Like a bank robber armed with nothing but a banana inside a paper bag, male fiddler crabs often exaggerate the potency of their weaponry in order to bluff their opponents into submission when engaging in combat. However, according to a new study in the journal Behavioral Ecology and Sociobiology, this poker-faced sham does not always work, as smaller crabs often call the bluff of their larger adversaries, forcing them to back off.
Male fiddler crabs are famous for their lopsided hardware, boasting one enormous claw that they tend to use for fighting and one smaller claw that they use for other general crab stuff. However, it is not uncommon for the larger claw to become severed, either as a result of fighting with a rival or a run-in with a predator.
When this occurs, a new claw is regenerated, although while this replacement claw often matches the original in size, it is usually considerably weaker. As such, male fiddler crabs with regenerated claws need to use all their cunning and guile in order to increase their chances of victory in combat, and do so by playing mind games with their opponents.
According to lead study author Daisuke Muramatsu, “fiddler crab males adapt their fighting tactics and choice of opponent depending on whether they have lost their major claw.” For instance, they tend to pick on crabs with a smaller fighting claw than their own, hoping for a quick submission.
They are also careful to pick fights with opposite-handed crabs, rather than those with a fighting claw on the same side as their own. The researchers suspect they do this because fiddler crabs find it harder to assess the strength of an opponent when their fighting claw is on the opposite side, as they cannot interlock as easily.
Crucially, fiddler crabs appear unable to distinguish between original and regenerated claws by sight alone, making it possible for those with regrown claws to convince others that they are packing more of a punch than they in fact are.
Some fiddler crabs are all claw and no fling. duangnapa_b/Shutterstock
This bluff tends to occur in the first phase of fiddler crab fighting, known as the contact stage. Like a kind of crustacean weigh-in, this part of the contest sees the crabs compare claw sizes in order to determine if they are evenly matched, with each combatant trying to psych their opponent into retreating, much like boxers talking up their punching ability at a pre-fight press conference.
This is followed by what the researchers call the interlock stage and the fling stage, each of which carries a greater threat of injury than the last. It is in the interests of crabs with regenerated claws to avoid such an escalation, although unfortunately for them, those with original claws are fully aware of this.
As such, they employ shrewd counter-bluff tactics, often forcing their larger adversaries to engage in full combat. Additionally, they tend to pick fights with same-handed crabs as themselves, knowing that if their rival’s claw is a regrown one, he will most likely surrender before reaching the fling stage.
Because of this, the researchers found that males with original claws defeated those with larger regenerated claws in 42.9 percent of observed cases, with one particularly gutsy crab picking on – and beating – another with a regenerated claw that was 42.7 percent larger than his own.
Overall, the results of this study emphasize the ability of fiddler crabs to adjust their fighting tactics in response to their own changing physical condition, craftily selecting their opponents in order to win the mental battle without having to engage in actual combat.