Sheer aggression rather than pure muscle strength often gives hermit crabs living in broken shells the edge during a fight. Broken shells constrain crabs’ activities because they are heavy and a large portion of them unusable. Crabs living in broken shells value an intact shell and will fight more aggressively to get a better one. This is according to research conducted by Guillermina Alcaraz of the Universidad Nacional Autónoma de México in Mexico and Gastón Ignacio Jofre of Texas A&M University in the US. Their findings are published in Springer’s journal Behavioral Ecology and Sociobiology.