part, spiders have eight walking legs; themselves made up of seven parts.
Starting from the component connected to their bodies, these segments are called the coxa, the trochanter, and the femur. We then have the patella, the tibia, the metatarsus, and at the end, the tarsus.
At the tip of the tarsus, the spider has little claws, which can vary in size. Webspinners usually have three claws, with the middle being the smallest. Spiders that hunt their food typically have just two claws.
Because spiders do not have antennae, they have equipped with sensitive setae, or bristles, on their legs. These allow the spider to pick up sounds, scents, vibrations, and air currents.
The pedipalps, which are like the little walking shoes, have six different parts. In male spiders, the tarsus is on each pedipalp and used to carry a structure used for mating called the palpal bulb.
The fundamental parts of the pedipalps are called coxae and lie next to the spider’s mouth. These assist with feeding, and in some spiders, they are saw-like and used to cut up their prey.
The cephalothorax in spiders is joined to her abdomen by something called a pedicel. This is what allows them to move their abdomen in all directions. It also allows her to spin silk without moving her body.
Towards the front of the spider’s abdomen are hard plates called epigastric plates, which cover the book lungs, a respiration organ found in arachnids.
What About a Spider’s Spinnerets? Are those considered legs?
A spider’s abdomen doesn’t really have appendages, but they do have pairs (usually three) of telescoping organs. These are called spinnerets, and they produce silk.
Before spiders evolved, their ancestors had four pairs of spinnerets. Two were on the tenth body segment and two on the eleventh body segment.
Most spiders have spinnerets toward the posterior end of their body, where a small cluster is formed. The anterior spinnerets on the tenth segment are usually formed into a flattened plate called the cribellum.
The cribellum is typically split up into two sides, and it creates an almost infinite amount of dry silk fibers that are wrapped around a thicker fiber. These are then combined into a wool-like structure by the specialized hairs (setae) on their fourth set of legs.
It is thought that the wool-like silk is charged with static electricity! This static electricity causes the fibers to attach to their prey.
However, not all spiders have a cribellum, and in some that do, it is unable to produce silk. Scientists have given it the name colulus, but have not identified what the exact function is. Spiders that do not build webs, like the jumping spiders, actively hunt their food.
So, Why Do Spiders Have Eight Legs
The simple answer is that spiders have eight legs because their ancestors did. Spiders are actually named for the snappers on their heads, also called chelicera. Some chelicera snap in, in an up and down motion, and some go sideways.
Others in the arachnid class have four pairs of legs. Horseshoe crabs, who are closely related to spiders, also have four pairs of legs. Horseshoe crabs really haven’t changed much in the hundreds of millions of years, and spiders developed from the same ancient relatives.
Do Spiders Need All These Legs?
Maybe not. Spiders are always thought of as creepy-crawly because they have so many legs. But scientists believe that spiders may have more legs than they need. Thousands of female spiders were collected in the wild, and more than ten percent were missing at least one leg!
Can They Still Build Webs?
Scientists wondered if this prevented the spiders from doing their jobs. The spiders were placed in plastic cases, so they could build a web. Only a little over half of the spiders had all their legs, which the others were missing at least one.
Scientists discovered that the spiders with missing legs seemed to have no problem building their webs.
What About Hunting?
Scientists then placed the spiders in enclosures with flies and found that the spiders with less than eight legs had no problems at all! They were able to catch and eat the insects successfully.
The scientists were impressed to see that missing a leg didn’t render the spider’s ability to hunt in the least.
So, What Was the Consensus?
While the scientists felt that spiders might have legs they don’t need, there was an advantage when it came to escaping a predator. There also seemed to be a limit to the number of legs a spider could be missing before things became difficult for them.
It appeared that there weren’t many spiders missing more than two legs, and those with five legs had difficulty building a decent web.
Is a Spider’s Mouth Considered an Appendage?
Yes and no. We always notice a spider for her eight legs. It’s the tell-tale sign of these critters. But if you haven’t looked closely, you may not have seen signs of her mouth. And they do indeed have tiny mouths.
As mentioned before, spiders can’t chew their food because they don’t have mandibles. Instead, they have their chelicerae.
If you ask me, I think the chelicerae look like little gunslinger mustaches!
These little sharp-edged jaws are actually another appendage on the spider. And yes, some of them do have fangs or pinchers.
Spiders use their chelicerae to grab and render their prey immobile because the chelicerae are attached to the venom glands. Towards the back of the chelicerae, the spider has other small parts of her mouth, called the labrum and labium. These three parts work together to get food into her mouth.
Do Other Bugs Have Eight Legs?
While spiders and insects are both arthropods, a spider isn’t an insect. Confusing, I know. But many other crawling species do indeed have eight legs.
Daddy Long Legs
There are roughly 6300 species of Daddy Long Legs! And no, they aren’t actually spiders. Aside from the slinky legs, they do not make silk, and they are not poisonous. Like spiders, though, most come out at night to hunt.
Scorpions, with over 2000 species, are identified by their whiplike tail and multisegmented body. They also have a pair of venom glands and a barb that injects venom.
Like spiders, they use pinchers (or fangs) to catch their prey. They also inject it with poison to paralyze it. They do not spin webs but instead live under holes or rocks. Unlike spiders, the scorpion can produce live young.
Ticks and Mites
I’m most creeped out by ticks, and between ticks and mites, there are over 30,000 species. Most are much smaller than spiders, none more than 1.0 mm.
These tiny eight legs creatures live in both water and land. For the most part, they are parasites, which spiders are not. They also transmit diseases to both animals and humans.
While most of the world seems to loathe the idea of spiders, they are highly beneficial to the ecosystem. And hopefully, with this article, one can understand a little more about their anatomy, specifically their legs.
Spiders are pretty fascinating creatures, but what is unfortunate for those of us who despise them is that Spiders are pretty resilient and have been around for millions of years with no signs of slowing down.
Alright, that’s it for this article, here are a few hand-selected articles that you might also find interesting reads:Why Do Spiders Have 8 Eyes? The Curious Answer
How Spiders Move and How it differs to Human
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