Some arthropods get more love than others. If you asked people to personally rank arthropods on a scale of “Aw, it’s pretty cute” to “Get that thing away from me,” I’d bet that most arachnids would fall off the ranking entirely and land in the “Burn that thing with fire” category. There are some arachnids even I don’t like – I’ve handled tarantula escapees, been personally accosted by katydids and praying mantids, and stuck my hand in centipede tanks – but nothing compares the bone-chilling, stomach-dropping nightmare fuel that are… ugh… ticks.
But, I am a firm believer that the more you know about something, the less scary it seems. There are some pretty alien-like animals in the arachnid class (Arachnida), and they deserve our love, no matter how weird or repugnant they might appear. So I’m devoting the entire month of April to arachnids; from their impressive diversity, to their phobia-inducing mythos. But first, what exactly is an arachnid?
If some of these words – arthropod, order, arachnida, class, phylum – are throwing you for a loop, don’t fret. Taxonomy can be confusing; I constantly have to look up arthropod phylogenies (“family trees”). So if it’s been a while since your last biology class, here’s a quick refresher:
Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species
All animals belonging to the phylum Arthropoda (arthropods) are invertebrates; that’s animals with an exoskeleton. Arachnids are further divided into the subphyla Chelicerata, then the class Arachnida. They are further subdivided into orders. We will be discussing arachnid orders like Aranae (true spiders), Scorpiones (scorpions), and Ixodida (Ticks), among many others.
Anatomy of an Arachnid
Like all arthropods, arachnids have a hard exoskeleton. They undergo a similar growing process; they have to molt, or shed their old exoskeleton, in order to grow larger.
All arachnids have 8 legs. Okay, most arachnids have 8 legs. Unlike insects, they do not have wings or antennae, so you can put your fears of flying spiders to rest. They have 2 body segments, the cephalothorax (a fused segment of the head and thorax) and the abdomen. Some arachnids, like harvestmen, mites and ticks, give the impression of having only one body segment.
The majority of arachnids are carnivorous, but not all of them are venomous!
Each week I’ll introduce a handful of arachnid orders, share the morphological similarities and differences, dispel some myths (there’s a lot!), and provide some fun, general information detailing each type of arachnid.