Thursday, July 9, 2009

Orbweaver Spiders

Nature Watch

By Susan Benson,
CNHM Director of Education
This week, on most mornings during or after the rain or dew, spiders webs were quite visible. Drops of water highlighted their presence. One spider I observed had built it’s web in what I thought was the most unlikely place, between my screen and storm doors. Who would guess they could catch something in that space? Nonetheless, spiders are amazing with the webs they weave. Orbweavers are best known by their beautiful webs, made at night in many different habitats. They are obviously known by their spiral, wheel-shaped webs, and are enjoyable to observe.

The making of an orbweaver web is an engineering feat, begun as the spider sends out a line on the wind to another object. Once the new line is secured, they drop a line from the center, making a “Y” shape. They then follow with making the “bicycle spokes” with a non-sticky silk. The final spiral is made with a very sticky capture silk. They keep themselves from getting stuck in their own web by traveling on the non-sticky part of the web. Usually the prey insect that is caught in the sticky lines is paralyzed by a quick bite and then wrapped in silk, or if the prey is a more dangerous insect, such as a wasp or bee, they may wrap the insect before biting.

With very poor vision, orbweavers must sit near or in their web to feel the movement of their prey. When caught, the front legs turn the insect while the back legs wrap their victim with silk. Many build a new web every night.

Orbweaver spiders show impressive brain power and web strategies. If researchers vibrate a web at multiple points, and then remove the stimuli, this spider moves to one point to check if an insect is there, and then moves to the next point with only their memory to guide them. Orbweavers have the ability to memorize multiple coordinates in their web. Web construction itself happens mostly at night, also suggesting that a spatial representation exists. That they can build a web using drops of “glue” and heavy gauge silk line as strong strands, followed by sticky inner catching threads is impressive architecture. Imagine building a house without using your sight!

For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility and exhibits, the Curiosity Center and Brain Teasers 2, in Cable at 13470 County Highway M. Also find us on the web at to learn more about exhibits and programs.

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