What are cobwebs? And why do they appear in houses? What does a multiplicity of cobwebs mean?
As regards cobwebs, the word cob has nothing to do with corn! It probably originated with an Old English word - "COPPE," which meant spider. So the word "cobweb" might just be a sloppy way of saying coppweb.
Cobwebs look like hanging clumps of silky spider web material. That's what they are! They are what is left after a spider abandons a web. It may be that the spider sabotages a couple of the structural, hanging points of the web so no other interloper can take advantage of the web being abandoned.
What kinds of spiders produce cobwebs? Are there "cobweb spiders?" Yes, and they make up the family Theridiidae. One of the most common house spider in the United States is Achaearanea tepidariorum, of this family. The infamous Black Widow spider, Latrodectus mactans, also belongs to this family.
On the particular inspection in the photos above I encountered a number of black widow spiders and what looked like their egg sacks.
Some cobwebs may not be a part of a previous web at all. They may instead be a purposeful, hanging clump of silky web material intended to safely house many egg sacks. Other insects will not bother the eggs as they know what will happen to them in the web!
As they hang there, over time and in the blowing air current, the cobwebs gather dust and become more and more visible.
What does a multiplicity of cobwebs mean?
Simply that the location is a habitat that can support many spiders!
Spiders need moisture, which they can always go outside to obtain, and a food source.
The larger the food source the more abundant the spider population will become!
This house was unkempt, to say the very least, and therefore full, and I mean FULL, of roaches. It also had a serious termite infestation.
If spiders are well fed, their basic objective in life is to do what all fauna do, make more spiders!
And as the habitat provides more and more opportunity, the spider population will increase.
Spiders build webs near moving air. They do that instinctively. If the air is moving it is hoped an insect will fly by. The web is built to capture as much of the air current as possible, in the continued hopes that it will capture food.
If the web comes up empty for a period of time, it will be abandoned. And maybe partially dismantled.
However, if another spider senses that this is a good place for a web, it will ignore the fact that a previous web was made and build a new one.
That one might be abandoned as well, and the cycle continues. Eventually there is a multiplicity of cobwebs, getting dirtier and dirtier with floating dust, and more and more visible.
Of course, if the food is crawling by that is good too! And I can confidently say that a LOT of food was crawling by in this house!
My recommendation: when you see a cobweb you know there is a moving air source that encouraged a spider web. A web can be built quickly, even overnight, and you might not even see it until it is abandoned and begins to collect dust. However, you may want to investigate the reason for its placement. There is moving air nearby! That moving air may be because an HVAC register is blowing air in that direction, but it may also be a gap in the exterior skin or around a window or door that should be sealed for energy efficiency also.
Jay Markanich Real Estate Inspections, LLC 
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560
Too much information LOL. Great post Jay. I never realized the relationship between spiders and other creepy things like roaches. I hope this house was a really good deal!
It is intended at the moment for demolition Anne! The house was a disaster! The purpose of the inspection was to give the County ammo for condemnation.
"you might not even see it until it is abandoned"????
Or, walk right into it!!
Lenn - as much as I tried to avoid them, I was walking into them all day! My fear was that a black widow would drop onto my ear! I don't usually bring my motorcycle helmet to inspections, but maybe I should start?
Due to HI's bringing out 95% of them out of the crawlspace our faces & everywhere else, maybe we should start charging extra for Cobweb Cleaning :)
I like learning new things and here at the rain I learn something new each day like today
I'm with you Joshua! And I really don't like using my head for that!
James - that's it in a nutshell, isn't it!?
I freak when I walk through a web in a basement. Or a vacant house. I do not envy inspectors crawling through crawl spaces with crawly things. I always wondered if the cob part of cobweb had to do just with the abandoned webs that catch dirt. Is an active spiders web a cobweb? I have been wondering this since I was a kid, looking at cobwebs in the barns at my grandpa's farm.
Roaches really, really scare me.
I walk through them too, Maureen, before they have collected enough dust to become more visible. A spider web isn't technically a cobweb until it is abandoned.
Glad you enjoyed the information!
Jay, this really creeps me out, sorry. Although now you have given me a better education about cobwebs. I keep a baseball cap in the car to go into basements that are creepy.
Now I will be itching all day.... thanks...
Andrea - if you lick them they taste like chicken.
You might not want to believe that...
Thank you Jay for sharing everything I did not want to know about cobwebs...interesting...but icky...
But Ginny, think how good you'll look if a related question ever comes up in a Trivial Pursuit game!
Jay, I didn't just fall off the beet wagon ya know...
I have had the dubious distinction of being bitten on 2 separate occasions by brown recluse spiders. 2 bites by 2 spiders on my leg, and one on my chin... painful bites and I was lucky on both occasions that the bite didn't result in massive scarring or any flesh eating type of icky stuff. (technical term there)
All spiders must pay. When I was milking cows on a regular basis.. we would have some pretty big ones come in to the milking parlor. I would take my hose, aim it like a gun and shoot them with a very hot, very strong stream of water and watch them jet ski their way into a new existence. When it comes to spiders, Buddhist I ain't.
If Billy Jays comes up with an anti spider suit, let me know, order me 3 or 4...
Gee, haven't you said that to me before Andrea? Wow, twice by a brown recluse! Yikes!
I will have to contact Billy and see what he thinks about this suit idea...
Oh my, what a nightmare to have so many. Yes, this house has provided a ton of blog fodder. Thx for the education on cobwebs.
This house was a disaster in many ways Debbie. Hopefully, for the homeowner, it will be a disaster yet in the future as it is leveled. And you're welcome! You scratch my learning itch too!
Can you get a little down and to the left...?
Moving air you say...hence the "clean the cobwebs" from someone's head might imply there were more holes than necessary.
Gross! You're the MAN
Where there are cobwebs there are spiders. Needless to say I don't envy your job at all.
S&D - not bad! Empty headed might lend itself to more moving air!
Ken - not really. Just doing the job!
Cindy - next one of these I will call you and we'll go together. Remember to duck.
Interesting information. I never really thought much about spider webs - other than avoid them!
Thanks Gary! We have lots of them here. I don't know about there! I expect the lizards are good at keeping them out of the house.
Say hi to my cousin in Rockledge - Robert Chaffiot!
Jay, with Halloween coming up, a lot of us are thinking about cobwebs! Great timing for this post.
Maybe I should have waited, Pat, until closer to Halloween! But it's out now. No pulling it back!
Jay, with all the different things you must walk in to in a home inspection, what makes you the most uncomfortable?
Great article Jay, useful information for home inspection.
Chris - a seller who is present who demands to be a part of the process and tries to direct traffic.
Thanks Will. I am glad you can use it!
I swear I see Charlotte---I know she must be hiding in there somewhere!
There were a whooooole bunch of them Charlie. And most of them were black...
Jay -- wow, an incredible dissection of the spider issue. Very appropriate for an October post with Halloween just around the corner.
Michael - someone earlier suggested that I should have waiting until around Halloween to post this!
The theme and information, as always, is great to read! This and the gravestone history would make great Halloween posts. I think I have said it before... I thoroughly enjoy your blogs. ~ jennifer the IHI Office Girl
Thank you Jennifer. And I'm glad you do. Keep reading and when you go around your house you might recognize some things to do or pay attention to! (Not that you cannot get that around the office...)
When I bought my house there were a lot of spiders around the exterior. This was because of all the trees that were close to the house. I have gotten rid of most of the trees and a good number of the spiders too. Take away the conducive conditions and away go the bugs and so go the spiders.
Remove the food, remove the spiders! Good reasoning Jim. When we moved in there were hundreds of garter snakes around one section of the foundation. We found out later that the house was built on what used to be a favorite breeding location for mice, which were no longer there. The snakes left.