If your childhood was anything similar to mine, then you will have fond memories of heading to the beach and picking up every single rock you came across to see what kind of cool things lived underneath. One of my favourite things to scavenge for were those little (but sometimes BIG) crabs that would scuttle out from under those rocks and quickly scurry to find another hiding place. I felt like a kid again when in my Experimental Biology of Invertebrates Lab (BIOL 326) we were given the opportunity to design our own lab to test something about crab behaviour and biology. My lab partner Ondine and I decided to experiment with the instinctive reaction in crabs to scurry away from any potential danger, which is considered a common prey flight response. We wanted to discover if crabs actually know where they are going when they scurry away, and if they can tell if a certain route will be successful to them or not. Basically, we wanted to know if crabs have any sort of spatial awareness or if they just panic and run in any direction just to get away.
For our experiment we used the green shore crab (Hemigrapsus oregonensis), collected from a previous field lab, and an impressively designed habitat setup using a tank, paper towels, cardboard, tape, sand, rocks, seaweed and sea water. We split our tank into two halves, one bare and bright (not very inviting to crabs), and the other filled with sand, rocks, seaweed, and blocked from light (a much more suitable environment). In between the two environments we place a cardboard barrier with two holes cut into it, one door obviously too small for the crabs to fit through, and a door large enough for them to fit through. We placed an inch of sea water in the bottom of the tank so that the crabs on the bare and bright side would be able to smell and sense the presence of seaweed on the opposite side of the barrier in order to be attracted towards it. We then placed each individual in the middle of the tank, stimulated it with a predatory poke (using a pen) periodically, and observed which door it attempted to move through.
We determined that most crabs did choose the bigger door preferentially over the obviously too small one. Therefore it is possible that crabs are spatially aware of themselves and their surroundings, and do not just scurry randomly in any direction. But curiously, we also discovered that most crabs exhibited a left-handedness and tended to move directly to the left hand side of the tank as soon as they were placed into the tank. As Beyonce would say “To the left, to the left!”, and that is just what the crabs did.
If you are interested in learning more about handedness in the green shore crab, Adam Harding experimented with handedness in their feeding habits.