Effects of Malathion on Non-Orb-Weaving Spiders

Vibration Analysis and Imaging

Irregular webs cannot be analyzed using the orb web analysis program. For these webs we developed methods to record web vibration patterns as a measure of web structural changes. The web vibrations of three species have been recorded using this methodology: Achaearanea tepidariorum, Pholcus opilionoides and Steatoda borealis. Web vibration characteristics were affected by dosing in all three species and these changes may be partly responsible for the observation that dosed spiders fail to feed (since web vibrations are used to recognize prey). We also anticipate that webs of dosed animals will not be as effective in transmitting vibrations associated with courtship and may therefore interfere with mating behavior.

A laser is reflected off the web and to a phototransistor. The output from the phototransistor is sent to a digital to analog converter (DAC) to store the data in a computer at 800 samples per second. When the web is set in motion, the vibrations are recorded and analyzed using a proprietary program.

The image to the left shows the vibration measurement instruments. The entire apparatus sits in a "sandbox" to isolate the instruments from external vibrations.

   The web vibration patterns differ among species. The image on the left is for Pholcus opilionoides  while that on the right is for Achaearanea tepidariorum. The vibration characteristics of Steatoda borealis webs were also recorded. Click to hear the web vibrations of Achaearanea tepidariorum.

Web vibrations were analyzed using a proprietary program developed in our laboratory (it is freely available. If interested, e-mail me).. The vibration characteristics were affected by dosing in all three species and these changes may be partly responsible for the observation that dosed spiders fail to feed (since web vibrations are used to recognize prey). The graph to the left depicts the change in total damping time for Pholcus opilionoides webs. We also anticipate that webs of dosed animals will not be as effective in transmitting vibrations associated with courtship and may therefore interfere with mating behavior.

. In addition to recording irregular web structure indirectly through their vibrations, we have also developed image analysis methods. For image analysis, spiders webs back-lit and imaged using the equipment shown in the figure to the left. Areas of high silk density block out more light than those of low density, allowing us to map the structure of irregular webs.

Analysis routines have been written using MathCad. Thus far, preliminary web-image data have been collected for the linyphiid, Frontinella pyramitella as well as Achaearanea tepidariorum and Pholcus opilionoides. For Frontinella, silk density increases with exposure to malathion.