Life Beyond Halloween: How the American Grass Spider finds Optimal Web Locations on Our Campus

It’s almost Halloween, the time of year when fear seems to be the most popular emotion to express amongst your friends and family. It’s the time when every creepy-crawly apparition from our nightmares appear as decorations everywhere. As one of the creepiest and crawliest, the spider takes center stage. Outside of bad 1950’s horror films and haunted house decorations, how do these nonfictional monsters interact with one another and survive as a community in our everyday lives? A study done by S.E. Riechert (1976) demonstrated that the funnel web grass spider Agelenopsis aperta actively seeks out places to spin their webs based on specific features of their environment. 40 years later, this study’s findings still provide great insight on what defines web locations within a spider community. Furthermore, it can be used to address how these Halloween celebrities orient themselves when faced with environmental stresses such as urbanization. We sought to expand upon this foundational study by looking at web distribution and species abundance within a microhabitat of undisturbed shrubs within Grinnell College’s campus. 

           

 In both desert grassland and lava beds in New Mexico, S.E. Riechert (1976) illustrated Agelenopsis aperta’s active selection of web sites in response to environment suitability. Within the study, a total of 222 Agelenopsis aperta were captured and marked in order to quantify movements between web sites. Scores were given to each of the environmental variables measured, such as leaf litter or nearby plant species, which ranked each variable based on how useful it was for the spider to pick a good web site. For both desert grassland and lava beds, the presence of litter and various plant species were found to be the most influential factors in selecting suitable web sites. Litter provides shade and a more optimal thermal environment for the spiders, whereas the presence of certain plant species increases the insect (for the spider, more insects mean prey) density of the site. Because Agelenopsis aperta is a “sit-and-wait” predator that utilizes non-sticky sheet webs, keeping cool in the shade as well as increasing the chances of prey landing on its web are both crucial factors in determining suitable web sites. However, more studies need to be done in order to understand the underlying mechanisms of active web site selection within a microhabitat.

Although the study conducted by Riechert (1976) adequately addressed the environmental characteristics that define web site selection, spider interactions with one another seemed to be placed on the back burner. The territoriality of these spiders could add to the reasons behind their distribution. What if site suitability is relatively equal throughout the entire microhabitat? Do intra-species interactions then dictate web dispersion? We sought to answer these questions by looking at the abundance and web distributions of the American grass spider Agelenopsis spp. within a relatively undisturbed region of shrubbery on Grinnell College’s campus. We are investigating web characteristics such as surface area, height from ground, and distance away from its nearest neighboring web that will lead to a better understanding of how these spiders coexist in a microhabitat with lots of litter and insects to pick from. Learning how and why spiders arrange themselves under these conditions could lead to improved methods of species conservation, ensuring that spiders will be around for many Halloweens to come.

Riechert, S. E. "Web-site selection in the desert spider Agelenopsis aperta."Oikos (1976): 311-315.