In last week’s newsletter I talked about beneficial insects and how they control certain pests on farms — an illustration of how evolution works to fill ecological niches.  Ladybugs, for example, thrive on aphids.

If you’ll forgive the comparison, humans are a bit like aphids — settling into an ideal habitat, reproducing quickly, and eventually transforming it beyond recognition.  We don’t have specific predators like Ladybugs that show up when this happens.  Quite the opposite, as human civilization tends to be remarkably effective at eliminating large predators like tigers and sharks even though they don’t pose much of a risk to us.

There are plenty of species that thrive off of us, though, individually and collectively.  When parasites are discussed, we tend to imagine them as bacteria or microbes.  But animals like rats and pigeons are also parasitical in a sense, thriving off of human civilization.  And there are a host of species that achieved remarkable success by piggybacking on one of humanity’s biggest endeavors — agriculture.

Some are insects.  Thrips are a tiny insect that most humans don’t know exist — you could have a dozen of them crawling on your skin and not realize it.  And yet they are considered the most destructive agricultural pest in the world.  They damage grasses, orchard crops, and vegetables by sucking the life out of plants.  Thrips are extremely difficult to control due their high populations and rapid reproduction rates.  And they are so tiny that the wind can spread them for miles.

Powdery mildew is a fungus that evolved in concert with wild grapes and other plants.  When these plants were domesticated by humans, the mildew hitchhiked along for the ride, growing and spreading throughout the world as its host species became more and more popular.  Along the way it found other hosts, particularly squash and melons, roses, and other popular plant species popular with humans.  Because of its wide host range, it is easily spread by wind and fog.  It can be controlled by a number of chemicals, including organic ones, but is impossible to eliminate.

There are also numerous species of plants that have found a comfortable way to live off of humans, particularly in the landscapes we devote to growing our food.   Technically speaking, any plant that is growing someplace a human doesn’t want it is a weed.  But when people in agriculture talk about Weeds, they are usually talking about plants that have adapted to a very specific situation.  A good example is Palmer Amaranth, which has received attention from the national news media lately.  By developing resistance to Roundup herbicide, it has achieved tremendous success in the millions of acres of corn, cotton and soybeans where that chemical is the only method of weed control.  But Palmer is just the newest, most technophilic version of what some experts call “superweeds”.  There are dozens of weed species that have thrived in agricultural settings for centuries:  bindweed, nutsedge, purslane and many others.  Each has its own evolutionary mechanism that has allowed it outsmart humans and thrive.

Collectively, all of these insects, diseases and weeds have exerted a significant drag on humans’ ability to feed themselves.  To an individual farmer each and every one of them might appear to be as threatening as a Ladybug is to an aphid, on the whole they might actually be considered…beneficial.