Stuff To Blow Your Mind Crab Bag, Part 2: It’s Raining Crabs (Hallelujah)
Feb 26, 2026
A grab bag of crab science and culture with frog (spanner) crabs, helmet crabs, and odd carapace patterns. Lateral locomotion and how crab anatomy evolved from lobster-like ancestors. Burrowing behavior, low-oxygen adaptations, and ancient evolutionary history. Folklore tales like the Nakala and St. Francis Xavier legend. Real carrying behaviors versus myth and playful takes on crab holiness.
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Why Most Crabs Move Sideways
- Crab lateral movement evolved as many crab lineages shifted from lobster-like forward locomotion to a wider body plan optimized for sidestepping.
- Robert Lamb explains lobster-like ancestors had tails that blocked forward movement, while true crabs developed morphology for rapid lateral changes and strafing-like defense.
Frog Crabs Reversed The Typical Crab Body Plan
- Frog crabs (Raninidae) evolved a frog-like squat and paddle limbs for burrowing and front-back movement rather than lateral walking.
- Robert Lamb notes they evolved ~125 million years ago and thrived in low-oxygen periods because burrowing adaptations favored those conditions.
Crab Shell Faces Are Pareidolia, Not Fishing Selection
- Carapace patterns that look like human faces (e.g., haikagani) are likely pareidolia tied to bilateral symmetry and functional ridges, not deliberate artificial selection.
- Joe McCormick cites Joel Martin: grooves reflect internal apodemes and organs, so face-like patterns arise from functional anatomy, not fishermen’s selective release.