In reference to Horseshoe-crabs Kropotkin says: “I was struck (in 1882,
at the Brighton Aquarium) with the extent of mutual assistance which
these clumsy animals are capable of bestowing upon a comrade in case
of need. One of them had fallen upon its back in a corner of the tank,
and its heavy saucepan-like carapace prevented it from returning to
its natural position, the more so as there was in the corner an iron
bar which rendered the task still more difficult. Its comrades came
to the rescue, and for one hour’s time I watched how they endeavored
to help their fellow-prisoner. They came two at once, pushed their
friend from beneath, and after strenuous efforts succeeded in lifting
it upright: but the iron bar would prevent them from achieving the
work of rescue, and the Crab would again heavily fall upon its back.
After many attempts, one of the helpers would go in the depth of the
tank and bring two other Crabs, which would begin with fresh forces
the same pushing and lifting of their helpless comrade. We stayed in
the Aquarium for more than two hours, and, when leaving, we again came
to cast a glance upon the tank: the work of rescue still continued!
Since I saw that, I cannot refuse credit to the observation quoted by
Dr. Erasmus Darwin--namely, that ‘the common Crab during the moulting
season stations as sentinel an unmoulted or hard-shelled individual
to prevent marine enemies from injuring moulted individuals in their
unprotected state’.”