Why Do Fish Eat Worms?

     While waiting for school to start today my daughter noticed my fishing gear by the door and said, "Why do fish eat worms?"  I just kind of laughed it off and answered, "because their hungry."  I loaded up the gear in the truck, dropped her off at school, then headed to the lake.  A few casts into the morning, and my brain wouldn't stop replaying the question.  So why do fish eat worms?  Not just a couple fish, but almost every freshwater fish I can think of eats worms.  Bass, bluegill, crappie, catfish, trout, pike, walleye, the list goes on and on.  Now I know the evolutionary basics about earthworms.  I also know that they are terrestrial, meaning they don't live in water on purpose.  Sure they might occasionally get washed into the water during a heavy storm or maybe dropped into the water by a clumsy bird, but that would mean that fish generally wouldn't have them as a prey item.  So why do fish eat worms?

     After a lot of thought I came up with 3 ideas.
  1. They come into regular contact with a similar prey item.
  2. Something about the worm attracts/triggers them to eat.
  3. Worms are simply delicious!
     The first idea is the question I most wanted an answer to.  Do they eat something regularly that's similar?  After some research I discovered that they do.  Limnodrilus hoffmeisteri is a relative of the earthworm.  They have many similar traits to their terrestrial cousins, but they also have a very distinct difference.  Limnodrilus hoffmeisteri lives in water, not on land.  They commonly inhabit freshwater streams, rivers, marshes, and lakes.  Turning over rocks or digging in the muddy bottom is usually all you need to do find these guys.  They are so plentiful that many times they are the most abundant animal in the water.
     To answer the second question, we need to look at a few ways fish find prey.  The most common is sight feeding.  When a worm is placed on a hook it wiggles, I would too.  A lot of fish in freshwater have very good eyesight.  Frantic wiggling looks like something trying to get away to a fish, that in turn triggers a predatory response.  The worm unknowingly screams I'm out here EAT ME.  Another common way fish find prey is through the use of their lateral line.  The lateral line is a sensory system that allows the fish to detect weak water motions and pressure gradients.  In layman terms, this series of cells lets the fish find food based on vibrations in the water.  They don't have to see it, they can feel that something is there.  So when Mr. Wiggles on the hook starts gyrating around, the water in turn moves, and that triggers the fish to bite.
     This brings up my third idea, worms are just plain delicious.  Ever tear a worm in two to bait a hook?  Notice anything? Like maybe they are all meat.  Sure they have a nervous system and digestive tract, but they don't have much else.  We all know that proteins are the easiest thing for most predators to digest.  We also know that most proteins taste good.  I have yet to find a steak I wasn't a fan of, and I believe fish are the same way.
     Hopefully this helps to answer the question.  I'm gonna have to thank my daughter for the inspiration behind this post.  I must admit that for all the times I have used them as bait, it never once occurred to me to ask why the fish eat them.  Kind of makes me wonder why some of my other baits work so well.  Do you have anything to add to this discussion?  Maybe a question you would like answered?  Leave a comment below.
     Tight Lines.

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