Dealing with Rodents in the Home

By Brian Tomasik

First published: . Last nontrivial update: .

Summary

This page collects some information I've found about dealing with home rodent infestations, as well as stranded baby rodents. I'm not an expert on these topics, but hopefully the linked resources will be helpful. As always, prevention is the best long-term solution when possible.

If you must kill mice in your house, my best guess is that alphachloralose is among the least painful ways of doing so. Snap traps also seem less bad than most other options.

While I haven't investigated it much yet, you may want to look into the SenesTech "fertility control bait" called ContraPest, which seems like the most humane method of all, although it "must be deployed by a licensed Pest Management Professional."

Note: The best information on rodent-control methods I've seen is UFAW (2008): "Guiding principles in the Humane Control of Rats and Mice". In fact, that document is better than my own piece.

Contents

Dealing with rodents in the home

Prevention

Rattus norvegicusIt's most important to prevent rodent problems from getting started in the first place. For tips, see PETA's "Living in Harmony with House Mice and Rats" and the Humane Society's "What to Do About Wild Rats".

In the long term, the most effective, and perhaps only, way to prevent a rodent problem is what's known as "exclusion"—keeping rodents out of the home to begin with, such as by sealing holes and other entry points. You could hire a pest-control company to help with this process.

Another obvious step is to avoid leaving food out. Doing this helps to prevent not just rodents but also ants, fruit flies, etc.

I also cover garbage cans and hang full garbage bags up off the floor to prevent rodents from getting inside. The worst case would be if a rodent was in a garbage bag when it was thrown into the garbage crusher at my local transfer station.

Coexistence

Many of the rodents in my home live mostly in the walls, where they don't cause trouble. The main problem is when they come out at night, e.g., into the kitchen. But if you don't leave food out—and instead put it in the fridge, in sealed cupboards, or high on unclimbable shelves—the rodents may not be a huge problem even if they do come out at night.

Traps

Unfortunately, my housemate insists on trying to kill the rodents in our house using traps.

Snap traps

When my housemate sets up snap traps, I check these traps regularly during times of the year when rodents are abundant, since I worry that a rodent might get trapped in a position that isn't immediately fatal. I think I've seen this happen in one or two cases, but probably at least ~90% of the time, these traps snap the rodent's neck and therefore kill relatively quickly.

In the typical case when a snap trap captures the head of a rodent, the trap seems to kill within a minute or so, but during that time, the rodent appears to be in extreme pain. Here are some videos of snap traps catching rodents:

I'm not sure how much the struggling movements are unconscious in these videos, but without knowing more, it seems prudent to assume a decent portion of the time before death involves conscious agony.

UFAW (2008), p. 7: "There is no requirement for traps to be tested for humaneness prior to being placed on the market and, as far as we are aware, no information is available on the humaneness of the various designs available. Mason and Littin (2003) reported evidence that between designs of snap traps used in the USA, the incidence of mis-captures by a leg or tail varied from 4 to 57%."

I've pondered whether there's a technological solution to reduce the burden of checking the traps to watch for trapped-but-not-fully-killed rodents. For instance, could I buy a motion detector of the type normally used as a burglar alarm? Could I buy a motion detector that hooks up to my computer? Both options seem like they might work, but I haven't gotten around to trying them.

Live-capture traps?

On Amazon, I came across "Southern Homewares Multi-Catch Clear Top Humane Repeater Mouse Trap", which seems to have good reviews. If you use it, you should check it a few times per day to reduce the length of time during which rodents are traumatized inside it, unable to escape. One reviewer notes that the trap can catch even without bait. Therefore, if you stop checking the trap regularly, you should put it away in a plastic bag or other sealed container, perhaps on top of a shelf, to avoid the risk of accidentally capturing a critter who will then die slowly in the trap.

I would guess that live-capture traps are pretty stressful for caught animals, since the animals don't know if they'll ever escape. In addition, you have to dispose of the animals somehow. If you drop them off near your house, they may come back inside. Meanwhile, as UFAW (2008) says (p. 5): "Release of an animal elsewhere is not necessarily a humane thing to do – translocated animals may fail to adapt to or integrate into new territory and may suffer and die as a result (Mason and Littin, 2003)." Finally, killing a live animal humanely is difficult, and there's a risk of getting bitten, which could transmit disease.

For these reasons, I suspect that snap traps may actually be more humane than most uses of live-capture traps.

Electric traps: NOT a good solution

When I searched for mousetraps on Amazon, one possibility that I found was to use electric rodent zappers. Some sources suggest that electricity might be less painful than other methods. According to HSUS: "the traditional snap trap, and perhaps the newer traps that use an electrical charge to stun and kill, seems to be the least inhumane."

However, I was taken aback by the fact that the electricity zap lasts for two minutes:

According to "Rat Traps":

Rats have the unusual ability to restart their hearts after minor electric shocks [...so] electronic devices must provide a longer term exposure to voltage to ensure a kill.

UFAW (2008) says (p. 10) of electric zappers:

The humaneness of these devices will depend upon whether sufficient current runs through the brain and for long enough to cause immediate loss of consciousness from which the animal will not recover prior to death. If this occurs then, based on studies of electrical stunning and killing of farmed animals, it is likely that the method is very humane; if not, and the animal remains conscious, the shock is likely to cause severe pain prior to the animal’s death from cardiac arrest (probably within 2 minutes). We are not aware of much information about the efficacy and humaneness of these devices.

An instance of a bad zap can be seen in the video "FrankenRat - Ultra Rat Zapper does NOT kill humanely. (Don't let kids watch this. It's sad.)" It shows a rat walking into an electric trap, struggling for about two minutes as it gets zapped, and then escaping. One person in the comments said: "Yeah, I think it's a defective model. Zappers are supposed to keep a steady shock for 2 minutes because a rat's heart can restart after the initial jolt. Poor thing looks to have suffered nerve damage." (Many of the other comments are not pleasant to read. Sometimes people's hatred of the damage and disease that rats cause spills over into apathy about or enjoyment of rat suffering. Maybe this is a misfiring of revenge impulses that make more sense in the human realm where vindictiveness may sometimes help prevent future antisocial behavior.)

Most rodenticides are NOT humane

UFAW (2008) discusses anticoagulant rodenticides (pp. 3-4):

Rats may show signs including weakness, lameness, and breathing difficulties, for up to about 48 hours prior to death (which in rats is typically about 3-9 days after ingesting a lethal dose). Bleeding into joint spaces and inside the skull is known to be very painful in humans and there is a concern that anticoagulants may cause this in rodents. For this reason the UK’s Pesticide Safety Directorate described this method as ‘markedly inhumane’ (Mason & Littin, 2003; MAFF, 1997).

UFAW (2008) also explains that cellulose pellets used to kill rodents are plausibly inhumane.

However, not all rodenticides should be discouraged; see the next section.

Alphachloralose

Alphachloralose can be used to kill mice indoors in perhaps a somewhat gentle way. Mason and Littin (2003) give an overview of the effectiveness and humaneness of this chemical (pp. 10-12). Alphachloralose can only be used when temperatures are below 15 to 16 degrees Celsius, and it can't be used for rats (p. 11).

As of 2019, alphachloralose is pending approval in the USA (Tomasko 2019), while it's already available for use in at least parts of Europe.

Based on what little I've read about alphachloralose, I find it plausible that it's the most humane way to kill mice in the home, with snap traps being a close second. The main risk I see comes from the fact that alphachloralose takes a lot longer to kill than snap traps do. Snap traps usually kill within ~10 seconds, while alphachloralose takes at least 15 minutes to induce unconsciousness. However, the intensity of pain per second is presumably vastly greater in the case of death by snap traps, and it's unclear whether there's any intense pain during death by alphachloralose.

What to do with abandoned baby rodents?

In Sep. 2014, I found two baby rodents in the middle of my kitchen, without a mother or nest in sight. They had their eyes closed and were motionless apart from breathing. It looked like these rodents would probably die if left alone. What are the options in a situation like this?

Professional euthanasia

The most humane way to euthanize rodents is to take them to a vet. One person on this thread reports taking two rats to a vet for euthanasia at a cost of $50 total. Another person on that thread says: "Don't do at-home euthanasia. Take him to a professional, this is still an innocent animal's life and if you screw up the euthanasia in some way, your rat will be in a lot of pain." Another site confirms that euthanasia of a small animal costs only $25. (EDIT in 2017: The price is now $45.)

This page reports a "euthanasia fee" of "$20.00 for bunnies and small critters".

This thread points out that different vets may euthanize small animals in different ways, some of which may be more painful than others. It's probably good to ask the vet how s/he plans to do the euthanasia.

Caring for them

Some sources suggest feeding and caring for helpless baby rodents that you may find. However, raising baby rodents requires a lot of effort:

If your orphan is a new born you will need to feed it every 1-2 hours as a minimum. You must do this around the clock. This will make for many sleepless nights and one of the reasons that taking care of orphan mice is so challenging.

Survival prospects are not great:

Orphans can be very difficult to hand raise, especially if they are less than a week old. The mortality rate of hand raised orphans is about 50% (Creek Valley Critters says about 75%).

Even if the rodents survive to adulthood, they'll still die potentially painful deaths at that point. Indeed, the adults are probably more sentient than the babies, so death would likely be more painful by then. According to "Guidelines for the Euthanasia of Rodent Fetuses and Neonates" (p. 1): "Maturation of nociceptors and the development of excitatory and inhibitory receptor systems occur during the period just prior to birth and into the second week of postnatal life."

Decapitation: Not recommended unless you can't do professional euthanasia

Rodent guillotines are used in labs, which suggests that decapitation, while awful, may be among the better ways for a rodent to die. If the rodent isn't moving, then decapitation could be done with a powerful cut of the neck with a strong pair of scissors. If you're worried about getting germs on the scissors, you can buy some extra pairs (such as these for $8 each) and throw them away after use. Before you throw out the scissors, I recommend putting them back into the plastic case they came in so that the pointy tip isn't exposed. This reduces the risk that they'll poke someone handling your trash. If you want, you could then put the scissors into a hard container in the trash to further reduce the risk of poking.

Although some articles suggest that the only AVMA-approved rodent-euthanasia method possible with home equipment is CO2, AVMA isn't completely opposed to decapitation either. Pages 38-39 of its 2013 guidelines explain that "Decapitation appears to induce rapid loss of consciousness". The listed downsides are that

  1. Handling and restraint may be stressful for the animal. This downside wouldn't apply to motionless baby rodents.
  2. Electrical brain signals persist for 13-14 seconds after decapitation. This is an important downside that I'll discuss more below.
  3. Guillotines may be dangerous to the humans using them.
  4. "Decapitation may be aesthetically displeasing to personnel performing or observing the method." But that's not a very good reason. If anything, killing should look unpleasant so that we don't take it lightly.

Persistence of brain signals after beheading is a concern. It's unclear whether the guillotine is humane for humans. For instance, although I don't know the veracity of these reports, they are troubling:

In France, in the days of the guillotine, some of the condemned were asked to blink their eyes if they were still conscious after the knife fell.

Reportedly, their heads blinked for up to 30 seconds after decapitation. How much of this was voluntary and how much due to reflex nerve action is speculation. Most nations with science sophisticated enough to determine this question have long since abandoned decapitation as a legal tool.

I've seen chickens continue to move for probably about 30 seconds after beheading, although again, it's not clear how much of this is due to lingering motor impulses after full-brain consciousness has been extinguished.

Further information:

Of course, we should probably prefer chemical euthanasia if this is possible.

I was curious whether people use scissors for decapitation, and I found one person on Ask MetaFilter who had:

when I worked in a lab, I cut the heads off mice with scissors. Works best with the bandage/crash scissors that you sometimes see cutting through a penny. Just pick the mouse up with a gloved hand and snip the head off behind the ears. Super fast. Always lethal. Our lab had a tiny murine gas chamber attached to a CO2 tank, but they die very slowly that way and look like they suffer.

Someone on Yahoo Answers feels similarly about CO2: "Don't do CO2, that is generally accepted as a form of euthanasia but can be incredibly painful if done incorrectly at home and can cause far too much stress."

CO2 may be particularly ineffective for baby rodents because "Resistance to hypoxia at this age results in a prolonged time to unconsciousness when CO2 is used as a euthanasia agent." The same document says (p. 2): "Mouse, Rat, and Hamster Neonates up to 10 days of age: Acceptable methods for euthanasia include: injection of chemical anesthetics (e.g., pentobarbital), decapitation, or cervical dislocation."

In Sep. 2017, I found a young rodent in my house that had unfortunately been cornered by my housemate's cat. I moved the cat away from her intended victim. Normally when I do this, it allows the rodent to escape, but this time, the rodent remained where it was. It was clear that the rodent could barely move, perhaps due to exhaustion or leg injury. It was late on Sunday night, with no vet offices open, and the rodent appeared terrified, so I figured that euthanizing it was the least bad option. I cut its head off with scissors (which wasn't hard to do because, as mentioned, the rodent could barely move). After decapitation, the rodent's mouth moved slightly open and shut for maybe 8 to 15 seconds? (I don't know exactly, since I didn't have a stopwatch.) I hope the rodent wasn't conscious during that whole time, but even if so, decapitation may still have been the best way for it to die under the circumstances.

Interestingly, decapitation can take much longer to stop brain activity in reptiles. Barten (1994/2014): "the brain of a decapitated reptile may remain active for up to an hour, so decapitation by itself is inhumane."

Leaving the rodents to die: Not a great option

Leaving rodents to die on their own probably isn't pleasant. I'm not sure how such rodents die, but possibilities include hypoglycemia, hypothermia, or dehydration?

Some terminally ill humans deliberately withhold food and water as a way to die. On the other hand, inhibitions against euthanasia seem to stem from religious and instinctive impulses that may contradict hedonic welfare. And modern medicine allows for pain relief; without it, I suspect the demand for euthanasia would be much higher.

That laboratories euthanize animals is weak evidence that euthanasia is more humane than leaving animals to die. On the other hand, maybe laboratories need to kill the animals quickly and don't want to wait for them to die on their own?

CO2 euthanasia: NOT recommended

In response to the Quora question "How do you kill (euthanize) a mouse your cat has brought in?", the top answer on Quora suggests to "put it in a jar and let it suffocate", based on the principle that CO2 is, "Of those methods for euthanasia approved by the American Veterinary Medical Association (AVMA), the only method that could be used safely at home". However, I'm nervous about this approach, since it seems like rodents would probably be quite distressed.a In addition:

  1. CO2 is generally not nearly as humane as certain other gases for euthanasia. This has been confirmed in the case of rats.
  2. Individuals at home may not have the materials to create a serious CO2 euthanasia device. This page recommends using vinegar and baking soda to create CO2 in one container that can then be fed into a second container via a tube. Other sources recommend the same. But you may not have such a tube on hand, and such a tube looks like it might be important for preventing the CO2 levels from rising too quickly. This page explains:

    In low concentrations (7.5%) [CO2] is an analgesic (pain reliever), and at medium concentrations (30%-40%) it can be used as an anesthetic, causing rapid loss of consciousness without struggling, distress, or excitation. Medium concentrations cause an aversion responce in some rodents[.] At high concentrations (>80%) CO2 causes quick death. High concentrations, however, painfully irritate eyes and the respiratory tract, so it is important to first induce an analgesic effect, then bring about deep anesthesia (within 1 to 2 minutes) before exposing the animal to high concentrations.

    Other people suggest creating a two-container chamber but without needing a hose, but this also seems daunting.

This source says:

I totally agree that this (euthanasia) is not the sort of thing you try until you've thought it through (morally and operationally) and practiced it without any living creature. While my personal position is that as pet owners we sometimes have an obligation to end life before the quality is diminished (I respect those who feel otherwise), that also means we must exercise informed judgment about this act AND must do so as 'cleanly' as possible (in other words, this is no time for 'amateur hour' where a mouse is exposed to insufficient or excessive levels of anything or the effort to end their suffering only serves to prolong it).

Sterilization

Rodent sterilization seems like a good way to control large numbers of rodents. In 2013, New York City tried sterilization and reduced rat populations by 43% in the tested areas (Swartz 2014). Sterilization doesn't poison the rats, making it relatively humane.

As of 2017, SenesTech has "a liquid fertility control bait for rodents" called ContraPest. "ContraPest received the fastest EPA approval in history at the time of its registration and has been approved for use in 49 states, awaiting approval in California. ContraPest must be deployed by a licensed Pest Management Professional."

Acknowledgments

Adrian Rorheim introduced me to some reading on alphachloralose.

Footnotes

  1. More discussion of this question from "Euthanasia – The Carbon Dioxide Debate":

    [Person 1:] I'd argue that just letting the CO2 build up naturally would be a very traumatic experience. Mice don't produce that much CO2 - it would take a very long time. In the meantime they'd produce a tremendous amount of moisture. Mice don't respond well to such enclosed spaces (panic or uncertainty) and they'd soon be wet from all the moisture, and you still wouldn't have reached a CO2 level sufficient enough to produce unconsciousness. Finally, the issue here isn't that there is no oxygen left in the tank (that truly would be suffocation). In such a state, the mouse would panic and hyperventilate (as it desperately sought oxygen). Instead, you want oxygen in the tank but also high levels of CO2, which produce unconsciousness and then brain cessation.

    [Person 2:] I don't think it's accurate to say that CO2 'suffocates' an animal (or a human for that matter). In fact, if there is sufficient oxygen in a room or chamber, CO2 produces an effect where part of the brain shuts down and unconsciousness results. Suffocation happens when there is no oxygen or we cut off someone's ability to breathe (such as choking). Typically, what happens with CO2 is that the mouse quickly loses consciousness and actually continues to breathe for up to a minute or more before breathing stops.

    If I can use an example to illustrate this, during the Apollo 13 mishap in space, at one point there was concern about excessive CO2 in the space capsule. There was sufficient oxygen for the astronauts but because the filters that removed the CO2 were saturated and the CO2 levels in the capsule were gradually building up. This would produce dulled thinking, slower reaction times and then unconsciousness and death (and this was at relatively low levels of CO2 over time). Low levels of oxygen produce headaches and hyperventilation (much like climbers at high altitudes experience). But placing CO2 in an enclosed chamber does not mean insufficient oxygen.

    During the 'orange' alert status here in the USA (fear of Al Quaeda attack), all of this talk about finding a 'safe' room and taping up vents, windows, etc. has led to the worry that if one were to do that, it might lead to death by CO2. In those instances, it would NOT be a case of someone breathing all the oxygen in the room up (because it's an enclosed space). Rather, it would be because the levels of CO2 would rise to dangerous levels. And we as humans wouldn't notice it. We would just get a little slower in our thinking, then fall asleep and (unless there was an escape for the CO2) ...die. Only at incredibly high levels of CO2 would we notice that there was anything out of the ordinary (those high levels would need to be near 100% from what I understand - and levels of 25% are supposed to be sufficient for humans to become unconscious and then die).

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