Fascinating Facts About Spider Webs

Spiders are incredible creatures. These venomous arachnids are found all over the world and range in size from the .011-inch Samoan moss spider to the massive one-foot-wide Goliath birdeater, which eats not only birds but frogs, rodents, and a staple of insects. Possibly the most commonly recognizable aspect of spiders is their silk webs.

While most people may hold a generic image of spider webs in their minds — circular, delicate gossamer-like structures woven into intricate geometric patterns, just waiting to get tangled in the hair of the unwary dog walker — they can take many forms. Their purpose can also extend to far more than just catching flying insects, and the very material they are woven from — silk — has a multitude of essential roles for spider survival, too.

Spider webs and the silk they are made from are biological wonders, ones that scientists continue to study closely. Arachnophobes beware, but if you're not too creeped out yet, here are some fascinating facts about spider webs.

Spiders live a complex life of catching prey, building webs, dropping from heights to startle you, and reproducing. To perform these various arachnid activities, silk is necessary. Spiders produce their silk through their spinnerets, but amazingly, not all spider webs are created equal. Spinnerets can produce seven types of silk, which are each used for different purposes (per The University of Bristol).

A specific type of silk is used for wrapping prey, another is used to form egg sacs, and silk of a yet different composition makes long, non-sticky draglines — these are the kinds mainly used to build webs. Some spiders can even produce silk that acts like cement. To generate each type of silken thread, spiders are able to control the combinations of proteins used, secreted from various glands.

No species of spider yet found can make each type of silk, of which seven are known, although all spiders produce the tough draglines. Which kind of silk a spider can spin depends on the species and also sex. For example, only female spiders produce the silk that is used to make cocoons. 

The kind of spider web most people are familiar with can be found in any garden, and their function is also well-known. Strung taut between supports, such as tree branches, they are held aloft in wait for flying insects. However, spiders have been using silk for some 300 million years, and the webs we recognize today were not the first use of silk.

Spider experts, like William Eberhard in "Spider Webs: Behavior, Function, and Evolution," explain that spiders originally spun silk to create their egg sacs and to line burrows. Primordial spiders did not hang out in webs, but waited in their burrows for a victim to wander by. In time, the silk that extended from the den became a kind of sensor that alerted the spider to the presence of prey. It is believed that larger and more elaborate spider webs were an extension of this, since they provided the spider with a greater range to capture prey and sense nearby enemies.

Some spiders still use this tripwire system, such as the highly poisonous funnel-web spiders found in Australia. These spiders live in dens, under rocks, or in crevices. To catch their prey, they lay out silk in an irregular pattern of trip lines. When a meal stumbles into one, the spider charges out, injects it with venom, and drags it back to its den.

One of the most remarkable abilities of spiders is that they can use their silk to fly. Using long silken strands, spiders are lofted into the atmosphere in a technique called ballooning. In fact, some spiders can reach heights of 2.5 miles, right in the jet stream. Ballooning allows some species of spiders to travel incredible distances. For example, Science News reports that the ancestors of a species of trapdoor spiders probably traveled from Africa to an island off Australia by wafting on spider silk. Spiders use ballooning to expand their range and settle into new territories.

While ballooning is fascinating in itself, a recent study published in Current Biology shows that some species of spiders can use this technique with Earth's electrical field. In experiments, researchers found that some species of spiders ballooned when placed in a chamber with no airflow but containing an electrical charge, using the electric field as a means of takeoff. While these spiders may seem to have preternatural abilities, it is all biology. Spiders detect the electrical field by hairs called trichobothria, much like how human hairs spike up from static electricity, but far more sensitive.

Spiders can build homes that, while not palatial, protect them from the elements. For example, many spiders use their silk to create lining for shelters. For example, funnel web spiders in Australia typically inhabit cracks and crevices near building foundations and line them with webs.

In other places, the silk becomes even more critical for survival, and one of the most extreme examples is the Himalayan jumping spider. These little creatures are most likely contenders for winner of the terrestrial animal who lives at the highest elevation contest, with specimens found as high as 22,000 feet, on Mount Everest. 

Such elevations produce extraordinarily harsh and cold conditions. To survive, these spiders use their webs to create makeshift shelters by spinning silken chambers or cells among the rock falls. Food is scarce, but this species manages to eke out a living feeding on insects that come up the mountain to forage on vegetation blown up by the mountain winds. The entire ecology, an Aeolian biome, is dependent solely on windborne particles of food — and at the top of the food web, thanks to its snug alpine web nests, is the jumping spider.

When a spider gets busy making a web, it extrudes silk from spinnerets located on its rear. This fascinating process involves an impressive feat of biochemistry, where the stored spider silk undergoes an instant phase change. 

The stuff that becomes spider silk (called "dope") is kept in liquid form before being used. Research published in Science Advances explains how dope passes through channels in the spider's body to the spinneret. In doing so, the protein-laden liquid, which is comprised of individual structures called spidroins, self-assembles. It folds and interlaces to instantly form spider silk. 

More remarkably, the spider can choose what type of web to spin at will, ranging from ultra-strong draglines to an egg sac. The trigger for determining what kind of silk occurs when the dope is exposed to acid as it exits through the spinneret. Meanwhile, the substance is lengthened and linked up through countless ducts which continuously narrow. This process, built upon millions of years of evolution, is extraordinarily complex, and the method by which spiders spin their webs varies from species to species. 

There are many species of spiders that, when mating, the male is eaten by the female. Black widow spiders, for example, earned their name from this behavior. Although many male spiders seem to prefer to die while mating, some would reasonably prefer not to be cannibalized, so they employ their trusty spider web skills to survive their date.

For example, males of species such as Ancylometes bogotensis and Nephila pilipes are many times smaller than the much more aggressive females. The males use their silk to tie up the females during courtship to protect themselves. The silk can be used as a light covering of pheromone-soaked silk, or a more substantial bond for the legs. In all cases, this activity only seems to be intended to calm the female, which facilitates the mating process. In this way, the calming function of the silks seems to be more important than the actual physical restraint — after all, the female spiders can break out of the silken bonds quite easily when mating is finished.