Hot Topics: Is a Rat Eating the Insulation?

A rat on a piece of plywood.

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Original Post: Is this rats or something else?

dm888 Member

I thought I would start a new thread here and include a picture because now I am not sure what I am dealing with. To recap, a couple of weeks ago I got my crawl space cleaned out and they only insulated the ducts with unfaced insulation, secured with twine. In that short period of time, something got back in there and is shredding the insulation off of a section of the duct and creating a huge pile on the ground. Due to the size of it, I am wondering if rats are even capable of doing this or if it could be something else like a squirrel. I do know where it is getting in and out as there is a good-sized gap of about three inches by 12 inches long, part of which I have blocked off now. I shoved some paper in there and when I checked back, it was moved within a day or two. I have five traps set inside now and six outside, along with a bait box. The bait box has a brick on it, yet something managed to move it the other day so I put a bigger brick on it. I also put a cage trap inside for a few days in case it was a squirrel, but thought if it was a squirrel it might be better to put that cage outside, so I just did that. Take a look at the picture and let me know if a rat could have done this much damage in two weeks.

PAbugman Forum Topic Moderator

That's a serious pile of insulation. Rats typically tear up just what they need to enter or exit. This does appear to be larger. I once saw the damage that a ground hog did to fiber duct and this reminds me of that. I suspect that you have a similar sized animal in there, although squirrels do a lot of damage, too.

Does any part of the structure cantilever out overtop of the foundation wall? The groundhog I referenced was coming in over the top of the foundation wall, but underneath the cantilevered part of structure as there was fiber board where plywood should have been.

dm888 Member

Here are a couple more pictures to help illustrate it better. This shows the outside of the crawlspace. There is no poured foundation as this room addition is on posts, but I enclosed it with plywood. Above the conduit, you will see some screen between the plywood and the joist which sits out a few inches from the edge of the plywood. Apparently, I missed screening a section way down at the far end as you can see here. It is a few inches wide and it looks worn/rounded. I shoved that piece of paper towel in there two days ago and yesterday it was still in place, but today it was moved so something came in or out. It doesn't show well in this picture, but to left of that downspout is a partial concrete wall so they could either go on top of it and hop into that hole, or climb up from the ground as seen in the other picture. I am in Washington state and I don't think there are any groundhogs here, but plenty of squirrels. I hope this helps.
PAbugman Forum Topic Moderator
If that is the entry/exit point than this animal(s) can't be much bigger than a squirrel. If you can cover that portion with screen, then the animal will be effectively excluded. The kicker is that we want it to be excluded, and not trapped inside.

I know that the bat exclusion people use mesh/rubber/tarp, etc. and hang it along the areas where bats enter/exit for the purpose of acting as a one-way valve or excluder. There may be a solution in that, although we won't know if its gone. I'll continue thinking about this.
dm888 Member
Correct. Once I seal that up, it should be excluded. I was thinking of a one-way type of door, but didn't know how. Would you conclude that this is most likely not a rat, though? I have a cage trap set with peanuts outside for now in case it is squirrels.
You're just going to have to trap for both rats and squirrels. I had both in my attic. It took a long time to get them all out. I suggest peanut butter rather than peanuts as bait. A crafty squirrel might be able to lift the peanuts without setting off the trap.