Not all eight of a tarantula’s legs are equal, according to a new study in the Journal of Zoology that suggests that, like many humans, spiders may be right-handed.
Behavioral laterality, which refers to the preference for using one side of the body over the other, has previously been reported in a number of different species, and is due to certain structural or functional specializations in either the left or right side of the brain.
To find out whether male tarantulas can be classed among the many animals that exhibit such behavioral asymmetry, the study authors placed the arachnids in a T-shaped maze with a corridor on both the left and right sides of a central chamber.
First, the team placed live cockroaches at the end of each corridor, knowing that these happen to be among tarantulas’ favorite snacks. Beginning in the center of the maze, the spiders consistently chose to travel down the right-hand corridor.
The researchers then repeated the experiment, except this time they placed female tarantulas instead of prey at the ends of the corridors. Once again, the male spiders went to the right instead of the left, attracted by the pheromones of the leggy ladies.
Tarantulas use a range of sensory apparatus to detect both prey and mates, including several pairs of eyes and hairs called trichobothria that pick up chemicals and vibrations in the air. The species used in this experiment, Brachypelma albopilosum, has four pairs of eyes, arranged in two horizontal rows.
When examining these eyes, the researchers found no difference in size between those on the right and those on the left, while also noting that eyes on both sides have the same density of photoreceptors. This means that the left and right eyes receive the same amount of light, so the spiders’ preference for sensing prey and mates on their right side must be caused by a quirk of their neural wiring, rather than any physiological attributes.
Similarly, the tarantulas were found to have the same density of trichobothria on both sides of their body, once again indicating that this right-handedness is not down to morphology, but must instead be caused by the way that the spiders’ brains decode information coming from the left and right sides of the body.