Spiders In and Around HomesBy: Michael Waldvogel and Charles Apperson, Extension Entomology
|Insect Note - ENT/rsc-1|
Spiders have a well-established but largely undeserved reputation as being dangerous to the health of people and their pets. In truth, spiders are extremely beneficial because they prey on many insects that we consider to be true pests in our homes and gardens. Not all spiders build elaborate webs to catch their prey. Some species ambush their prey from tubular tunnels built in the ground, under rocks or other areas. Other species simply build a loose collection of webbing in which they live. These types of spiders, such as the wolf spider shown here, are the ones that most frequently invade homes. They may remain hidden for most of the day, then hunt for prey at night.
Spiders are not insects. They are close relatives of ticks, mites and scorpions, which all belong in the group called arachnids. Unlike insects, which have three main body sections and six legs, spiders have two body sections and eight legs. The eyes, mouthparts and legs are found on the front section of the body, known as the cephalothorax. The second section, the abdomen, bears the parts of the respiratory system (spiracles and/or book lungs depending on the type of spider), the digestive and reproductive systems, and the external organs used for spinning silk or webbing. Most spiders are identified by size, color, markings on the body and the number (usually six or eight) and arrangement of eyes. Female spiders wrap their eggs in a silken spun sac. Some spiders carry this egg sac, while others deposit it somewhere within their nest. Hatchling spiders (spiderlings) often produce a silk thread that allows them to disperse by "ballooning", i.e., being blown by wind currents to other areas.
Encounters between people and spiders are usually accidental and bites are a response by the spider when its web or nest is disturbed. Most spiders produce venom therefore, they could be considered "poisonous". The venom is stored in glands that empty into the spider's fangs or chelicerae. For the most part, spider bites are insignificant. However, just as bee and wasp stings may trigger allergic reactions in some people, the same can be true for spider bites. Young children, the elderly and hypersensitive individuals are more likely to react more strongly to a spider bite. In North Carolina, there are few spiders that can inflect serious and painful injury. The two best-known poisonous spiders found here are the black widow spider and the brown recluse.
Spiders are beneficial and control
many insects that feed on the flowers, shrubs and other plants in our gardens
and natural areas. Spraying for spiders in these areas may actually
increase the number of pests by killing off other natural enemies as well.
Web-building spiders are most likely to show up in areas where insects are
abundant, e.g., wood piles, around porch lights, windows or water sources
(such as water spigots). Knocking down these webs with a broom or burst
of water from a garden hose is adequate for "control". Outdoor pesticide
applications for spiders are largely unnecessary and should be avoided.
On occasion, you will find spiders on objects or in areas that have been
left undisturbed; this can include sandboxes or even children's toys. Check
these items periodically for signs of spiders. Spraying pesticides around
sandboxes or other play areas should be avoided whenever possible.
Finding a large number of spiders indoors usually means that there is an ample supply of insects and other "spider food" in the area. Any real attempts to get rid of spiders should focus on eliminating these insects. The long term solution includes non-chemical measures:
There are a number of short-term
solutions to spider infestations, as well. Knocking down and removing
webbing, or mechanically removing/killing the spiders should be sufficient.
Vacuum the areas along baseboards, in corners and under and behind furniture. Clean
bookshelves periodically. If you're concerned that more spiders will show
up (or hatch from an unseen egg sac), then you could resort to applying
an insecticide along baseboards, in corners, and inside storage closets.
Select a pesticide that is labeled for use against spiders indoors. Always
read the insecticide label for complete instructions on how and where
to use the product. Crawlspace are often attractive environments for spiders (but not necessarily the source of spiders entering your living area). Treating your crawlspace is an option, but simply setting off foggers ("bug bombs") is not likely to be effective and can be hazardous particularly if you contaminate your heating/AC ventilation system. Crawlspace treatments, if needed, are
often best left to pest control professionals. The availability of particular
insecticides may change from year to year, so consult the latest edition
NC Agricultural Chemicals Manual
or your local county Cooperative
Extension office for advice on selecting insecticides.
Tips on Avoiding Spider Bites
Follow these suggestions to reduce the chances of being bitten: