Saturday, November 15, 2008

Pre-baited hobo spider traps?

hobo spider drawingWhat are "baited" spider traps?

I saw a package of "Pre-baited Hobo Spider Traps" at Home Depot the other day. Hobo spider is a species here in the northwestern US that many people are concerned about. So what are these "baited" traps all about?

First a little background. Only a few spiders ever wander very far from their webs. Most construct complicated silken webs that they use to capture prey. Because of this sedentary existence relatively few species end up indoors. Some spiders, however, spend all or part of their lives away from any sort of permanent web and wander in search of prey or mates, and thus sometimes do enter homes.

Two spiders that move readily from place to place are the brown recluse spider and male hobo spiders (drawing above). Brown recluse spiders build a simple web generally hidden away from activity. They spend daylight hours in the web but wander away at night in search of food. Hobo spiders make a more permanent funnel web where they spend most of the year. In the fall, however, male hobo spiders leave their webs and go in search of female mates. Because they are so active both spiders are commonly found in houses as well.

Bites from both of these spiders have been blamed for serious necrotic wounds. The case for venom in the bite of brown recluse spider is pretty well established, however the data are less clear in the case of hobo spiders. (See the hobo spider link above for information about what might be causing reported wounds.) Nonetheless, neither spider is a welcomed guest in most homes!

Use traps not insecticides!

In parts of the US where these spiders occur (see the links above for their distributions) the best approach to control wandering spiders is to use sticky board traps, not insecticides. Insecticides can be messy and dangerous when used indoors, and they don't work very well for these spiders. A better approach is to place sticky traps in rooms so that a wandering spider might wander in and get trapped. The traps use no insecticides. See the link below for ways to construct your own traps and how they should be placed.

So what are the "pre-baited" sticky traps baited with? I don't know. Spiders are mostly predators and respond to live prey but obviously the traps are not baited with anything alive. There is some evidence that brown recluse spider is a scavenger when live prey are scarce but these traps apparently specifically target hobo spider. My guess is that the term "pre-baited" is only marketing hype. The traps are likely just simple sticky traps similar to those you could make yourself. Bottom line: whether you make them yourself or buy them from a commercial source sticky spider traps are better than insecticides for spiders that enter homes.