Scorpion

An ancient arachnid with venomous tail and pincered front claws — among the oldest land animals on Earth (430 million years), with surprising longevity and bizarre fluorescence under UV light.

Not insects, but here

Scorpions are arachnids — same group as spiders, ticks, and mites — not insects. They have 8 legs (insects have 6) and no antennae or wings. They’re included in this insects collection because of common usage; in strict taxonomy they’re separate.

Ancient lineage

Scorpions are among the oldest known terrestrial animals — fossils dating back 430 million years. They predate dinosaurs by 200 million years and have changed remarkably little in their basic body plan over that span.

They were among the first animals to colonize land, evolving from aquatic ancestors. The fossil record shows ancient marine scorpions that gradually moved to terrestrial habitats during the Silurian and Devonian periods.

Mysterious fluorescence

One of scorpions’ oddest features: they glow blue-green under UV light. The fluorescence comes from compounds in the cuticle (outer shell) — beta-carbolines and similar molecules that re-emit ultraviolet light as visible blue-green.

The function isn’t fully understood. Possible roles:

UV detection — scorpions might use the fluorescence to gauge UV light intensity (which they avoid).
Predator deterrence — possibly visible to UV-sensing predators.
Mate finding — UV signals might attract mates.

Field biologists exploit this to find scorpions at night with UV flashlights — they glow brightly even in dense vegetation.

Sting variability

Of ~2,500 scorpion species, only about 25-30 have venom dangerous to humans. The rest have stings comparable to bee or wasp stings (painful but not lethal).

The most dangerous species:

Indian red scorpion (Hottentotta tamulus) — ~40% mortality if untreated; common in rural India.
Yellow fat-tailed scorpion (Androctonus australis) — North African, dangerous.
Arizona bark scorpion (Centruroides sculpturatus) — North American, painful but rarely fatal with treatment.
Death stalker (Leiurus quinquestriatus) — Middle East, North Africa; potent neurotoxic venom.

Maternal care

Unusually for invertebrates, female scorpions display substantial maternal care. They give birth to live young (no egg stage) and the babies climb onto the mother’s back, where they ride for 2–4 weeks until their first molt. The mother defends them; some species feed them.

This level of parental investment is rare among arthropods.