Down to Earth - by Madison Co. Master Gardeners

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The "Itsy Bitsy Spider" in Our Gardens and Fields

 

May 2017

 
Humans often react to a spider much like Garfield, the cartoon cat with his rolled up newspaper:  “AAK,” splat.  As gardeners, nature stewards, and world citizens, we might do well to appreciate spiders rather than revile them.
 
Nature has a role for everything, which ultimately boils down to being an eater and being eaten.  Within that range of roles, many species, including humankind, also host other life forms in their life cycles.  Dr. Martin Nyffeler, University of Basal, Switzerland, has spent 40 years studying spiders.  He has calculated that the globe’s spider population (25 tons) annually consumes 400-800 million tons of mostly insect prey.  This equates roughly to the total human consumption of meat and fish annually!
 
So, spiders are a big deal both as insect control agents and as a food source for other predators, primarily insects and birds (13,000 species).  Despite serving these important ecological purposes, spiders generally get little respect from humans.
 
Another researcher, from Yale University, published findings which illustrate another ecological principle:  in nature, each actor (species) affects other species and is, in turn, affected by them.  In this particular study, researchers studied spider predation on grasshoppers and the resulting change produced in plant diversity within the area where spiders actively fed on grasshoppers.
 
Species diversity is one of the paramount principles around which ecological processes are organized.  Lots of diversity protects the whole ecosystem from imbalance and failure.  So, providing many strategies for maintaining diversity is nature’s way of increasing survival chances for a functioning biome (society of sustainable, interacting life forms).
 
Enter the relationship between spider species which feed on grasshoppers.  Grasshoppers, as their name implies, really enjoy eating grass.  Too much grass eating puts undue pressure on grasses in a mixed plant community.  Introducing spiders into the mixed plant community can actually influence grasshopper eating behavior.  The threat of being eaten by grassland spiders with particular hunting styles can induce grasshoppers to reduce grass consumption and increase dining on goldenrod plants. 
 
What’s the big deal, you say?  Certain common goldenrod species outcompete many other species ideally found in a functional grassland biome.  Goldenrod can form large, exclusive colonies which act to reduce the desired species diversity needed to maintain a sustainable plant community.  However, spiders feeding on grass-loving grasshoppers, and thereby causing grasshoppers to feed more on goldenrod plants, ensures that aggressive goldenrod populations are controlled enough to allow less competitive plant species (and associated life forms) to increase species diversity in that grassland.
 
So, as researchers find over and over, everything in nature is connected.  Knowing the specifics of just how that connection works can help gardeners, land stewards, and the general public work WITH nature and reduce the knee-jerk response to spray or stomp anything we consider repugnant or seen as useless.
 
The next time a spider enters your world, spend some time observing.  Their ways are wondrous.  Imagine being able to fly without wings (spinning a web strand to catch the wind and thereby disperse young spiders), or being able to weave a trap for your food from a substance you create (build webs), or being able to mimic your background color/shape so as to hide in plain sight.  The list goes on, but those are good starts.  And in the garden, observe how spiders feed on plant pests and do it for free!  Working WITH nature is central to the idea of Integrated Pest Management (IPM).

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