How Spider Webs Can Detect Air Pollution
Classic spiral spider webs are made by orb-weaving spiders which weave them deadly traps for flying insects. But orb spider webs are also electrostatically charged, making them perfect for capturing not only prey but pollen and other small pollutants, indicators of an environment's health.
The webs are made of long strands of intertwined silk, and the compounds in the silk attract water molecules that will coat the entire web. It is this water that establishes a charge. The web then attracts any charged objects that come close to it. Many insects pick up a charge by flying through the air, just as your body becomes charged when you shuffle across the carpet in your socks. So when an insect flies near a spider web, the stretchy, flexible silk strands will actually bend towards the insect and catch it. Depending on the size and charge of the prey, the web can move up to two millimeters toward it. Two millimeters is a huge distance compared to the thickness of the silk, which, on average, is ten times smaller.
The electrostatically-charged webs also catch pollen and small pollutants in the air. Just as insects do, particles in the air collect a charge as they move. And, just as they capture insects, the orb spider webs capture these minute particles. Large amounts of these particles, which include harmful aerosols and heavy metals from vehicle exhaust pipes, can be detrimental to spiders, as they often ingest old or damaged webs before constructing new ones, including any substances caught in the web.
Some current studies are analyzing the chemicals and pollutants caught in spider webs to determine the health of certain environments. The results show some of the impacts humans are having on nature. One study collected webs based on their proximity to roads and busy highways and determined the amount of minute heavy metals caught on the silk. Another study is collecting spider webs from homes to analyze the health of our living environments.
"Field Notes" is produced by the Montana Natural History Center.