That zig zag down the middle is called a stabilimentum. Some web building spiders incorporate these into their webs leaving scientists puzzled for years. There have been and still are many theories for this decoration, which may take several forms from a circular pattern to zig zags in the corners, to a row down the middle of the web.
Depending on who you ask and where you look, you will likely find many theories to this age-old question. Perhaps the best answer is that we don’t know for sure AND there may be more than one theory that is correct. The last theory below is the one that has come about most recently and is thus accepted by some as THE answer to the question.
Some theories are:
- That the stabilimentum provides reinforcement for the web, or stabilization, especially in instances when larger insects become trapped in the web. Webs with center decorations are sturdier than webs without.
- That the stabilimentum makes the web more visible so that birds and deer and other animals won’t walk into and damage it, thus necessitating the spider to build the web again.
- Another theory is that it provides camouflage for the spider.
- And lastly, another theory says that the stabilimentum actually attracts prey in a way similar to a flower attracting an insect. Biologists studying spiders discovered that spiders who put these decorations in their webs were twice as likely as spiders without decorations to catch insects. They concluded that pollinators such as butterflies, flies, wasps and bees have a greater sensitivity to ultraviolet light, allowing them to find important food sources. Many flowers reflect ultraviolet light in a way that attracts insects, like runway lights for the planes at the airport. In the same way, the stabililmentum reflects ultraviolet light, effectively signaling to insects to come in for a closer look. So the stabilimentum actually ATTRACTS insects! Amazing, right? (To read about a study out of Australia on this click HERE or click HERE for another link about a study on this)
Do you think the last theory makes the most sense?
Insects and spiders continue to fascinate me while at the same time, giving me lots of wonderful subjects to photograph. I hope that next time you notice a web glistening in the sunlight, you will take a minute to truly look at it, and appreciate the beauty.