Spiders are practically everywhere. They live on nearly every continent and are part of every common ecosystem imaginable. Spiders may look small and insignificant -- OK, and kinda creepy -- but they're important predators and prey for a multitude of other animals. As any horticulturalist can tell you, they're great garden allies, too.
Here, There, Everywhere
Spiders are endemic to every continent except Antarctica. Some species are terrestrial, that is they live on the ground, while others are arboreal, meaning they live in trees. Beyond this distinction, they've also displayed a penchant for living in far-flung climates and habitats, from tropical forests to ice-cold caves. Some specialist species live in a combination of extreme conditions. Case in point, the Kauai cave spider, who lives in lava-tube habitats in Hawaii. While some spiders are social, most are solitary and interact with each other only to fight or mate.
Spiders eat lots of insects, mostly those smaller than themselves. Taken as a whole and given the diversity of species assemblages in most ecosystems, spiders' primary niche in nearly every ecosystem is controlling insect populations. Some families, like orb weavers, do this through passive hunting with their signature webs. Others, like wolf spiders, do this through active hunting. Because many species overwinter, they can help reduce prey numbers early in the agricultural season, giving farmers, horticulturalists and gardeners a leg up on the season, according to Colorado State University. Spiders also kill other arachnids and spiders -- even those of the same species -- which helps keep their own numbers in check. Furthermore, spiders are an important food source for a variety of birds, lizards, wasps, and, especially in deserts, mammals.
Most spider species are generalists and have long generation times in comparison to prey, ergo there are no natural control species of spiders per se, according to the University of Michigan. This means introducing a given type of spider to an area -- or removing it -- can have little to no effect on most ecosystems. Indeed, studies synthesized and summarized by University of Maine researchers in 2003 show multiple spider species are more effective at reducing insect populations than single species. As such, it's hard to pinpoint a precise niche for a precise spider. They're no go, for instance, in stopping the singular, explosive outbreak of a single pest species. Still, spiders are far from superfluous to a given ecosystem when considered as a whole. If anything, new, different spider species are important for the simple fact that they're different from those already there.
Spiders introduced to humans in natural or artificial ecosystems, integrated or not, likewise have good and bad impacts. On the positive side, chemicals harvested from spider venom help control and treat several diseases. Likewise, spider silk, which has proved to be the strongest natural material, has inspired mechanical engineering to new heights. On the negative side, spider are blamed for numerous bites, some of which have been deadly. All spiders have venom, but, in fact, most of the dangerous ones shy away from people. Moreover, their bites aren't deadly to healthy adults; they're just painful and really uncomfortable.
- University of Arizona Center for Insect Science Education Outreach: Spider Information
- Skerl, Kevin L.: Spider Conservation in the United States
- University of Main: Spider Predation in Agroecosystems -- Can Spiders Effectively Control Pest Populations?
- Rayor, Dr. Linda S.: All About Spiders
- Environmental Entomology: Arboreal Spiders in Eastern Hemlock
- Ekológia: The Spieces Composition, Whitin-Plant Distribution, and Possible Predatory Role of Spiders (Araneae) in a Vineyard in Southern Portugal
- Rice University: Snakes Minus Birds Equals More Spiders for Guam
- Community and Ecosystem Ecology: Niches Among Four Species of Orb-Weaving Spiders in a Grassland Habitat
- Journal of Arachnology: Day Versus Night Sampling for Spiders in Grape Vineyards
- University of Wisconsin: Ecological Adaptation Likely to Influence Impacts of Climate Change