The majority of cobwebs are actually formed from abandoned spider webs. These home-abandoning spiders, mainly those of the species Theridiidae, build these sticky webs for catching prey.
Cobwebs are terrific reminders that it is time to clean the difficult-to-reach spots in your house. These pesky webs form in the corners of our rooms, along the edges of ceilings and on the sides of our walls. You can get rid of them easily, but without fail, they seem to come back in no time at all!
The common assumption is that these cobwebs form out of the blue, due to dust particles adhering to each other (maybe they’re just lonely), but cobwebs don’t spontaneously form. The real secret behind cobwebs is actually far creepier.
Cobwebs are the work of spiders
As it turns out, the majority of cobwebs are actually formed from abandoned spider webs!
Web-building spiders create elaborate webs for catching prey (wandering spiders chase after their prey, rather than building webs). Over time, however, mechanical stress and dust accumulation weakens the web, forcing the spider to abandon it and build a new one. That’s why you never see a spider on a cobweb, even though the eight-legged arachnid is responsible for its creation!
The word cobweb comes from the Old English, from coppewebbe, originating sometime around the 14th century. Coppe comes from attercoppe, which means spider or more literally ‘poison head’. Web also finds its origins in Old English, and means tapestry or something intricately woven.
Theridiidae or the Cobweb spiders
Taken literally, cobwebs are just old spiderwebs, but one family of spiders got the top title – Theridiidae or “cobweb spiders”. These home-abandoning spiders—forming one of largest spider families, with over 3000 species—get their name from their distinctly disorganized webs. Their tangled web formations don’t have any discernible pattern. The different species have different disorganized patterns of web-building, but there are some overall commonalities.
Image Caption: A spider from the family Theridiidae weaving a cobweb
Most are adept hunters and those that do make webs to catch prey intentionally make them a tangled mess. They anchor their webs to support structures, like beams and corners of walls, building a 3-dimensional snare. This snare then ends up as a common household nuisance once it serves its meal-driven purpose to the spider.
The ends of these webs, when they are active, have sticky droplets to glue unsuspecting insects (like flies) to the web. The same sticky property of the web also attracts dust and pollen, agents that tend to damage the web.
Other web-building house spiders:
Theridiidae aren’t the only spiders that use the corners of our houses to build their nests. There are a few other spider species whose webs you might find in your home too!
One group are the ‘daddy longlegs spiders’ (not to be confused with the other 8-legged daddy longlegs that live under rocks and is NOT actually a spider). Once called cellar spiders, they belong to the family Pholcidae. Their webs are also found in corners of ceilings, underneath stairs that or other unfrequented spots in your house. Their webs are irregular and could easily be confused for being a cobweb spider’s web by an untrained eye. However, their webs have slight differences in structure.
Some webs might have a funnel, tube-like shape that is spread out like a sheet. These webs can be attributed to funnel web spiders, which consist of a few different species. Their webs are mostly found in dimly lit areas like storage rooms or in boxes and closets.
The last spider worth mentioning in this article are the orb-weavers, noted for their geometric circular spider webs. This web is the one that graphic designers might use to demonstrate an ideal web. Part of the Araneidae family, they are found more often in gardens and on trees, but sometimes end up in homes as well.
What About Single Strands of Dust?
Okay, so now we know that the haphazard cobwebs were once active spider webs, but what about those single strands of dusty material that are seen hanging from the ceiling? Are spiders responsible for those too?
In fact, they are. Spiders, as well as a few other tiny arthropods, have the ability to produce silk strands for travel and protection. Spiders specifically use this strand of silk as a safety line when they jump or swing from place to place.
The technical term for spiders traveling using silk is ballooning. It’s a bit like Spider-Man, if you think about it. Or rather, Spider-Man behaves like spiders!
These silk strands are different than those the spider uses to make webs. The silk they use to balloon is dragline silk, also called ampullate silk. This is not the only use of dragline silk, but it may also sometimes be used as a scaffolding for the web.
Again, these left-over strands of silk gather dust over time, resulting in those single irritating dust strands that we’ve all walked through and then had a tiny panic attack while trying to pull them off our face.
Don’t cobwebs degrade?
An even more fascinating curiosity is how long a cobweb lasts. Spider silk is a tough, strong, and hardy material. Scientists have been trying to replicate its tensile strength and elasticity for quite a while now. This strength also gives it certain immunity from degrading.
Though dust and pollen harm the web, making it useless for the spider, it doesn’t just crumble after the spider isn’t there to tend to it. A team of scientists studied the strength of 4-year-old abandoned spider silk and found that though its mechanical strength had reduced, it was still surprisingly strong.
Spider silk can be degraded by enzymatic action (spiders can eat their silk, after all), but environmental degradation is much slower. The silk strands are made of complex amino acid crystalline structures that make the silk very durable.
Spiders are the secret behind the dust streamers casually decorating our homes. As strange as it may sound to some people, perhaps spider enthusiasts may find cobwebs interesting, as they can be used to track the movements and web-building habits of spiders. Or maybe not.
Spiderwebs are very difficult to spot due to the razor-thin strands of which they’re made, and by the time you do spot them, the spider is likely gone and the web is already lined with dust, abandoned for a newer, more invisible home!