Arachnids - Types & Characteristics
Arachnids, fascinating and sometimes feared, represent a diverse group within the animal kingdom. Occupying nearly every corner of our planet, from the sandy dunes of deserts to the hidden crannies of our homes, these creatures have been the stuff of legends, myths, and nightmares.
Yet, the world of arachnids is so much more than the stereotypical spiders that come to mind. Their evolutionary success story dates back to the Silurian period, over 400 million years ago, and today they count among some of the most versatile predators and vital players in many ecosystems.
From silk-spinning spiders to the scorpions glowing under UV light, arachnids possess a myriad of adaptations that make them compelling subjects of study and wonder.
While they may not enjoy the same popular appeal as their insect cousins, arachnids play a crucial role in controlling pest populations, recycling organic material, and contributing to biodiversity.
10 Characteristics of Arachnids
- Four Pairs of Legs: One of the defining features of arachnids is their eight legs, setting them apart from insects which have six.
- Two Main Body Parts: Arachnids have a two-parted body: the cephalothorax (a combined head and thorax) and the abdomen.
- No Antennae or Wings: Unlike insects, arachnids lack both antennae and wings.
- Chelicerae: Instead of mouthparts like insects, arachnids have structures called chelicerae. In spiders, these evolve into fangs, while in scorpions, they appear as small pincers near the mouth.
- Simple Eyes: Most arachnids possess simple eyes, which means each eye has a single lens. The number and arrangement of these eyes can vary among species.
- Exoskeleton: Much like insects, arachnids are protected by a tough exoskeleton made of chitin, which they must shed in order to grow, a process known as molting.
- Predatory Lifestyle: The majority of arachnids are predators, employing various methods to capture their prey. Spiders, for instance, often use silk to trap their victims.
- Silk and Venom Production: Many arachnids, especially spiders, possess silk-producing glands. Similarly, many arachnids are equipped with venom glands, using their venom both for subduing prey and for self-defense.
- Book Lungs or Tracheae: Arachnids breathe through specialized structures known as book lungs or tracheae, which allow for gas exchange.
- Sensory Hairs: Their bodies, especially the legs, are covered in sensitive hairs that can detect vibrations, air currents, and even some chemical signals.
The Top 6 Types of Arachnids
There are around 12 or 13 orders of Arachnids that exist on our planet. You can see here the 6 major types that you are most likely to encounter.
Spiders (order Araneae)
Spiders, representing the order Araneae, are perhaps the most recognized of all arachnids. They’re universally known for weaving intricate webs using silk produced by specialized glands.
While they do possess venom to subdue their prey, only a handful out of the 48,000+ known species pose any risk to humans. Their ecological importance as pest controllers is undeniable, making our surroundings less populated by various insects.
Scorpions (order Scorpiones)
Distinctly recognized by their curved tail and venomous stinger, scorpions are inhabitants primarily of desert and tropical regions.
Though they can appear menacing, only a small percentage of the over 2,500 known species have venom potent enough to be dangerous to humans. Their nocturnal nature makes them elusive, often seen during nighttime treks or under rocks.
Ticks and Mites (order Acari)
Ticks and mites of the order Acari are minuscule but can have a significant impact. While ticks are notorious for transmitting diseases like Lyme disease, mites can range from being plant feeders to causing skin irritations in humans and animals. Their small size means they often go unnoticed until they become a problem.
Harvestmen or Daddy Longlegs (order Opiliones)
With their slender, elongated legs, harvestmen stand out in the arachnid world. Often mistaken for spiders, they lack venom and silk-producing abilities.
These harmless creatures are frequent residents of gardens, forests, and sometimes basements, acting as scavengers and feeding on a variety of organic matter.
Sun Spiders or Camel Spiders (order Solifugae)
Solifugae, often referred to as sun spiders or camel spiders, are fearsome in appearance but are mostly harmless to humans. Common myths, especially from desert regions, exaggerate their size and capabilities.
While they don’t possess venom harmful to humans, their speed and robust jaws make them formidable predators in their habitat.
Whip Scorpions or Vinegaroons (order Uropygi)
Venturing into tropical caves might lead to an encounter with the fascinating whip scorpions, also known as vinegaroons. These nocturnal creatures, belonging to the order Uropygi, get their name from the whip-like tail they possess.
They can spray a defensive acidic liquid, which has a vinegar-like odor when threatened. While they might look intimidating, they are non-venomous and pose no threat to humans.
Frequently Asked Questions About Arachnids
Arachnids typically have eight legs, two main body parts (the cephalothorax and abdomen), and lack antennae and wings, while insects have six legs, three body segments, and often possess antennae and wings.
While most spiders produce venom to subdue their prey, only a small number have venom that’s harmful to humans.
Scorpions have certain chemicals in their exoskeleton that make them fluoresce under ultraviolet (UV) light, but the exact reason for this characteristic is still being researched.
No, only spiders and some mites produce silk. Other arachnids, like scorpions and harvestmen, do not produce silk at all.
Ticks can carry disease-causing agents like bacteria, viruses, or protozoans in their saliva. When they bite and feed on a host, these agents can be transmitted, leading to diseases like Lyme disease or Rocky Mountain spotted fever.
Daddy longlegs, or harvestmen, belong to the order Opiliones and are not true spiders. They lack venom and silk-producing glands, distinguishing them from true spiders.
No, most stories about camel spiders, or sun spiders, are exaggerated. While they are fast and have strong jaws, they are not venomous to humans and are not as large as some tales suggest.
Whip scorpions, or vinegaroons, are carnivorous predators that feed on insects, worms, and other small creatures. They use their pincers to grab prey and their chelicerae to crush and consume them.
Many mites are microscopic or very small, making them hard to notice until they become problematic, like when they cause skin conditions or damage plants.
While the majority of arachnids are carnivorous predators or parasites, some, especially certain mites, can be herbivores or detritivores, feeding on plant material or decaying organic matter.
Learn More About Arachnid Species
Links to articles packed with surprising facts and knowledge to further learn about amazing species of Arachnids, so you know what you are looking at on your next wildlife trip!