I’ve been trying to find a good method for quantifying just how spiny any given ant species is. Among *Pheidole* ants, we see this interesting phenomenon where certain clades have developed elaborate spines and armature relative to the rather conservative morphology of their relatives. This ‘spinescent’ morphotype has evolved independently in at least four *Pheidole* lineages.

Morphometric measurements from vector images from Eli Sarnat on Vimeo.

So how to measure spinescence? Ideally we’d have 3D tomography of representative specimens from each species, but that’s not very feasible. Using a stage micrometer to measure spine length relative to something like head width is another option, but it is really difficult to account for the curves and bifurcations in some of the structures.

My solution is to create a spinescence index, defined as the ratio of spine perimeter to body perimeter. In other words, what percentage out the specimen’s 2D perimeter is devoted to spines? It’s not a perfect solution, but it’s the best I’ve come up with in terms of accuracy and feasibility.