Worms and Barometric Pressure

Interesting question from Chris:

I have 2 worm bins. One bin contains 2 lbs. of red wigglers, and the other contains 2 lbs. of African Nightcrawlers. I started both bins around the same time (last of June or early July). So far, the worms are doing great. They are even laying eggs. I have been feeding them cantaloupe and watermelon that has been blended up, and they seem to love it. I do have one question, though. For about the past 2 weeks, it has rained nearly every day. Every morning when I go out onto the carport (this is where I have my bins) there are many worms around the top of the bin on the bottom side of the lid. At first, I thought something was wrong with the ph level or moisture level, but after checking both out on the ph and moisture meter, everything seems
to be fine. The ph was at about 6.5-7, and the moisture level was at about 80%, so I figured it couldn’t be that. After some research, I read that when rain comes into an area, it brings barometric pressure with it, and the worms, which are naturally sensitive with pressure, come to the top of the bins. Can you confirm if this is correct, and if not, could you guide me on what I am doing wrong?

Hi Chris,
Good question, but not something I can respond to with any real level of expertise unfortunately! That being said, I’ll still be happy to share my ‘2 cents worth’, and will also touch on some thoughts offered by others.

You mentioned doing some ‘research’, so perhaps you have already come across this interesting (albeit dated) thread over on the GardenWeb forum: Foul Weather Worms. Kelly Slocum, a well-respected vermicomposting expert (who sadly has moved on to other fields of endeavor), wrote a fascinating response in that thread, suggesting that low barometric pressure may indeed cause worms to roam.

The problem I see with making any sort of firm conclusions (which Slocum does not do, by the way) is that low barometric pressure also tends to go hand in hand with high moisture levels (rainfall or at least very humid air) and dark, cloudy conditions – both of which can help worms feel a little more ‘at home’ out in the open (normally bright sunlight and dry conditions will discourage this).

Similarly, in a worm bin (especially one that’s been recently set up) it is not uncommon to have worms roaming up on the inner walls and underside of the lid when it is nice and moist, and especially when it is dark. If you put the bin in a sunny (or at least brightly lit) location, most (if not all) of the worms would go back down into the bedding. Similarly, if you added a very thick layer of dry bedding at the top of the bin (something I suggest to people when they have issues with roaming worms), this will tend to dry out this upper zone, which also causes the worms to head down to where it is moist.

So, in your situation, I find myself wondering if it’s actually the darker conditions and moisture-laden air rather than the barometric pressure that’s making your worms want to roam. Perhaps a combination of both?
I personally haven’t seen any significant number of worms out on the lawn or on the sidewalk unless it is actually raining (or recently rained), even when the sky is dark and stormy weather is threatening.

Still, I feel that the notion of barometric pressure affecting worm behavior is definitely NOT off-base at all – more a matter of wondering how much is due to the pressure itself, and how much is due to the other conditions typically associated with low pressure weather fronts.

Anyway – not sure if I’ve really shed any light on this situation for you, Chris – but as promised, there is my ‘2 cents worth’!

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  1. I have wondered about this myself. I live in the area of Kansas that is the center of tornado alley. I never noticed any change in worm behavior when extreme weather happens.

    By the way, Do you know when there is a tornado WARNING in Kansas?

    You see everybody on their front porches looking up!

    • Bentley
    • September 29, 2009

    Haha – yeah, you would think it might be counter-productive for worms to be up out of the ground with a tornado blowing through!

  2. Once I started paying attention to pressure changes I came to realize that worms make great barometers.

    I think if the bin is stable the worms will never leave whatever the pressure is. I keep cardboard on top of trays of worms on my bench when getting ready for shipping orders. when the pressure is dropping most of the worms hang out on the surface under that cardboard. And when the pressure is rising they head back down.

    I’m not convinced its due to moisture as here in Nevada (Reno) it is very dry most of the time, and the worms still hang out on top.

    I hope this helps

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