Wednesday, April 2, 2014

Amazing Backyard Arachnids‏

Top Left: Green Lynx female in nursery web
Bottom Left: Spiny Orb Weaver
Right: Banana Spider

One of the animal groups that people have the most difficulty in appreciating must be spiders.  Even snakes seem to have more admirers than these creepy arachnids with their eight hairy legs.  Why is this?  Could this be an innate fear from our distant past or simply something learned from our parents and peers?  Although all have a poisonous bite, few are of real danger to humans.  So I have been systematically examining the arachnids that I come into contact with to learn more about them.  They are a very common predator, indeed remarkably so if you look at the number of webs in a field on a misty morning, and this does not count the species that hunt without a web.   So here are a few examples from my backyard in Florida.

Orb weavers are a diverse group which makes spectacular webs with concentric rings of sticky silk that catch prey.  There is one particular large orb weaver which lives outside our front window and spins her web most warm evenings.  I say "her" since most spiders we encounter are the larger females; males tend to be small and inconspicuous.  This orb weaver males a new web every night and takes it down the next morning.  On this one occasion she caught a large cone headed grasshopper and is dining on its flesh which is liquified by the injection of enzymes and then sucked up by the spider.  These spiders show us how attached to one place they are since I have sometimes moved them away from a doorway and found that they return.

A very large spider that you will not ignore is the banana, golden silk spider or Nephila.  It is huge and is said to have the strongest silk of any arachnid. 

The green lynx spider is beautiful and shows a strong maternal instinct in caring for her large brood while abstaining from eating.

The Gasteracantha or spiny orb weaver is quite common and tends to end up on your face as you walk around the yard.  It's bizarre shape seems to be designed to deter predation by birds.

Top Left: Whip Scorpion with Josh Dunson.
Bottom Left: Whip Scorpion.
Right: Orb weaver eats conehead katydid

One of the spectacular spider relatives in our yard on a sandy barrier island is the impressive whip scorpion or vinegaroon, which lives in leaf litter and shallow burrows.  They are representative of migrants from western N America such as rattlesnakes, racerunner lizards and scrub jays that likely moved to FL when the sea level was much lower.  They are completely harmless to humans and only spray acetic acid when disturbed.  But they are fearsome predators of roaches and other insects and deserve protection for this reason.  They represent useful members of the ground litter community which are highly beneficial in controlling noxious insects.

So learn about your beneficial neighbors the arachnids and give them some respect.  They represent very useful members of invertebrate predatory niches which eat many troublesome insects and can be powerful friends in the management of your yard with minimal use of pesticides.   

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