Insect Quiz March, 2005

March Quiz 2005

One evening while sitting in your favorite chair in the living room, you look up and notice a pale colored spider on the ceiling.   You recall that you have seen others like it from time to time in other rooms in your house.   You aren't afraid of the spider but you are curious about it.

1.   What kind of spider is it?

This is a yellow sac spider, Chiracanthium inclusum (family Clubionidae).   It measures no more than 1/2 inch long and is a pale yellow or cream color.   While other types of sac spiders are common outdoors, this sac spider is found very commonly inside homes.   It's active at night and usually rests during the day.   A yellow sac spider is typically found high on walls and ceilings.

2.   Is this a web-building spider?

While all spiders make silk, they don't all make webs, including the yellow sac spider. Sac spiders are a type of wandering or hunting spider, capturing their prey by actively searching and capturing them.   Yellow sac spiders do use their silk to construct tubes or retreats that they use to take shelter during the day.   This webbing is typically found in corners where the walls meets the ceiling.

3.   Is this spider dangerous to people?

While spider bites are generally uncommon, a yellow sac spider is quite capable of biting humans.   In fact, some experts suspect that this is the most common spider to bite people.   Although a yellow sac spider in typically not an aggressive spider, it will bite to defend itself, e.g. if it accidentally gets tangled up in clothes or bed sheets.   In most cases a yellow sac spider bite will cause redness and a burning feeling that lasts 30 to 60 minutes at the site of the wound.   The injured area can blister and swell but rarely becomes an open sore.

4.   What are the best ways to control this spider?

If you haven't been experiencing any problems with sac spiders, just ignore them.   If you don't want them around, use physical means to dispose of them such as crushing them with tissue paper or using a vacuum to remove them.   Look high in corners during the day for their silken retreats and remove any spiders and webbing you find.   If you experience a high number of sac spiders, try to determine what their food source is and then try to minimize it.   Without insects for food, spider numbers will decrease.   Insecticides should only be considered if you are having a hard time controlling yellow sac spiders.   Spray a residual product in areas where you see the highest number of them.   However, insecticides are only a temporary control for these spiders.