Many animals remain in place most of the year and then suddenly get up and move around in mini-migrations. Today it was the harvestmen... http://en.wikipedia.org/wiki/Harvestman. The bike trail up through the Great Meadow at UCSC is where I notice the "migrations," mostly because I am moving so slowly that I actually see things. Along some segments of the trail there was one of these Opiliones stumbling across the path every meter or so. In the Fall I have noticed Thysanurids (Silverfish) on the trail in large numbers around sunset on warm days and Jerusalem Crickets after the first rains. And last summer I counted seven Alligator Lizards on one bike ride... when usually I see none.