A spider sits in the center of its web, awaiting lunch. Photo: Terry Jellerson
By Kevin McKeon, Maine Master Naturalist
Spider-like marine creatures crawled onto land about 400 million years ago, and about 25 million years later evolved spinnerets — organs to produce silken thread. There are estimated to be well over 100,000 species of spiders on Earth. In 2020, after a 14-year effort led by Dr. Daniel Jennings and aided by entomologist Charlene Donahue and the Maine Forest Service and Department of Inland Fisheries and Wildlife, “A Checklist of Maine Spiders” was published. This herculean effort is available online. Of the 677 species that they’ve cataloged, none are considered dangerous to us, although some highly sensitive folks may have a reaction to a bite from an otherwise harmless spider. On rare occasions, black widow and brown recluse spiders are found hidden in produce transported into the state, but our cold winters prevent their establishment.
Maine’s largest spider is the fishing or dock spider, Dolomedes triton. At over 4 inches long, these crawlers can seem quite intimidating, but their bite is like a mild bee sting. They scamper on and dive into water, staying submerged for up to 90 minutes while breathing from captured air bubbles, eating insects, tadpoles, and small fish. They’re also found in wooded and housing areas.
Speaking of insects: Spiders aren’t insects. They are grouped with the scorpions, ticks, and mites as arachnids, which all have eight legs, no wings, and no antennae; insects have six legs, and three body segments instead of the spiders’ two. Insects also have compound eyes; spiders usually have about eight simple eyes.
When we think of spiders, webs always come to mind.
Spiders use their silk for many things: Wrapping their eggs, building shelters, traveling throughout their habitat, flying to new habitats (“kiting”), capturing prey, storing food (wrapping their prey), creating “guylines” during travels that assist in returning to their nest. Silk can also serve as anchors to break both unexpected falls and escaping predators, “trip lines” to alert of prey, and of course building their webs. Some silk is even impregnated with pheromones to attract a mate.
One of nature’s many marvels, a spider’s main structural silk — the dragline — is about 15 times thinner than a human hair, and it’s made up of even smaller nanostrands measured in billionths of a meter. Some strands are five times stronger than steel, some are seven times tougher than Kevlar, and others are able to stretch 30 times their original length.
All these uses require different types of silk with specific properties: Sticky, strong, elastic, light, scented, or even impregnated with sperm. Silks are made from spidroin proteins, the same protein group as collagen and keratin, and stored as dope in various glands. It becomes silk as the dope is pulled from the gland, a process called pulltrusion (“pull” + “extrusion”) — the same manufacturing process we use for glass and carbon fibers. As the dope is pulled, the spider’s spinnerets — as many as eight of them — form it into silk using pulltrusion speed, tension, thickness, and pressure as needed, to form the desired silk type. Air exposure and pressure act to immediately dry the silk.
So, here’s our spider sitting in the middle of its web with its eight legs spread out and affixed to webbing strands. Our spider’s body is covered with thousands of “slit sensilla” — sensory cracks specialized to sense vibrations, with concentrations at the spider’s leg joints. These exquisitely sensitive sensilla alert our spider to anything entering its web. So fine-tuned are its sensilla that differences among twigs, leaves, wind, and size can be ascertained, and proper responses made; leg positioning on its web identifies the location within the web of this disturbance. So if it’s a twig, our spider does nothing; but if it’s a fly, off it goes to either eat it or wrap it up for storage. Thus, our spider’s web becomes an extension of its sensory world.
Now, along comes a smaller spider and sees our guy’s large web. Smaller Guy will very gently attach his own silk thread to our guy’s web, then sit back, hidden, and wait. If Big Guy decides to wrap and store its prey, Smaller Guy will feel it on his thread and very gently creep along its thread to the stash and ever so gently eat it…like a mosquito crawling along us looking for a blood-meal. Some assassin bugs specialize in spider capture and can creep with such stealth as to attack our spider as it sits on its web. Jumping spiders will mimic struggling, web-caught prey to lure our guy into an ambush. So, getting caught in its own web can be a fact of life for a spider.
Webs can be “adjusted” to better perform. Web threads are originally woven to differentiate among different speed and strength vibrations; this allows our spider to determine the distance to, and size of its captured prey. Threads are added to increase or decrease web tension to better suit environmental conditions like early morning dampness vs. mid-day dryness, temperatures, even varying conditions of the web’s attachment points. More threads are added to existing webs to both increase sensitivity and allow smaller prey capture.
Web sensitivity can also be adjusted by the spider positioning itself in either a spread-out posture or a crouching stance, effectively compressing or stretching its slit sensilla, thereby adjusting its vibrational acuity — something akin to our squinting for a better look. This also better informs our guy of the size of prey; if it’s not so hungry, smaller prey can be ignored.
Spiders are just about everywhere: at least 10,000 per acre of woodland, and up to 2.5 million in an acre of field. Even in our homes, we are rarely 10 feet away from a spider; it feeds on things that feed on us, like mosquitoes and bedbugs. So maybe consider moving one of these wayward friends from your sink or floor to a potted plant, and keep that web in your room’s corner active a bit longer — give it a life of keeping house pests at bay.
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