True Spiders’ Characteristics Set Them Apart From Insects Nature Notes By

Patricia Martin

One of the wonderful things about Mackinac Island is that you don’t have to go far to enjoy nature. The other evening I was biking along the east shore to a friend’s house and on the way saw Common Mergansers, Black Ducks, two species of gulls, Mallards, and a Snowshoe Hare (which I haven’t seen in quite a while). On the way home I was grazed by a Little Brown Bat, and the next morning, coming down the hill from the East Bluff, I saw a Great Blue Heron on Dr. Bill’s barn, which then proceeded to fly on to the roof of his shed and stand there like a weather vane. Boy, I love this place.

You don’t even have to leave the confines of your property to enjoy the natural world. One group of organisms, which I’ve seen in abundance this year, are spiders. Every morning, fresh cobwebs have been woven in trees near the house or on the corners of the porch. Walking or riding down trails, spider webs cross the paths and can get on one’s face. Spiders seem to be everywhere, and seem to be particularly abundant this year. I really have known relatively little about these creatures, but a good friend of mine gave me a wonderful book on them called “Spiders of the North Woods” by Larry Weber.

Spider

Basically, spiders are everywhere. It is estimated that there are more than a million of them per acre. Most people know very little about these creatures and can identify even fewer. They might be able to name a tarantula, black widow, brown recluse, and a daddy longlegs (the first three we don’t have in our area and the last one is not truly a spider). I think, because of stories and movies, people have become afraid of these organisms. To quote the author of the aforementioned book, “We tend to fear that which we do not know. We tend to dislike that which we fear. We tend to hurt that which we dislike, but in the end we tend to enjoy that which we get to know.”

Spiders are in the phylum Arthropoda, which is a group of organisms which have segmented appendages and an exoskeleton (a hard outer skeleton). Included in the arthropods are crustaceans (crabs, shrimp, etc.), myripods (centipedes and millipedes), insects, and arachnids. Spiders, of course, are arachnids, a group of organisms that have eight legs. Spiders are not the only arachnids. Scorpions, mites, ticks, and harvestmen (daddy longlegs) are also in this class.

True spiders, like those we have up north here, have certain characteristics that set them apart from insects, though superficially they may be thought to resemble them. Insects have three distinct body parts, whereas spiders only have two, a fused head and thorax, called a cephalothorax, and the abdomen. Unlike insects, spiders are wingless and have eight legs (not six), and have no antennae, though spiders have another type of appendage near the head, pediplaps. Insects have a pair of compound eyes, whereas spiders usually have eight simple eyes, occasionally six.

All spiders are carnivores living on a variety of animal prey and as such are important predators, each one perhaps eating hundreds of insects in its life, unlike insects, who may be carnivores or herbivores. Insects also go through a variety of forms throughout their life cycle, whereas young spiders are basically smaller versions of the adults.

Perhaps the key characteristic of the spider is its ability to spin silk and to make webs. The word “spider” actually is a corruption of the word “spinder,” which refers to its ability to spin. Even the word “arachnid” is a spinning reference in Greek mythology. Arachnea was turned into a spider to spin and weave for eternity when she had the audacity to challenge the goddess Athena in a spinning competition.

Almost all spiders have six spinnerets, which are arranged in pairs at the posterior end of the body. Each spinneret is like a spigot on the internal glands, which produce the silk threads. The silk is a liquid in the body, but when it’s forced out and exposed to air, it solidifies into the silk threads. Spinnerets can attach to six different types of silk glands and different combinations of glands and spinnerets produce silks for seven different functions. Probably the function most commonly thought of is web creation, where both sticky and non-sticky threads are used to catch prey. Swathing prey is also done, wrapping victims for immobilization and later consumption. Creating an outer covering for the eggs requires silk. Silk is used in building retreats or shelters, either completely out of silk or by folding down leaves to form a cover. A dragline formation is the dangling thread that constantly trails behind spiders or is used to lower them from a height. Silk is also used to produce “balloons” that spiderlings (tiny, baby spiders) use to disperse with the winds.

Spider silk is very strong and has a tensile strength greater than a bone or tendon, per weight, but can also stretch, when wet, to more than three times its length before breaking. The silk produced by spiders is largely recycled material. Eighty to 90 percent of an old web shows up in a new web in a short period of time. Different types of spiders produce different types of webs, and they can be helpful in trying to identify the spider.

Spiders reproduce by eggs, which are deposited about a week after they’re fertilized. There may be one or two eggs, 20 to 30 eggs, or as many as 100 eggs deposited, depending on the species of the spider. Most spiders wrap the eggs in silk and may attach the egg sac to the edge of a web.

Since all spiders are carnivores, they all must hunt. They’re divided into two types of hunters, web hunters and active hunters. Web hunters, as their name suggests, catch their prey in a web. As the victim hits the web and gets stuck, the spider feels the vibration along the web and moves in and injects venom that subdues the prey and liquefies its insides. It may immediately kill its victim or may wrap it up in silk to save for a later snack. Active hunters may use camouflage and ambush prey or may pursue and capture their food using good eyesight and quick reflexes. Just like the web hunters, they use venom to paralyze and enzymes to break down the insides of their prey.

There are many species of spiders living in our area. From the large hairy wolf spiders to the active jumping spider, they’re quite commonly seen. They’re fairly simple to study with a hand magnifying glass, a collecting jar, and a good field guide, like the one I mentioned at the beginning of this column, and they’re very interesting.

P.S. Don’t forget to get out in the woods to see the fall mushrooms and fungi. They’re beautiful this year. Also, in response to last week’s column, it was reported that the weasel, or one like it, was seen in the Arnold Line office, checking the place out. You see, you never know when you will see “wild life” around here.

Trish Martin is a year-around resident of Mackinac Island, has earned a master’s degree in botany from Central Michigan University, and owns Bogan Lane Inn.