I was photographing a usually submerged rock that had an unusually diverse group of mussels, limpets, and several types of barnacles all growing together on it, labelling it mentally, the “We Can Just Get Along,” photos when Meg called for me to look at a giant limpet. She was right, it was a giant, the biggest I’d ever seen. It was nestled in an alcove in the lee side of a mat of mussels, apparently enjoying their company or at least the partial.shield from the surf they provided. It was so big that it had other limpets attached to its ancient, battered shell.
Moving on I was amazed to see an even bigger brute, half again the first one’s size.
This one appeared a little more standoffish from his Mussel rockmates and was in a clear spot on the rock, unprotected from the waves, just barely touching his mussel neighbors. It too had friends along for the ride on its weathered shell. 
Well I did some research on limpets and discovered I was interpreting the scene I was looking at very wrongly. Limpets, at least of this species, are bullies. The are also territorial farmers who watch their fields of algae carefully where they grow in a clearing on the rock, defending them from others of their own species, as well as other interlopers. They graze the algae growing on their own farm/clearing in a sustainable fashion, that ensures long term productivity. But if they should stray into a neighbor’s field, they reveal their darker side and will eat everything in sight (or smell) until driven off. They accomplish this with trespassers, ramming the target with the edge of their shell followed by non-stop “shoving.”
As the tide recedes they return from their field, probably guided by pheromones contained in the slime trail they left, to their “home scar.” The combination of the contour of this “home scar,” eroded into the rock, and the limpet’s shell growing to fit its contour, helps the limpet make a better seal. When the waves return, or predators attack, this probably helps the limpet suvive until it can return to tend its field again.
Part of the field’s tending involves pushing the various molluscs that are growing at the clearing’s edge back, so they won’t shrink its size. In fact, my guess is, as the limpets grow larger, they need more food and hence spend a lot of time expanding their “empire,” pushing “trespassers and squatters” off the new farmland needed.
You might say there is a perpetual “Range War” going on right beneath our noses, but its skirmishes are fought not at High Noon, but at High Tide. Enjoy. John
