Why so crabby?

Perhaps this is the reasoning behind the colloquial phrase “bad like crab” which is often used in Trinidad and Tobago to refer to a bad-tempered person or someone who is irritable. A delve into a crab’s social side can bring light to this view.

Crabs belong to a diverse group of crustaceans known as decapods, along with lobsters, crayfish, prawns and shrimps. Their diversity is reflected by the many types of biomes that they can be found in, ranging from aquatic (marine and freshwater) to the surprisingly semi-terrestrial (forests and deserts). Aside from their addition in local dishes such as callaloo and crab and dumpling, other thoughts that may come to your mind involving .the reluctance to hold a crab, if you have ever encountered one, and the hostile reaction you receive when it is caught.

Not all demeanour of crabs are considered unfriendly but the defensive characteristics of this group make them formidable combatants in nature.

Most crab species are equipped with sharp, tough claws called chelipeds, with crushing, scissor-like power, capable of delivering a painful hold to the ad hoc handler (my personal experiences).

In most species, the male has a noticeably larger claw than the other but both are useful for the actual attack action and are often used along with the walking legs for displaying warning or threatening cues toward other crabs. Most aquatic species such as those of the marine “Cancer” genus tend to have two to three threatening postures that they use for different levels of warning.

My encounters with the local “manicou” or “mountain” crab (Rodriguezus garmani) in upper river regions of TT were met with a marked threat display which involved an outstretched posture. Males of this species often swiftly snapped their sharp claws in a forward direction when approached any further.

Talk about being crabby! An even more anti-social and eerie behaviour associated with this freshwater crab species involves cannibalism, where the victor of an initiated combat makes a meal of the loser. Interestingly, a somewhat gentler group of crabs, known as the fiddler crabs (Uca sp) rely on visual threat signals expressed as “waving”, coupled with avoidance.

These crabs rarely engage in physical contact with others, instead relying on visual cues for resolving challenges. If contact is made, the interaction usually involves pushes, taps or sometimes interlocking of claws. Male fiddlers tend to position themselves outside their burrows with the larger claw on full display; much like sentries ready to defend their keep.

Some temperate species even resort to nocturnal drumming with the claws in order to warn off approaching males, while also seeking to attract females to their burrows.

In other species, engagement in physical combat is much more common and dominant males go so far as to invite a “fight”, or battle with other males over territory and for the female crabs residing within that particular territory. So much for not having a backbone! These interactions may seem hostile from the human perspective but are considered very social and typical behaviours for crabs. These behaviours also provide indirect means of population control and allocation of food, space and mates. So, despite a person’s ill-tempered mood being fairly referenced to a crab’s demeanour, the motives behind the latter represent a far more complex and very social aspect of order, fitness and survival for these formidable, yet fascinating creatures.

For more information on our natural environment contact the Trinidad and Tobago Field Naturalists’ Club at admin@ttfnc.org or visit our website at www.ttfnc.org and our Facebook or YouTube pages.