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 webs to snare their prey. Some species ambush their prey from tubular tunnels built in the ground or under rocks. Other species simply build a loose collection of webbing in which they live. These types of spiders, are the ones that most frequently invade homes. They may remain hidden for most of the day, then hunt for prey at night.
Biology of spiders
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 spiracles (openings for breathing), 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.
How dangerous are spiders?
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 Brisbane, there are few spiders that can inflect serious and painful injury is extremely small. The two best-known poisonous spiders found here are the redback spider and the trapdoor.
Control of Spiders Outdoors
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.
Control of Spiders Indoors
Finding 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:
Sanitation - reducing or eliminating conditions that attract insects, e.g., high moisture and ready access to food of some sort.
Find the entry points used by both insects and spiders and seal or close these areas.
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 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. Treating your crawlspace is an option, but exercise extreme caution when applying pesticides in such confined areas without adequate ventilation and personal protection. Crawlspace treatments are often best left to pest control professionals. The availability of particular insecticides may change from year to year. If in doubt consult a professional
Tips on Avoiding Spider Bites
Follow these suggestions to reduce the chances of being bitten:
Always check for spiders before sticking your bare hand(s) into dark corners or areas.
Always wear work gloves when handling boxes, firewood, lumber and other items that have been stored/stacked undisturbed for some time.
Vigously shake clothing and shoes that have been left undisturbed for some time to dislodge any spiders and inspected before wearing.
If you think you have been bitten by either a redback spider or trapdoor, carefully apply ice or a cold-pack to the bite and seek medical assistance. If you can catch the culprit spider, bring it along for positive identification.