Last week during a walk through the woods, I ended up with spiderwebs in my hair, on my face and on my shirt. I managed to avoid a few webs because I stared into eight eyes looking back at me before I charged into the web. With those, I went around the other side of a tree to save them the trouble of rebuilding.
Spiders are like snakes and centipedes. Some will bite you, but only in self-defense.
All spiders are predators; therefore, fluctuations in population density are in part reflective of the abundance of available prey, mostly flying insects, plus an occasional lizard, snake or bird.
I recently heard from a lepidopterist friend, Peter Stangel, that "this is a big butterfly year. Our annual Fourth of July count resulted in record numbers." More butterflies can ultimately translate into more spiders, if butterflies are as careless as I was about running into sticky webs.
Fluctuations in animal numbers vary naturally from year to year in almost all species and taxonomic groups.
Abundance and rarity may alternate across years because of a variety of environmental factors, some obvious to us -- like pesticides and habitat destruction -- and others not. Lots of spiders at this time of year is a good sign, suggesting that those regional habitats are environmentally sound.
Spiders, snakes and centipedes are bellwethers of a healthy environment. The presence of numerous spiderwebs is an encouraging sign, because an alarming phenomenon is being reported in several scientific studies -- insect numbers are declining on a global scale.
This is important for spiders -- and people.
A scientific publication by Martin Nyffeler (University of Basel, Switzerland) and Dries Bonte (Ghent University, Belgium) noted that web-building spiders are declining across large regions of western Europe. One of their most common is the European garden spider, its U.S. counterpart being the large, harmless yellow-and-black garden spider most people are familiar with.
The authors state in their paper that the "dramatic population density decline" appears to reveal "a bottom-up trophic cascade in response to the widespread loss of flying insect prey in recent decades."
A trophic cascade is not to be taken lightly. Simply put, in an ecosystem a trophic level is the complex of organisms in any given tier of the food chain. The trophic level below many small animals consists of the plants they eat. Carnivores that eat herbivores depend ultimately on the plants the herbivores eat.
Destroy the plant food base and the ecosystem goes into a downward spiral. If phytoplankton disappeared from the ocean, so would the tiny krill that eat them, followed by the whales that depend on krill for a constant food supply. We often overlook the importance of small creatures at the base of a food chain.
An absence of spiders might be welcome news to an arachnophobe (which I was, until I decided not to be). The environmental message is an ominous one. We should not take lightly the disappearance of top-level predators like spiders. It may mean we have eliminated their prey.
The food web of countless animals depends on insects for food. Spiders are no exception. If they are on the decline, it probably means a lot of other, more popular animals, like butterflies, are threatened as well.
Aside from black widows, brown recluses and other species whose bites can be harmful to people, spiders are good to have around. They play a vital role in the environment.
Autumn is an ideal time to find spiders and their webs in the woods or around your yard. Instead of knocking down any webs you find, stay a while and observe. You may find it more entertaining than TV or Facebook, especially if a tiger swallowtail butterfly comes nonchalantly flitting by.
Whit Gibbons is professor of zoology and senior biologist at the University of Georgia's Savannah River Ecology Laboratory. If you have an environmental question or comment, email [email protected].