A continuus degree of polimorphism exists in the Iberian Messor species. A group of species (Messor celiae, Messor hispanicus, Messor lobicornis) can be named as monomorphic, as the size of the workers is quite similar to the variation know in Messor. Another group (Messor barbarus, Messor bouvieri, Messor capitatus, Messor marocanus, Messor structor, Messor timidus) is clearly polimorphic. But, as usual happens in Nature when we're trying to dicotomyze reality, there's one species (Messor lusitanicus) with a polmorphism in the middle of these two groups. The degree of polimorphism is a valid characteristic in species diferentiation for some pair of species.

In order to achieve a reliable identification it is advisable to use workers of all sizes.