I have to admit that when I relocated to Washington a long time ago, I was deathly afraid of spiders. Since then I have come to appreciate these much misunderstood beneficial arachnids.
Spiders are not insects. They have two body segments, eight legs and eight eyes. They also have a pair of chelicerae, appendages resembling fangs but serving as jaws. In addition, they have a pair of pedipalps, appendages resembling small legs that are used for sensing objects, for helping construct a web, and for holding onto prey. Unlike most insects, spiders do not have antennae or wings, but they are capable of producing silk their entire life.
What makes spiders beneficial is that they prey on insects, providing us with natural pest control. What makes them scary is their appearance and the fact that almost every type of spider is venomous. However, that does not mean they are harmful to us. Generally, most spiders do not possess venom that causes humans any injury. If their venom does cause a problem, it usually is just an itchy bite. Out of the approximately 50,000 species of spiders that exist in the world, only about 25 of them are capable of causing human illness, and none is considered deadly.
The reason spiders possess venom is to aid them in gaining control over their prey who no doubt try to escape when captured. Spiders are not intent on attacking us and “taking us down” as prey. The most venomous spider in the U.S. is the black widow, and it only bites humans when disturbed or threatened.
Spiders take different approaches in capturing their prey, which are usually insects. Some build sticky webs and wait for an unsuspecting insect, such as a fly, to become stuck in the strands. As the insect struggles, the spider injects it with venom to immobilize or kill it. Other spiders build webs with dry silk and quickly attack their prey when the vibrating strands alert them of their dinner’s presence. About half of all spider species do not spin webs for capturing prey. Some spiders hunt down their victims, while others sit in hiding to wait for dinner to pass in front of them.
As fall approaches, many homeowners fearful of spiders migrating indoors from outside will spray their yard and home foundation with pesticide to kill the spiders. This is shameful. Spiders are our friends, eating all sorts of other insects and providing natural pest control, just like preying mantids, lady beetles and other beneficial insects.
This spraying is also misguided because most of the spiders found living inside a home are house spiders, not outdoor spiders. House spiders are ones adapted to indoor conditions that are not favorable to outdoor spiders. House spiders arrive in homes as egg sacs with building materials used to construct the home or on household goods. They spend their lives hidden somewhere within or under the home. When you see them in the early fall roaming about the house, they are in search of females for the purposes of mating.
Outdoor spiders are not well adapted to the limited food and water supply available inside a house. They will stay outdoors, not migrate inside to find a cozy place for winter. They are adapted to surviving winter outdoors. If they get lost and come indoors, they will die.
If you do have a number of house spiders start appearing in your house in the fall, they have come from somewhere within the house. While creepy, it should not cause you sleepless nights. Just buy a bunch of sticky spider traps at the hardware or grocery store and place them along baseboards in the corner of rooms or under the beds. If cobwebs are a problem on the outside of your house or on shrubs, simply brush them off with a broom or use a forceful spray of water to wash them off. Remember, spiders are our friends.
Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.