Did you ever wonder why bass attack plastic worms? It's not because worms make up a significant part of a bass' diet. Worms, notably earthworms, are not aquatic animals. Instead, they live on land burrowing through the soil. As fairly lousy swimmers, worms don't make a point of frequenting local water holes for a cool dip. Worms do sometimes wash into a lake or stream following a heavy rain, but their presence in water is not the norm. A bass could go its whole life without seeing one. Moreover, we have shown in the Berkley lab that bass do not need experience with real worms to appreciate the plastic versions. Even totally naive bass; those with no natural food experience; will eagerly attack real or plastic worms on first sight.
Why do bass strike shapes they have never seen and that resemble no natural prey? In a word, the answer is instinct. Bass are predisposed to seek objects with the long body style of prey fish like minnows or shad. Other anatomical details, such as surface markings or the placement of appendages, likely play a secondary role.
One common mistake among bass anglers is the belief that natural prey shapes make the best strike releasers. Many anglers search out lures with the most natural appearance or simply use live bait believing that the best lure to offer bass is what they normally eat. This concept ignores how bass are built. Bass don't evaluate lures according to the naturalness of their shapes. Natural is a human term, not a bass term. Instead, bass evaluate lure shapes according to how well they fit pre-established visual criteria. Whether the shape is natural is of no consequence. Anglers would do better to focus on the features of shape that activate strike behavior, and then exploit those features for greater effect.
Though little work has been done on bass specifically, research on fish vision has helped define the probable limitations of bass shape analysis. For example, fish easily distinguish between targets oriented horizontally or vertically, though they find it more difficult to distinguish those placed at a 45-degree angle. Fish can also tell the difference between squares and diamonds, parallel versus nonparallel lines, and straight versus curved lines, but they have difficulty distinguishing between triangles and pie-shaped wedges. Some species are known to be more attentive to size differences along the horizontal rather than vertical axis; other species are probably the opposite.
Biases such as these certainly make sense for our bass that feed principally on long, horizontally oriented prey fish.