16/08/2025
It’s well known that Hermit Crabs have to swap shells when they outgrow their old ones.
In certain circumstances - a chain of crabs will gather together, line up in size order, and then all at once swap shells as the larger in the line becomes vacant.
It is thought that this process is controlled through pheromones, which are chemical signals that communicate with members of the same species. Often excreted through urine, these pheromones tell nearby crabs that there might be a new shell on offer.
If you haven’t seen this incredible phenomenon, please do look it up, it’s banging - however this amazing collective behaviour isn't the norm. In a pre-plastic world hermit crabs would quite happily pootle around until they found suitable habitation. This is a long-winded job for the crabs and chemical signals remain incredibly important to the process, with often grim consequences.
Plastic buckets and bottles, washed up on beaches are potential death traps for hermit crabs.
A crab in search of a new shell might quite reasonably wander into a plastic container, but sadly, on finding it inappropriate would be unable to get a grip on its smooth sides and become trapped. Soon dying of dehydration, the deceased crab’s body releases another chemical beacon, telling hermit crabs that their shell is now vacant (on account of them being dead).
These unsuspecting hermit crabs, expecting a shell, and maybe a meal, now also topple into the plastic container and are themselves stuck.
On goes the cycle.
In the Journal of Hazardous Materials, Dr Alex Bond found that across two immensely remote islands, Cocos and Henderson, over 570,000 hermit crabs died unnecessarily due to plastic waste.
The pain of using less plastic doesn’t seem so bad now right?