Mouse nesting locations in the Prius Prime

Sorry for another mouse thread. I know there are plenty of other mouse threads here, but I thought I will just start my own so that I can keep a record of what I have discovered, learned, and done for the problem. By documenting it here, I thought others may be able to avoid inconvenience and damage by mice (deer mice in particular in my case).

I have noticed a mouse infestation in my only 10-month-old 2021 PP 10 days ago. Over 30 years of owning cars, this is the very first time I have ever actually seen an infestation in our cars. I have heard and read about the problem, but it never happened to our cars. That was until now. Ever since I started working from home, the car has not been driven every day. That must have been one of the major reasons this happened.

The account of the discovery of the mouse infestation in my PP and what I have done so far has been described in another mouse thread blow.
More on Mice... Prius Prime | PriusChat

It turned out, that the first obvious sign that the mouse has entered the engine bay and started to build a nest was the hole on the insulation pad on the hood. When I removed the hood insulation, I found a mound of nesting material on top clearly pointing to the location chosen by mice to build their new home.

Then, later when I checked the cabin air filter, I also noticed that they have gained the access to the filter and decided to use the filter material to start building a second home there.

Well. Today, I found a third location they were planning or may have already finished (?) building a nest. Can someone here tell me what the red arrow is pointing to? The nesting material was found under this component on the metal pan. It is not as obvious as in the other two locations, and I must have missed it when I was visually checking for any damages.



The close-up of the left side of the component above looked like this.


The area is well protected and a number of hoses and wire harnesses are located. Using a wire hook, I was able to remove most of the nesting materials mice had hoarded. But without removing the parts indicated in the first photo, it is hard to say if I successfully removed all the nesting materials. I am not exactly sure where this "white fiber" nesting material came from. It is not the same material as the cabin filter that was destroyed. The hood insulation material is black, so that is not it either. My guess is this came from the underbody cover insulation, but without raising the car and removing underbody covers, I can't confirm it.



I am almost sure, although not 100%, that there are no resident mice currently living in the engine bay. This is because I have taken the car for an overnight trip, and during and immediately after the trip, I did not see mouse activity in the engine bay. Also, I have not seen any mouse activities inside the cabin beyond the cabin filter. What I am seeing are the signs of mouse activities exploring the familiar locations by revisiting the car. The hood insulation was removed for now and not re-installed, and the cabin filter is blocked by hardware cloth now. So, they can't make a nest there again. By the nest described above, I now have removed the third nest. However, this location is difficult to close off or remove. So it remains to be a location where they can potentially resume the nest-building activity again. I wonder how much longer they will keep coming back to the car to explore the relocation place where they want to build their home(s)? It is getting warm now, they don't need much warmth. I am sure there are plenty of other locations on my property where they can find plenty of food and hide from predators and raise their pups. So, why is my car their favorite location???

So far, those methods have been used but have not stopped the nightly visit completely.

1. scent-based repellents, Mouse Magic (Peppermint and Spearmint based), Fresh Cab (Balsam Fir oil-based), TomCat Rodent Repellent Spray (Peppermint, Cinnamon, and Garlic oil-based)
2. ultrasound and flashing LED light rodent repellent device under the hood Loraffe Under Hood Rodent Repeller
   
3. parking car ~50' away on a different location than where the car was usually parked
4. glue trap set inside of the garage where the infestation must have started (caught a few mice so far) still seeing mouse activities in the car
   
5. blight LED light in the hood at night. Still, there are plenty of dark nooks and crannies they can hide.
6. keeping the hood open during the day in sunlight
7. oh, additionally, we have plenty of feral cats roaming around my property. My DW does the feral cats rescue by TNR. The presence of cats is no longer scaring the mice away. My car is parked outside on our driveway. The only way to get to it is to cross the blacktop driveway most likely from the nearby garage, where the infestation likely has been started. I have confirmed that the mice living in the garage are the deer mouse (Peromyscus maniculatus), not the house mouse (Mus musculus). Since their native habitats are the forested area, we basically live amid their natural habitat. Thus irradicating the population is not feasible. The best management is most likely to prevent them from entering and starting the nesting activities in locations I don't want them.

I have mothballs and dryer sheets to test next. I also ordered the capsaicin-infused rodent repellent tape.
Genuine Honda Rodent Tape - 4019-231

If all fails, my next step is to try this rodent barrier fence.

BoxKat Rodent & Mouse Barriers

But for now, I am just doing a vigilant daily check of mouse activities to make sure that they are not causing more serious damages

 

Funny that you mentioned CRC 06026 because that was exactly what I used for rust-proofing my PP. It was applied before the winter, and again after the winter at the time of tire changes. Granted, I did not spray it on the entire underbody with all the plastic covers removed nor in the engine bay, but I sprayed all exposed metal surfaces in the wheel well, suspension, and any frames and underbody parts I can reach.


When I was looking for repellent spray after discovering nesting activity in the engine bay of my PP ~10 days ago, I had a choice of picking either the one you mentioned by "Exterminator's Choice" or one by "TomCat"

The Exterminator Choice you mentioned has the active ingredients of Peppermint oil 0.32% and Rosemary oil 0.21% listed. The rest are water. The TomCat repellent which was suggested by someone on PC lists Sodium Lauryl Sulfate (1.500%), Peppermint Oil (0.500%), Cinnamon Oil (0.250%), Garlic Oil (0.002%) as active ingredients. As far as I am concerned they are basically the same stuff. I picked less expensive and more concentrated (Peppermint 0.32% in Exterminator Choice vs 0.50% in TomCat).



But so far, neither of them had much deterrent effect on repelling the mice who have invaded my PP's engine bay. After reading up on much of what is known on Peromyscus maniculatus (the scientific name for deer mouse) IPM (integrated pest management), I am now less convinced of the effectiveness of the "repellents" such as peppermint, herbal extracts, or hot pepper and the "frightening devices" such as ultrasound devices, blight lights, or loud noises. In general, they do not work to control and manage mouse activities.

Most scientific literature I have read so far are pointing to using the triad of IPM (integrated pest management).

1. exclusion (by a physical barrier)
2. habitat modification (making it less attractive to live by cleaning and not storing food or nesting materials)
3. population reduction (by rodenticide or traps)

Here is a good reading on that subject: Deer Mouse Management Guidelines--UC IPM

Only one repellent mentioned in some papers I have read that has been shown to be somewhat effective in repelling mice is Naphthalene (moss balls) in high concentration in a confined area. I have not given it a try. I can't use the moss ball in the cabin, but in the engine bay, I think I can place them in various locations without causing harmful effects to drivers and passengers in the cabin.

I will report my result after the trial.

 

As I said, there is no scientific backing on any repellents being effective in modifying mouse behaviors. The use of such agents and their effectiveness in deterring mice are almost all anecdotal and testimonial. If I find even a single real data on its effectiveness, I will have a little more confidence in the products, but at this point, IMHO, they are almost as good as "snake oil".

 

Yeah, if anecdotal testimony is proof, I am sure there are more automobile owners in the US who have done nothing to their car and have never had mice problems. That would suggest doing nothing works. I was one of them just until 10 days ago. LOL

Yep, it's on order. It is not smell-based like the peppermint spray, and apparently, they do work to prevent them from chewing the soy-based wires. But wrapping every wire harness would be impossible at this point. So I have some reservations about using the tape, it may just make mice go deeper in nooks and crannies where the tape is not applied and chew them there.

 

You are probably correct. I am sure that some repellents and deterrents do make the car less appealing to mice that are already well under control. So as a preventative measure, it may not be a bad idea. However, I will not likely be spending $35/gal on peppermint spray repellent which is more of a deodorizer than anything else. I already bought one bottle, so I will keep using it occasionally, but when the current bottle is gone that will be the end of that experiment.

As far as rust proofing... yeah, that's a different topic. If it works to prevent rusting and prevent mice from entering the engine bay, then I should treat my car. But chances are that with or without it, my car is not going to last 15 years in my region anyway. So, again it is probably not much benefit...

 

Thanks for answering my question. With all the orange cable going into it I thought it was an inverter, but I did not know for sure. I looked for the part diagram showing where the nest was found. But the part diagram shows only the inverter and not the associated parts. It is a silver metal pan that supports the inverter. I have no idea what the part is called. But it has a nice concave bowl-like shape and sit directly below the inverter, a perfect place for a mouse to hide and build a nest.

 

Nop. As I stated in my opening comment

We have plenty of feral cats roaming freely around our yard including directly around my car. In fact, there are scientific studies done on the effect of cats and dogs on the management of the mouse population, and it found that predators like cats do not have a major effect in curtailing the mouse population.

 

It may be. From the link, I found this diagram. I am not exactly sure which part it is and how it is attached to the inverter, but the shape looks like the right side of the diagram.

 

Population control is one of the triads of IPM along with exclusion and habitat modification suggested by many experts. The problem is that we basically live amid their natural habitat, the forest. I believe there are no mice living in the car right now. So setting a trap in or near the car would only attract new mice to the car. Moving the car and parking it ~50' away from the garage did not stop the mice from coming back to the car. Right now I have the trap set in the garage, but so far, only 5 mice have been trapped. No new mice were trapped in the last 5 days. If they are not coming from the garage, then I really don't know where they are coming from. It may be just coming from the forest behind our house... Then there is no way I can reduce the total population of mice in that vast area of natural forest... ~12 acres are mine but it abuts more empty forested lands belonging to others.