Trashline Orbweavers: Genus Cyclosa

Ubiquitous spiders, trashline orbweavers show their trash in wooded and residential areas around North America. At the same time, they are also a little known orbweaver.

Size partially explains their dual ubiquitous/unknown status.

Trashline orbweavers often grow less than one-quarter inch in length, placing them in the tiny spider category. Were it not for the stabilimentum (long extra white thread in the second picture) built into the middle of some webs, they would go mostly unnoticed.

The name trashline refers to their practice of attaching the remains of their prey and other objects to the stabilimentum.

The stabilimentum itself remains one of the great mysteries of the spider world. The Writing Spiders, another common stabilimentum building group not all Trashline and Writing Spiders build them.

Initially thought of as a means for adding stability to a web, arachnologists now posit a handful of hypotheses to explain its existence.

An article in the Journal of Arachnology hypothesized that because stabilimentum reflect ultraviolet light similar to flowers, spiders incorporate them into webs to attract insects associated with flowers. The research concludes that trashline webs with stabilimentum attract more insects.

On the other hand, a recent article in the journal published by the Arachnological Society of Japan reported no difference in the number of prey captured by cyclosa stabilimentum webs and cyclosa non-stabilimentum webs.

Differences in research methodologies adopted by the two studies could partially account for different results. The first study examined web capture rates in a natural setting and employed statistical methods to control for differences in web size, web location and stabilimentum versus non-stabilimentum webs.

The Japanese study used laboratory controls for the webs. Two webs were constructed (with a stabilimentum artificially placed on one of them) in a laboratory setting, placed in artificial frames and transported to a field for observation. Furthermore, both webs were placed in close proximity to each other for observation of each web's catch rate.

In the case of the Japanese research, it could be the case that the UV reflectance of the artificially placed stabilimentum faded over the time it was created and the time it was used, creating a control problem for the research.

A limited number of observations for both studies could also have influenced the results.

Finally, it could also be the case that rather than serving to attract prey, the stabilimentum serves as a stop sign, with the intent of deterring birds and animals from walking through it (see Ultraviolet Reflectance of Spiders and their Webs). However, one stabilimentum that serves as bird or animal stop sign could also serve as neon billboard sending a message to other birds or animals that says free food here.

With all the conflicting research published to date, the mystery of the stabilimentum continues.

The top picture shows a side view (enlarged by a factor of at least six) of a species called cyclosa conica. The conical shaped body explains the name.

© 2009 Patricia A. Michaels