I was recently asked why there were so many earthworms on the sidewalk lately. I should add that it has been raining almost non-stop for about three months and we are more than a foot over the annual rainfall average.
I thought I came up with a very likely explanation. I answered that the worms may be forced from the ground due to it being saturated with water keeping them from being able to breathe. Sounds like a great reason and it was except for one thing. It was not correct.
A little research quickly revealed that the worms come out of the ground after heavy Spring rainfall in an attempt to migrate. The moisture on the ground and sidewalk allow them to have the ability to migrate faster and farther than they could underground. Apparently they have a built in dispersal "need".
Since they require moisture on their bodies in order to breath, the ground being saturated is not an issue. An earthworm can stay submerged in a glass of water for several days without drowning.
Of course, the next question is why do they migrate?
Migration is a very common behavior in many living things. We are probably most familiar with the migration of birds, some of whom travel may thousands of miles each year. Reasons animals migrate include moving for better climates, to return to breeding areas or following food sources. The migration can be back and forth with the seasons or it can be just in one direction.
With earthworms it may be an advantage to migrate from an overpopulated community or advantageous to find a better living spot. Even though they can only travel a short distance, sometimes that can be enough to end up in a much more acceptable spot. There could be more and better food, more dependable moisture, less predators or other factors.
It is an interesting issue from an evolutionary view. The migration itself is fraught with danger for it often takes place in daylight where the earthworms are exposed to predators such as birds. The rewards from finding a better environment must out weigh the factors of mortality loss from predators, exposure to the sun or dry areas and the fact that some find a worse environment for survival. Obviously their strategy works for there is not a shortage of worms.
As a side note to this information, let me add a little tidbit.
Whether we are talking about nature or any other topic, one positive result of learning facts is being able to use those facts to deduce answers to new questions. That is part of how science works. You may have a question. Then you may make come up with an explanation or a hypothesis. Then you test that explanation/hypothesis and if you determine the hypothesis is correct, you may develop a theory. Through time the theory is tested to see if the hypothesis holds up to scrutiny.
In this case, my testing of the explanation was to use the Internet shortcut, Google. There I found the answer that I gave in the beginning of this note. Since I did not find any real scientific study that actually gave evidence to the theory that heavy rain in the Spring result in migration with worms, I cannot advance it to theory status. To do that, I would need more observational and experimental study.
At some point, I may write more on how scientists work and give a better example of exactly what a theory is. Theories are the foundation of all scientific studies. Unfortunately most people have a serious misunderstanding of the definition of a theory. They believe that a "theory" is a synonym of "hypothesis". That is definitely not the case. As with the example of the worms and the Spring rain, you can see the difference between a hypothesis and a theory. Theories are developed only after much testing of possible explanations. Theories are not guesses or suppositions. Theories are based on facts produced by observation and testing to give reliable (and testable) answers to life's questions. Nothing becomes a theory until it can be supported by the evidence using scientific methods. Again, I will say that most people do not understand this.
Probably nowhere is the word theory most misunderstood than when discussions turn to evolution. At some point, I will talk more about evolution and theories. Until then, I am grabbing my camera and am going to see what presents itself to me today.
Michael is a former biologist and Texas Master Naturalist. Originally from Newsome, Texas (Between Pittsburg and Winnsboro), educated in Dallas & Garland schools, then off to the University of Texas system where he received a degree in biology and worked as a biologist with the University of Texas system. After many years away from nature and biology, he relocated to the banks of Lake O' the Pines where he has been rediscovering the joys of nature. He is somewhat surprised that he has become a birder. Most of his interest in nature was centered around reptiles. Perhaps just like birds evolved from reptiles starting in the late Jurassic, he has begun his own evolution. During his formal education, his interests in biology/nature grew to include community ecology and population studies, all with a binding of evolutionary processes. He liked birds, but they were secondary at best. All at once he finds them fascinating.
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