If you've ever tried to catch a parson spider, you know how frustratingly fast they are. Part of that's because of their hunting habits, but part of that's because of basic spider biology and locomotion.
Although it's hard to identify most species of spiders, the eastern parson spider, Herpyllus ecclesiasticus, is an exception. Although they take up less space than a quarter and share their brown and gray coloring with many spiders, parson spiders have a distinctive, practically unique body pattern: a white striping akin to the clergy cloth once worn by parsons. You can find them inside and outside from the central United States to southern Canada. They're common house pests, though hardly poisonous, and they're notoriously fast movers.
Like arachnids and unlike insects, all spiders -- including parsons -- have four sets of legs. They walk by alternating two pairs of at a time, which affords them impressive stability and the ability to change direction quickly. Perhaps the most unusual facet of their locomotion is their combination of hydraulics and muscles. As a spider's blood circulates, its legs extend from hydrostatic pressure, the rate of which is tied to its heartbeat. Then it uses its muscles to flex the legs back under it. Although most spiders maintain relatively low hydrostatic pressure, they can willfully increase it up to eight times their resting pressure when they're running or jumping, according to Cornell University.
Parson spiders don't spin traditional webs -- they depend on their speed to capture their prey and avoid predators. Because they hunt at night, they're generally fastest then and slower during the day. When they're resting, they generally hide in silk nests in nooks in crannies, inside or outside. Although the top speed of parson spiders isn't readily discernible, they can move many times their body length every second. Still, they're slower than spiders in the Araneae family, which includes the giant house spider (Tegenaria duellica), which holds the record of fastest true spider at 1.7 feet per second.
Like most of their New World brethren, parson spiders have both a trachea and book lungs, the latter of which is their primary means of breathing. As with their legs and movement, a spider's book lungs are dependent on hydrostatic pressure. When a spider's heart rate and hydrostatic pressure increase, it's harder for it to breathe, but it can move much faster, at least for a short period. That's why spiders are sprinters, not marathon runners. If you're encountering a parson spider, though, it's likely in your home, and a spider-accessible hidey-hole probably isn't too far away. Pair the parson spider's bursting speed with its ability to scale walls and, in some instances, jump, and you've got yourself one agile spider.
- Cornell University Insect Diagnostic Laboratory
- University of Nebraska-Lincoln: Spiders of Medical Importance
- University of Wisconsin: Common Spiders In and Around Homes
- National Geographic: Spider Sense -- Fast Facts on Extreme Arachnids
- Burke Museum: Myths, Misconceptions and Superstitions About Spiders