Spiders are on the move this month, but they’re looking for mates

We love spiders at the Tacoma Nature Center, and once you know more about them, we think that you will love them, too.

We talk about “spiders” as if they are one thing, but spiders are not all alike. Some are big, some are small, some spin webs to catch prey, some don’t. Some are adapted to live outdoors, others are adapted to live in buildings, caves or other protected areas. In their more than 300 million years on Earth, spiders have adapted to all kinds of habitats and conditions and thrive on every continent but Antarctica.

Let’s start with the first thing most of us think of when we think of spiders — webs. Spiders are predators, meaning they eat other animals. A typical spider in this area can eat an estimated 2,000 insects a year. Spider webs are how some species of spiders catch their food.

Webs are made of spider silks, substances that have never been re-created by science. There are seven kinds of silk that spiders can make, depending on their species and gender. Spider silk is a protein that is at least as strong as steel, so spider webs can withstand wind, rain and being hit by spider prey. Each strand of the spider web is typically made of several strands of silk layered together for strength.

To capture insects, the web needs to be more than strong — it needs to be sticky so the prey can’t get away. We’ve all seen a fly or other insect wrapped up by a spider in the middle of a web. Insects and other prey fly or fall into the middle of a sticky web that holds them until the spider can reach them, immobilize them and wrap them up. The spider doesn’t stick to the web because it knows where the sticky threads are.

The downside of having a sticky web exposed to dust, wind and other elements is that it gets ruined in a hurry, so sticky strands of spider webs typically last only one day. Spiders have to do continual repair to their webs. Some spiders have to make a brand new web each day They will eat their web so they don’t waste that protein, rest up a little and then get started on the day’s new web. Spiders were very early adaptors of the concept of recycling materials.

As much as we humans think of spiders as having webs, not all spider species spin webs to catch prey. Some species are passive hunters, building silk-lined funnels and waiting for prey to wander in. Others are active predators that hunt their prey just like a lion. There are also ambush hunters that take cover and pounce on prey that comes close. There is truly a spider for every niche.

There are around 3,000 species of spiders in North America. We don’t have that many locally, but we do have a wide variety of spiders here — indoors and outdoors. Did you know the spiders you see outside are usually totally different species than the spiders you find indoors and under buildings. The spiders that associate with buildings are generally not adapted to be outside. They live their entire lives indoors, largely unseen by humans.

Spiders are especially obvious to humans this time of year. That is not because there are suddenly more of them. This is the mating season for most species — they need to mate and lay eggs before the winter comes. Many spiders we see in the fall are males on the move looking for females. Males have to wander in search of more secretive and sedentary females to mate with in lots of spider species.

This story was originally published October 8, 2016 at 6:18 AM with the headline "Spiders are on the move this month, but they’re looking for mates."