[Hermit] "Crabs are always looking to move into a bigger, better shell,
but having really nice digs also comes with risks. Sometimes crabs gang
up to pull an inhabitant out of an especially desirable shell. If they
succeed, the shell is quickly claimed by the largest gang member,
leaving another open shell for a slightly smaller crab to grab, and on
down the chain until everyone has upgraded.
To better gauge the trade-offs between shell size and defensibility,
Laidre collaborated with an engineer to create the hermit crab eviction machine, a device that holds onto an occupied shell and measures how
much force it takes a scientist to pull the crab out (crabs are not
harmed or left homeless). It’s essentially a portable load cell that can survive the sun, sand, and humidity of the field.
The force required to evict a hermit crab is an important measurement,
because hanging on to their homes is a matter of life and death for
crabs. “If you are evicted, there’s a real strong probability that what
is left at the end of one of those chains is something that’s too small
for you to even enter,” Laidre says. In his field area on a beach in
Costa Rica, a homeless crab can quickly succumb to predators or heat: “You’re really dead meat in a sense.”
https://www.technologyreview.com/2024/10/23/1105196/animal-mind-diy-tech-scientists-hermit-crabs-jumping-spiders/
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