Class: Arachnida

Arachnids have evolved over 400 million years ago during the Silurian period. They have descended from an early group of arthropods known as eurypterids, or sea scorpions, which were aquatic predators. The transition from water to land was a significant step in the evolution of arachnids, requiring adaptations to new environments and lifestyles.

The development of a tough exoskeleton made of chitin was crucial for protection and support in terrestrial environments. The evolution of book lungs and tracheae allowed arachnids to efficiently exchange gases in air, facilitating their survival and diversification on land. In spiders, the evolution of silk glands and the ability to produce silk for web construction, egg protection, and prey capture was a significant adaptation. Many arachnids, including spiders and scorpions, evolved venom to subdue prey and defend against predators, increasing their survival chances.

Major Orders Within Arachnida

Araneae (Spiders): The largest order of arachnids. Known for their ability to produce silk and construct webs. Include a wide variety of species, each with unique web-building and hunting behaviors.
Scorpionida (Scorpions): Recognized by their elongated bodies and segmented tails ending in a venomous stinger. Scorpions have pincers (pedipalps) for grasping prey.
Pseudoscorpionida (Pseudoscorpions): Small arachnids resembling scorpions but without a tail or stinger. Commonly found in soil, leaf litter, or under bark.
Acarina (Mites and Ticks): Include a diverse group of mites and ticks. Mites are often very small and inhabit various environments. Ticks are ectoparasites, feeding on the blood of mammals, birds, and reptiles.
Opiliones (Daddy Longlegs or Harvestmen): Recognized by their long, slender legs and compact bodies. Unlike spiders, their body segments appear fused into a single oval structure.
Uropygida (Whip Scorpions or Vinegaroons): Characterized by a whip-like tail and the ability to spray a vinegar-like substance as a defense mechanism.
Palpigradi (Micro Whip Scorpions): Very small arachnids, typically less than 3 mm in length, found in moist environments like leaf litter.
Amblypygi (Tailless Whip Scorpions): Known for their large, raptorial pedipalps and elongated, whip-like first pair of legs. Harmless to humans despite their fearsome appearance.
Ricinuleida (Hooded Tickspiders): Characterized by a hood-like structure that covers their mouthparts. Relatively rare and not well-known to the general public.
Solifugae (Camel Spiders or Sun Spiders): Known for their large, powerful chelicerae (mouthparts) for capturing and crushing prey. Typically found in arid environments.