Spiders are, among other traits, famous for their ability to craft intricate, beautifully designed webs of silk. While spider webs can be indeed creepy and unnerving, especially if you walk right into one, they are nonetheless absolutely amazing feats of design work.
Different species of spiders create different types of webs, from the iconic spiral web shown here to sheet webs and even funnel webs. In fact, according to About Education, some spiders even add "decorations" within a web, which are called stabilimenta. "A stabilimentum may be a single zigzag line, a combination of lines, or even a spiral whorl in the web's center. A number of spiders weave stabilimenta into their webs, most notably orb weavers in the genus Argiope."
The question, though, is why do spider webs have designs at all, and aren't just a mess of sticky silk hung willy-nilly from some tree branches?
It turns out it could be for a number of reasons. Stabilimenta are thought to have purposes including making the web more visible to non-target species (like humans!) so the web is a little more protected from accidental destruction; camouflage so that the resting spider itself is hidden within the design; or attracting prey to a certain part of the web. But the overall design, stabilimenta included, comes down to stability. As we know, spider webs are incredibly strong, and the designs add extra strength so the labor-intensive structure isn't entirely destroyed by a large, struggling bug. But it's not simply about brute strength -- it's also about how the strength of the structure works as a whole.
Spider silk is, pound for pound, stronger than steel. A study by researchers at MIT showed that it is not only the strength of the silk and it's ability to both stretch and tighten with different pressure that allows a spider web to resist damage, but also the intricate design of the web itself. "Spider webs, it turns out, can take quite a beating without failing. Damage tends to be localized, affecting just a few threads — the place where a bug got caught in the web and flailed around, for example. This localized damage can simply be repaired, rather than replaced, or even left alone if the web continues to function as before."
Because webs are designed in a way that damage stays localized, a spider can more easily repair a web rather than having to entirely rebuild it after every single impact from a bug, twig, or strong wind. For a spider, taking extra time to design a web means saving energy down the road.