Arthropods: Arachnids

- Eewh, Leon look! There’s a massive spider in our tent! - Cool! I haven’t seen this one before, let me take a closer look! This spider, like all other spiders, has eight legs. The legs are made of seven sections and end with two small claws - this is why they can climb on nearly any surface, and even walk hanging upside down!

What about these things, in front of the first pair of legs? These are appendages that are used for sensing the surroundings, but also for moving around and reproducing. We call them pedipalps. If you look even closer, you can see that there is another pair of appendages in front of the pedipalps. These are the mouthparts, called chelicerae.

They’re used mostly for feeding and for defense. Legs, pedipalps and chelicerae are all found on the front part of the body, the cephalothorax. Behind the cephalothorax is the rear part of the body, the abdomen. But spiders are not the only animals with these body features! Scorpions, mites and ticks have the same characteristics - 8 legs, pedipalps and chelicerae, with bodies split into cephalothorax and abdomen.

Scorpions, mites, ticks, and spiders belong to different categories or orders that share these common features, and together form a bigger group, a CLASS, called ARACHNIDS. Although members of the arachnid class have so much in common, each order also has incredible, unique features. The pedipalps of scorpions for example are much larger than that of other arachnids and look like pincers or claws. Scorpions also have an extra body part that the other arachnids don’t have - a tail! The tail is made up of six sections, the last one being a stinger that scorpions use to inject venom into their prey.

Spiders on the other hand, have special organs called glands, that produce spider silk. They use this silk to spin webs, trap prey and form cocoons. The silk is extremely strong and has antibacterial properties. Scientists think that if they can make it in the lab, it could be used in medicine, for example, for healing wounds. Although many people don’t like spiders very much, they are actually very good to have around.

They’re not only important parts of ecosystems, but they’re also great hunters, catching insects like mosquitoes. Mites and ticks can actually cause much more harm to humans than spiders! Some types of mites live in human homes, mostly in mattresses, and a lot of people are allergic to them. Only slightly bigger than mites, ticks are parasites that can carry diseases dangerous to people and animals. - So really Michael, we should hope there are loads of spiders around tonight, to protect us from mosquitoes and other insects. - Hm, knowing all this makes me feel a bit better. Maybe I don’t need to barricade the whole tent after all.