Effects of Malathion on Orb-Weaving Spiders

Low doses of stimulants, depressants, hallucinogens, and other pharmaceuticals are known to affect the nervous system and web-building behavior of spiders (Witt & Reed 1965; Witt, Reed, & Peakall 1968). Likewise, low doses of pesticides have also been shown to affect web-building behavior. Recent research by a European team has demonstrated that orb webs are efficient collectors of agrochemical sprays (Samu, Mathhews, Lake & Vollrath 1992). In addition, this group showed that web building by the araneid spider, Araneus diadematus is affected by Fastae (a pyrethroid insecticide), resulting in decreased web size, building accuracy and web-building frequency (Samu & Vollrath 1992). The effect of sublethal doses of malathion on orb weaving behavior was explored in our laboratory for four spider species: Araneus diadematus, Araneus cornutus, Araneus trifasciata, Araneus marmoreus, and Argiope argentata. Data are presented here only for adult female A. diadematus.

Spiders were collected from pesticide-free sites and reared in 100 X 100 X 10 cm cages under natural photoperiod. Web images were recorded daily for one week prior to dosing using a video camera and digitizing board to generate baseline data (animals served as their own controls). Spiders were then exposed to 10 ul of 10^-4 or 10^-7 malathion for 24 hours and returned to their cages. Following dosing, webs were imaged daily. The digitized webs were analyzed to record features related to web size and regularity using a proprietary computer program written in our laboratory. These data were analyzed to determine trends related to dosage and to look for possible recovery. Orb web construction by A. diadematus was adversely affected by malathion with dosed animals building significantly smaller webs with greater irregularity. In addition, spiders showed no evidence of recovering from the pesticide over periods of up to 33 days for 10 ^-4 dosed spiders and 58 days for 10^-7 dosed spiders (spiders at higher dosages survived for a shorter period than those at the lower dose). Orb-weaving spiders provide an unique opportunity to record long-term changes in the behavioral state of the spiders since data can be easily collected through photographic techniques and later analyzed at our convenience.

Copies of the Web data collection routines and data analysis routines are free and available for Windows 3.1 or better systems. You may request copies by E-mailing me (btietjen@bellarmine.edu)

Adult female Araneus diadematus were collected from pesticide-free sites and exposed to 10 ul of 10^-4 ("high dose") or 10^-7 ("low dose") malathion for 24 hours.

Spiders build webs in 1.0 X 1.0 X 0.1 meter cages. By lighting the cages from the side, spider webs can be video taped and later digitized into a computer using a frame grabber. Webs were imaged daily (for up to 58 days post-exposure), video taped, digitized, and enhanced for later analysis.

  Web structures are identified by mouse clicks on the computer image. This results in a vectorized image to be analyzed by a proprietary computer program.

The program extracts statistics from the image including web catch area, a web regularity index, mesh distances, radii angles and lengths. A second proprietary program extracts the web measurements and generates summary statistics for each web. These data can be transferred by the clipboard to our statistics package (Stata) or a spreadsheet.

Some animals only built irregular smears that could not be analyzed by the analysis program. These webs are excluded from the following discussion.

   Dosed spiders typically built webs that were smaller and more irregular than undosed animals. The images shown are displayed at the same scale and are from the same spider (before and after dosing with 10 ul of 10^-7 malathion for 24 hours. Spiders were monitored for 33 days (high dosage) for up to 58 days. None recovered and built normal-sized, regular webs.

   Argiope trifasciata results.

  Spiders on Drugs