Spiders in the Forest
By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester
Some of the smallest, but most important predators at Tryon Creek State Natural Area (TCSNA) are our spiders. Spiders are the most voracious predators in the world, consuming far more prey than larger, more dramatic predators like owls and coyotes. It was estimated by an eminent spider scientist that the all world’s spiders together each year consume a weight of insects greater than the weight of the human population of England.1
Spiders: Voracious Predators
Spiders catch their prey in variety of ways, the most obvious being those that weave webs. Just a brief look around TCSNA reveals that we are home to many different kinds of spiders and their webs.
The Orb Weavers
The most common and recognizable group of spiders are the orb-weaving spiders, named for the shape of their webs as seen below. These webs are designed to help the spider catch flying insects for food.
After weaving the orb web, the spider will most often wait upside down in the center of the web for some hapless insect to become stuck to, and entangled in, the web. The thrashing motion of the insect trying to escape attracts the spider’s attention. I have also observed a situation where a Douglas-fir needle fell into a web and got stuck. The spider ran down and disentangled the needle and threw it down. Unfortunately it got tangled again lower in the web. The spider went down further, and repeated the process, this time the needle fell free of the web. The spider then returned to the center of the cleaned up web to continue monitoring the action.
Once the victim is in the web, the spider will rush to the insect and inject it with poison to kill it. Sometimes, as seen below, the spider will wrap up the insect for future use.
The Mat Weavers
A slightly less common type of spider is the “mat weaving” spider. I was lucky enough to be in the park on a dewy February morning which highlighted one of the better examples of a “mat” web that I have ever seen. It is a flat web suspended by strands from the overhanging branches. This particular web measured about 3 inches across. Typically, these mat webs are not sticky, and the spider is lurking very near and when an insect gets into the web, the spider rushes over and poisons it before it can escape. These kinds of webs can also be found in the crevices of large tree trunks.
The Funnel Weavers
An even less common type of web is made by “funnel weaving” spiders. The example below was found along the Middle Creek Trail. While it may not be obvious in the photo, this really is a three dimensional funnel. The spider typically waits near the bottom of the funnel.
The Dome Weavers
A fourth kind of web which you may occasionally encounter at TCSNA is the product of a dome-weaving spider. Again, these webs are not inherently “sticky” and the spider will rush towards the insect which is trying to escape the web and inject poison into it. The example shown below was near the Iron Mountain Trail, and was approximately 1 foot wide.
While it is the large spiders and their webs that attract our attention, the population of “tiny” spiders is considerable. Worldwide, more than half of all spider species are less than 2/10 of an inch long1. The spider below was living in a shrub with no obvious spider web. It is important to know that a significant number of spider species do not use webs to catch their prey. This spider MAY be among them.
Shy and Sexy Spiders
Spiders reproduce from eggs. Spiders’ sexual encounters are frequently a one-time event for the males, not because of any spider-y sense of monogamy, but because the female will oftentimes eat the male immediately after mating.
In some species the female will create a protected place to lay her eggs. Examples of this behavior can be seen by looking for folded leaves. When you consider that one small spider was able to fold over this leaf and fasten it together, it is nothing short of amazing. An example found along the Old Main Trail at TCSNA is shown below.
The underside of this folded leaf is shown below. The white areas between the leaf edges are web strands which hold the structure in place. I was able to see an adult spider inside of this “nest” but my attempts to get a good photo of her were not successful.
A less dramatic, but still interesting example is shown below in which the mom spider just rolled up part of the leaf to create her nest. She is still on guard. The empty “skin” just to her left might either be the remnants of her nutritious sex partner, a recent meal or her own recently shed exoskeleton. Just for scale, the brown thing she is standing on is a Douglas-fir needle.
Gently unfolding this leaf just a bit revealed part of her nest, and also excited a few of the newly hatched young spiders into action. The young spiders, one of which is highlighted with the red arrow in the photo below, started scurrying around as I unfolded the leaf, but none of them went very far. After I looked, the leaf rolled up again quite nicely.
The young spiders were almost unimaginably tiny. They were way outside the range of what my camera was designed to photograph. Some species of spiders are reported to eat plant material when they are young, and graduate to insect food as they mature.
Yeah for Spiders!
The spiders of TCSNA are a tremendous aid in controlling insect populations that could devour tons of plants and be much more annoying to our human visitors. While they are a lot less visible and dramatic than other predators at the park, they are likely much more important, at least in the amount of insects they consume. Next time you’re at the Park, pause for just a moment at a spider web, and thank the spider for all it does.
1Dalton, Stephen. Spiders: The Ultimate Predators. Firefly Books Ltd. 2008