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Northern Minnesota phenology: Orb weaver spider

By John Latimer

Have you ever walked out on a cool summer morning and found yourself dazzled by the dew sparkled web of an orb weaver spider? Stand and marvel at its beauty and complexity while thinking how on earth does something with a brain the size of a pinpoint create such an astonishing trap? Coupled with the fact that most of this construction is done in the dark by a spider that is for all intents and purposes blind, and it becomes even more amazing.

Orb weaver spider. CC-licensed photo by Emmanuel Huybrechts (source)

Orb weaver spider. CC-licensed photo by Emmanuel Huybrechts (source)

Does she have a plan in her head? Can she imagine where each strand will go? Does she have a sense of what her surroundings are? Each web will be different requiring different lengths of silk and a differing number of radii. Remember she has such limited eyesight that she must monitor her web through her sense of touch. In much the same way we can triangulate a sound coming to our ears and know what direction it has come from the spider can feel the vibrations in her web and know where her victim is. Not only which direction it lays but how far out the web it is. Scientists have plucked the web at various locations and observed the spider unfailingly run to that exact spot. Further she can catalog and remember several different locations at once. When they plucked the web in three different spots she was able to accurately check out each disturbance. There must be something more than stimulus and response going on here. So how does she do it?

Climbing to an elevated position she lets out a fine line of silk tipped with a bit of glue. Aided by the wind the line drifts until it strikes some object. The spider quickly secures her end and dances across the line while laying out a second heavier line. Once she has this line secured she traverses back to the center of the heavy line that sags under her weight. Near the center she attaches another line and drops down seeking a third point of attachment. When she finds that third spot she has constructed a sort of “Y” shaped framework. Now she has the basis for her web.

Climbing to the top of one of the legs of the “Y” she either climbs or drops down and secures this piece of the outer framework. Next she attaches a line to the center of this segment and works her way back to the center where she pulls the line taut and secures it. Continuing in this manner she establishes both the outer edges and her radii within the web.

Once all the spokes have been laid out she establishes scaffolding that will aid her in making the final web. Beginning at the center she spins a widely spaced non-sticky spiral of thread that will guide her as ultimately completes her task. With her walkway in place and starting from the outside she puts down a sticky tight spiral of silk designed to catch and hold her prey. As she does this she eats the walkway threads to recycle them later.

Orb weaver spider

Orb weaver spider. CC-licensed photo by Bob Kingsley (source)

Observing these webs you may notice that the center sometimes has a nice neat hole cut into it. Or that she has discontinued the sticky spiral short of the center. This allows the spider to quickly switch sides of the web depending on the location and size of her prey. If the captured animal is large she may choose to approach it from the opposite side of the net in order to bite it without placing herself in danger. Some large prey may take several bites to inject enough poison to subdue the meal.

The other thing you may notice in some of these webs is a bit of white silk zigzagging near the center. Not all spiders add this bit of decoration called a stabilimentum, but it is present in many webs. Opinions differ as to the purpose of this construct. Some think it is a way for the spider to alert birds about the location of the web. Others speculate that since the silk is visible in the ultraviolet range of the spectrum and insects can detect these wavelengths it may act as an attractant. Often times the spider herself may use the stabilimentum as a hiding place. Whatever the purpose it adds a bit of interest to our observations. While you look at these amazing traps think a bit about the spider and how she may perceive her world. Think about what might be going on it that tiny little brain of hers.

From the phenology notebook:

June 2, 1990: Canada anemones are starting to bloom in the ditches. Because they are rhizotamous they are always seen in great clumps, and given their large five-petaled white flowers they are hard to miss. The red pines are starting to flower and at their feet the starflowers are blooming. Wild columbine, mistakenly called honeysuckle by nearly every kid in Minnesota, has begun to bloom. Those five red spikes tipped with nectar are known to many a child and not a few hummingbirds as well.

June 13, 2006: My son Martin and I watch fascinated as an orb spider spins her web. She strings the spokes first and then circles the structure stretching the silk with her leg and then quickly dabbing her spinnerets to attach the line to the spoke. While she was doing this she stopped to eat some silk that was in the center of the web. After that she continued to build her web until a fly came along and was captured. In seconds she had immobilized it with a bite and wrapped it in silk. Along the edge of the lake we watch as a mob of tadpoles attack the rotting carcass of a sunfish. Yarrow has begun to bloom.

June 25, 2010: The roadsides are becoming quite colorful with the blooms of many summer flowers. The magenta fireweed and the bright yellow of the black-eyed susans set off by the lush green make for wonderful sights. The butterflies and day flying moths are starting to find the first spreading dogbane flowers. Lovely small bells of white streaked with pink these are very popular flowers with the nectar drinkers. The first goldenrods are budding. It won’t be too long and they will bloom.

 

John LatimerJohn Latimer is well known throughout northern Minnesota for his phenology work.  John appears weekly on KAXE radio in Grand Rapids, and audio and twitter archives are available here. We hope his work will be a frequent feature on MyMinnesotaWoods.  This article also appeared in the Duluth Senior Journal.  It is printed with the author’s permission.

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