Ask A Scientist Zoology Archive

name         Becky G.
status       student
age          12

Question -   We live in the midwest and have a problem with earthworms
crawling into our swimming pool.  Why do they do that?  After a really
bad rain we can have over a hundred, but in the morning following a dry
night we'll have about 10.  Is there any thing that we can put along the
border that will make them stop crawling to the pool?
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I am sorry that I cannot tell you how to keep the earthworms out of your 
pool.
I can tell you that earthworms come to the surface at night, especially
after rain soaks their underground burrows, and they may go to your pool
because they are attracted to the water, or maybe just crawl in by accident.
Maybe a pool maintenance or supply company could help you with keeping them
out.

J. Elliott
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Becky,

Long periods of rain or very water soaked soil will bring the 
earthworms to the surface.  The reason seems to be related to 
the fact that they breathe 
through their skin, and the process of diffusion of oxygen is not 
efficient enough when the ground is soaking wet.  Water does not 
hold the amount of oxygen as does the air.  Earthworms need aerated 
soil for this reason; they actually help aerate the soil with their 
continuous tunneling.  When they get to the surface under these very 
wet conditions, they often find that their is a great deal of water 
on the surface as well and they tend to move around probably seeking 
drier areas for better oxygen diffusion, it is believed.  There have 
been some studies to confirm this idea.

Now when they move around they do not have anything but the ability 
to detect light.  Light is something they avoid.  During the daylight 
period, this may add to the reason they move around; seeking a dark 
area.  Daylight is a dangerous thing!  Remember the early bird gets 
the worm?  Earthworms normally come out at night for it is dark, they 
mate on the surface exclusively because it is difficlut to find mates 
underground.  Normally, however, you will not find the earthworm moving 
around to any great extent at night.  

I have no idea how your swimming pool is designed.  I would hypothesize 
that it does not have a lip around the perimeter of the pool for these 
worms would have a difficult time climbing over it.  The pools in my 
area do not see earthworms because they all have this feature.  If you 
do, then there is something else involved.

You could purchase from a garden center some rounded edging that would 
help this situation.

Now, there is one thing you must re-think.  Earthworms are as far as 
being a pest as a organism can be.  They are very helpful in providing 
nutrients to the soil, help increase the amount of soil and serve by 
their presence to indicate that the soil environment is in good condition 
at least.

I hope I have helped.

Steve Sample
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