each unique to the spider who built it

To many spiders, the web is everything.
For the approximately 15,000 species of web-building spiders, most of them nearly blind, the web is their essential window on the world: their means of communicating, capturing prey, meeting mates and protecting themselves. A web-building spider without its web is like a man marooned on an island of solid rock, totally out of touch and destined to starve to death. A fly could walk unmolested right under the nose of a webless spider.
Perhaps no one knows this better than Dr. Peter N. Witt, a physician-pharmacologist who 37 years ago was seduced into a career-long study of spiders and their silken domiciles. In 1948 a frustrated zoologist at the University of Tubingen in West Germany turned to his pharmacologist colleague for help in photographing orb-web spiders in the process of constructing their homes. The spiders normally perform this task in the dark around 5 A.M., which is not exactly ideal for movie making. The zoologist wondered if his subjects might be drugged into changing their construction time.
Young Dr. Witt had no trouble feeding the spiders sugar water spiked with various stimulants or tranquilizers ... but the movie-making zoologist was not exactly pleased with the results. The drugged spiders still built their webs in the early-morning darkness, and now the resulting webs were bizarrely abnormal, as if built by a drunk.
The zoologist abandoned the movie, but the pharmacologist was hooked. Here, he explained in a recent interview, was a reliably reproducible means of assessing the behavioral effects of drugs with mind-altering potential. Each drug seemed to produce characteristic aberrations in the spiders' webs, changes far more reliable than the behavioral effects of drugs observed in laboratory rats or human subjects.
Since the orb-web spider builds a new web each day, it was possible to do repeated tests of different drugs without having to collect and house thousands of spiders. Dr. Witt's detailed analyses revealed that while all orb-web spider webs look basically alike, each is unique to the spider who built it. In fact Dr. Witt was soon able to identify escapees by their webs. The webs also reflect genetic relationships; those built by sibling spiders are more alike than those constructed by cousins.
Jane E. Brody, writing in the 9/17/1985 NYT.

Webs made by drugged spiders photographed by Dr. Peter Witt: 1. undrugged,  2. benzedrine,  3. caffeine, 4. chloral hydrate.

Witt's photos via Neuroscience Art Gallery. More here + here.