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San Diego Floral Association
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Friend or Foe: Spiders
Reprinted from: November/December 2009, Volume 100, Number 6
Most people fear spiders and while spiders may look scary, most are incapable of harming people and actually are extremely beneficial to your garden.
The majority of spiders only bite humans in self-defense and even then, the bites are barely worse than a mosquito bite. The most fearsome of spiders, the recluse spiders (Laxosceles) or widow spiders (Latrodectus), will only bite when they feel endangered themselves. (Currently, brown recluse spiders do not reside in California.)
Spiders have many benefits to humans. For example, cooked tarantula spiders are a delicacy in Cambodia. Spider venom is being tested for possible medical uses such as the treatment of cardiac arrhythmia, strokes and even Alzheimer’s disease. Spider silk is even being considered for use in clothing.
The place where spiders are most beneficial, however, may be your garden. Spiders are terrestrial predators and eat tons of pest insects every year but do not eat plants. This makes them one of the best biological control agents for gardens.
Spiders can be found in almost any environment and will eat more or less anything in large amounts. Dr. Linda S. Rayor of Cornell University adds, “Since many spiders overwinter as adults, they can reduce prey numbers early in the season before other biocontrol agents are active.”
To increase these benefits, try increasing the number of spiders in your garden by using mulch, providing places for homes such as crates, growing tall plants and flowers that bring prey and being careful when spraying pesticide.
Before you consider having only spiders for biological control, know that there are disadvantages to having them do all the work. Spiders are generalist predators and while they will eat pests, they also will also eat non-pest insects and other beneficial predators.
If you do find that you need to manage the spiders in and around your home and garden, remember that first and foremost spiders are beneficial and pesticide control is rarely necessary. Removing hiding spots and regularly cleaning webs off the house is the best technique for spider control.
The bottom line is that spiders are definitely a friend and not a foe. —Alyssa Holderbein
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