Not impressed with “coconut octopus”

A video and paper in Current Biology about a veined octopus, Amphioctopus marginatus, that carries coconut halves to deploy as a shelter has gotten a lot of play in the popular press. The story is usually accompanied by the claim that this is the first reported case of invertebrate tool use. Maybe this is true amongst the squishies (cephalopods), but I think that arthropods accomplish much more exciting feats of tool use every day.

Coconut octopus, meet coconut crab. Earlier, I talked a little about coconut crabs, mentioning that they use mollusk shells when they are small, and eventually discard them as they grow. They also have an intermediate size behavior where they use hollowed out coconut shells as a shelter. Photos: Finn et al., 2009 and Nancy and Neil.

First a disclaimer: I think cephalopods are awesome. They are probably the second coolest animal group behind mantis shrimp. Also, this video and paper represent a really interesting finding, and any antagonism in this post is meant to be humorous. I only take exception to the tool use claim. I, of course, realize that any assessment of “tool use” is completely dependent on how you define “tool use.” However, even by the researchers own exclusive definition, arthropods still beat their motile mollusk to the punch.

Let’s see how they define tool use in order to exclude the numerous arthropod examples:

…simple behaviours, such as the use of an object (or objects) as shelter, are not generally regarded as tool use, because the shelter is effectively in use all the time, whereas a tool provides no benefit until it is used for a specific purpose. This rules out examples such as the use of gastropod shells by hermit crabs, but includes situations where there is an immediate cost, but a deferred benefit, such as dolphins carrying sponges to protect against abrasion during foraging and where an object is carried around in a non-functional form to be deployed when required.

Actually, I don’t see how this definition even negates hermit crabs from tool use. There is no benefit for the crab in dragging around a heavy shell or coconut on its back while it forages. It is only beneficial later, when the animal wants to rest or block an attack. I would say that is a fairly specific deferred purpose with an immediate cost.

Regardless, there are a bunch of other examples of arthropod tool use that I can pull off the top of my head.

  • Spiders construct structurally elaborate webs as methods of defense as well as prey capture. In addition to the common trap webs, some Gladiator Spiders also make web nets that they hold in their front arms and use to pin prey to the ground.
  • Gonodactyloid mantis shrimp are capable of complex masonry work, chiseling into form and stacking walls of rubble and shells around their lairs. They strongly suggest planning capacities with this behavior.
  • The amphipod Phronima hollows out tunicate carcasses to live inside and drive around in the deep-sea in search of more prey.

Again, calling any of this “tool use” is extremely definition dependent. However, under the above interpretation, I think many arthropods have just as strong a claim to tool use as the octopus. Regardless, squishies and crunchies need to get along so that they can join their tool-using forces to protect us from those goddamn dolphins.

References:

  • Finn et al., 2009. Defensive tool use in a coconut-carrying octopus. Current Biology, 19; 1069.

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I have moved.
Arthropoda can now be found here.

Michael Bok is a graduate student studying the visual system of mantis shrimp.

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