Well, not quite bugs – microbes!  As someone who still squeals every time I see a new type of soil organism beneath the microscope, imagine my delight to discover that these same microbes are an important catalyst for the formation of rain, hail, and snow, and are thought to be responsible for up to 80% of local precipitation.

It’s called bioprecipitation, and here’s how it works.  Water vapour and microbes (mostly bacteria and fungal spores, but also many other organisms) are released from the soil and plants as aerosols, travelling up into the sky.  Falling rain on the surfaces is one way this happens.  Once up in the atmosphere, water molecules need a point – an ice-forming  nuclei – on which to crystalise around before falling back to the earth.  We used to think mineral and dust particles were the catalysts, but now we know that most precipitation formed at atmospheric temperatures between -7 and almost 0 degrees celcius is actually crystalising around living biology.  How cool is that?

This has obvious benefits to the microbes for dispersal (for example, plant fungal pathogens in the Puccinia genus, also known as rusts, spread this way).  But what is really neat is to consider the broader biofeedback cycle thought to be at play here.  Plants and soil microbes need moisture to thrive, and they have the ability to create their own rain and strongly influence regional water cycles.  The reverse is also true – degrade the soil or remove the plant cover, and there will be a loss of water vapour from vegetation and a loss of microbes for forming rain.  

We are only beginning to understand how agricultural practices are affecting regional water cycles.  And yet we have a long record of human agriculture and changing landscapes – think of historical breadbaskets and homes to ancient civilisations that are now arid and desertified.  To delve into the agricultural history of soils in geological time, a great resource is “Dirt:  The Erosion of Civilisations” by David Montgomery.  Read it slowly, with tea in hand, and be prepared to be shocked into doing something about it.