A wolf spider seen last month in a Unity park. Photo by Dana Wilde

At the end of March after the snow was gone, I was mindlessly poking around in last year’s grass at the park, when what to my wondering eyes should appear but tiny black glints of activity. I got alert. Their darting arthropodic gaits suggested they were spiders, and sure enough, when a few held still momentarily, I saw they were little wolf spiders.

They were probably juveniles that spent the winter snugly under the grass and snow, insulated from the cold. The warmer temperatures and higher sun probably alerted them to get going, as they do many creatures, including trees. But, I wondered for the 10,000th time, what are trees and spiders thinking when spring wakes them up? How do they know what to do?

“Thinking” is a pretty problematic word in this context. A handy default reply to these questions is “instinct.” Which means something like a preprogrammed biochemical response to a stimulus, and implies mindlessness. Spiders and trees certainly respond to their surroundings, but the assumption they are mindless is also problematic. Studies have shown that trees may grow their roots with some kind of intentionality. And very few animals are “dumb,” as per the phrase “dumb animals.” As Edgar Allan Poe said after watching his cat teach herself to unlatch a door to get out, “the boundary between instinct and reason is of a very shadowy nature.”

It has seemed to me for a long time that a lot more than automatic pilot is happening in the tiny neurological systems of spiders. And it turns out that the evidence for their being decision-making individuals is expanding. Here’s a short list of things studies have revealed over the last few decades of what spiders are … thinking?

SPIDERS CAN LEARN

Individual Portia fimbriata jumping spiders, which live in Australia and Southeast Asia, devise plans to capture prey case-by-case. They stealthily survey a scene, such as another spider in its web, then plan a route to a point of attack. Sometimes the route takes Portia out of visual or vibrational range, meaning she seems to have a representation in her mind of what she can no longer see. She has a mental map.

Arachnologists Robert Jackson and Fiona Cross observed that Portia uses vibrations by trial and error to draw potential prey out of its web. Vibrations through silk and other mediums are a common mode of spider communication. “Alternatively,” the researchers say, “Portia may move in slowly for the kill while making signals derived by trial and error that keep the victim calm and stationary. Calming effects might be achieved by monotonous repetition of a habituating signal, as though Portia were putting its victim to sleep with a vibratory lullaby derived by trial and error.”

In a different experiment, some engineers in Great Britain wanted to learn about the mechanics of a jumping spider’s jump. So they trained a regal jumping spider, Phidippus regius, to leap level, ascending and descending platforms, and filmed the leaps. A strange aspect of this experiment is that the researchers did not use bait to get the spider to jump. Instead, their report states, “the spider was manually transported between the take-off and landing platforms until it became familiar with the challenge. No form of stimulation (e.g. air blowing) was used to induce a jump. The spider did not fail any of the jumps; it was either a jump or no-jump situation.”

In other words, the spider learned from the engineers how to make the jump.

SPIDERS CAN REMEMBER

The bowl-and-doily spider, Frontinella communis, which we have here in Maine, in experiments was allowed to catch prey, then the prey would be taken away. Most of the spiders would then search for the lost prey, for as long as 40 minutes; they searched longer for larger prey. They also distinguished between the particular item they were looking for and older remnants.

As observed of the raptor dinosaurs in “Jurassic Park”: “They remember.”

SPIDERS CAN COUNT

The golden silk orbweaver, Trichonephila clavipes, which lives in the tropics and subtropics, also searched for missing prey in experiments.

The researchers also found that the more prey were missing, the more the spiders searched. This implies the spiders keep track of the number of prey in their larders. They can count.

In another experiment, researchers observed how young Portia africana jumping spiders decided where to settle in proximity to the webs of flatmesh weavers that the jumpers typically prey on. It turned out that the jumpers clearly preferred to settle where one other young jumper had already settled; they were significantly less likely to settle where no other jumper was, or where two or three already were. It had nothing to do with available space.

The spiders counted each other.

SPIDERS COMMUNICATE 

It is well-established that spiders communicate. Some spiders with very good vision, notably jumping spiders, communicate in mating rituals with elaborate displays of male body colors and what amounts to dancing. Some of these spiders also produce sounds through stridulations of the legs and through tapping, more or less rhythmically, with the legs or abdomen.

Communication through vibrations, especially through silk, is more or less universal among spiders, and in some cases at least, the meaning can be quite specific. Among cellar spiders (Pholcidae), for example, a mated male and female may co-habit a web for some time, and when one of them returns to the web after venturing out, plays through the silk a message signaling, basically, “It’s me, don’t eat me.”

SPIDERS WITH PERSONALITIES

Most spiders live solitary lives, but a few hundred species (out of at least 49,000) live in colonies; they’re called social spiders. Studies of the African velvet spider Stegodyphus dumicola showed that the longer a given individual spider lived with and had social interactions with other spiders, the bolder that individual tended to be during disruptions to the colony. In another study, S. dumicola’s cousin, Stegodyphus mimosarum, showed greater shyness among individuals after disruptions.

In both cases, the researchers concluded, there were individuals with “more pronounced personalities.”

SPIDER AESTHETICS?

Some spider species, like the garden spiders we have abundantly in Maine, spin a squiggle of heavy silk called a stabilimentum into the center of their orb webs. There are theories about what the stabilimentum does, but no certainty. Arachnologists routinely refer to it as a “decoration,” as if the spiders are making art.

No one knows if this could possibly be true. But there is a species of trashline spider, Cyclosa confusa, that arranges detritus in its web to resemble its own size and shape, presumably as a decoy. A few years ago, researchers found spiders (believed to be new species of Cyclosa) in the Peruvian Amazon and in the Philippines that use the detritus to construct detailed effigies of themselves.

A regular Backyard Naturalist correspondent with background in biological science has told me he’s skeptical of the idea that spiders have “personalities.” But how all the above could happen by “instinct” alone seems equally to defy conventional scientific logic. As Charles H. Turner observed in 1892, just as arachnology was getting its legs (so to speak): “We may safely conclude that an instinctive impulse prompts gallery spiders to weave gallery webs, but the details of the construction are the products of intelligent action.”

Spiders, like Poe’s cat, have minds.

Dana Wilde lives in Troy. You can contact him at [email protected] His book “A Backyard Book of Spiders in Maine” is available from North Country Press. Backyard Naturalist appears the second and fourth Thursdays each month.


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