Mouse Control: The best types of mouse traps and which ones to avoid
The Necessity of Pest Elimination
Mice are small, slender rodents that occupy a variety of habitats. Compared to rats and other rodents, mice easily adapt to novel situations and objects (Mice: Biology). Mice have poor eyesight, and must rely heavily on their other senses to experience their surroundings. While they will drink water when it is available, mice get most of their hydration from the foods they eat.
Mice as disease-carrying pests
They are natural omnivores and scavengers, and their regular diet in the wild consists of seeds, roots, leaves and stems, beetle larvae, caterpillars, cockroaches, and carrion (Mice: Biology). Mice prefer to eat foods that are high in fat, protein, and sugar, and tend to like many human foods. Mice live in open fields and forests, as well as in and around homes, agricultural land, and commercial areas, and are therefore considered to be a pest species (Timm, R.M House Mouse, 1981).
Pest elimination is something that many people consider to be necessary. Mice in particular cause problems in homes and businesses, and their extermination becomes crucial in order for humans to maintain their lifestyles and livelihoods. A large problem caused by mice is the contamination of food supplies with urine and feces (Humane Society) that can carry a wide variety of diseases transmittable to humans, including Hantavirus and Salmonellosis (Mice Problems).
The role of the mousetrap
The market provides a multitude of traps designed to alleviate this problem and effectively exterminate mice. These traps fall into two categories: welfare-friendly traps and traps that cause the mice to experience compromised welfare. Welfare-friendly traps include catch and release traps, while traps that compromise mice welfare include snap traps, glue traps, electric traps, and poison traps. Our aim is to design an effective extermination service through use of a catch and release mouse trap, and to ensure the welfare of the trapped mice while they are waiting to be released.
Mouse Traps and Animal Welfare
Set Point Analysis
There are several methods for determining animal welfare. One approach is through "set point" analysis, which involves the evaluation of an animals' overall health, including physical and behavioral aspects, as well as measurements of productivity determined through growth rate and reproductive performance (Lee, Y.S September 28, 2007).
Telos and Feelings Analysis
Other approaches include "telos", determined through evaluation of an animals' behavior, and "feelings" which is determined by evaluating both behavior and by designing experiments to test animal preferences (Lee, Y.S. September 28, 2007).
Scientific Analysis: the Five Freedoms
Animal welfare cannot be properly determined through approaches that lack scientific methodology, such as applying the concept of anthropomorphism or the belief that if an animal appears to be happy or is in a situation that a person himself would be comfortable in, that the animal must be comfortable in that situation as well. This approach is fallible as behaviors of nonhuman animals can be very different from human behaviors, and what we interpret as content behaviors may actually be forms of stereotypy that result from stress.
Ideally, welfare-friendly traps should maintain animal health physically and emotionally, and have no detrimental effects on performance while allowing animals to perform "normal behaviors" they are highly motivated to perform, as determined through close observation and experimentation.
These normal behaviors welfare-friendly environments must allow are outlined by the Animal Welfare Council. According to this council, animals should be allowed the following five freedoms: "Freedom from thirst, hunger and malnutrition; freedom from thermal and physical stress; freedom from injury and disease; freedom to express most normal behavior of the species; and freedom from fear" (Animal Welfare Council 1993). A great number of common mouse traps used today deny mice these basic freedoms.
Can a Mouse Feel Pain?
The 8 requirements
In order to properly evaluate if certain traps cause compromised welfare in mice, it must be first determined whether or not mice experience pain. According to the eight requirements listed by Bateson, for organisms to feel pain they require the following: "nociceptors in functionally appropriate places, nociceptors connected to lower parts of the CNS, a higher brain center, pathways that are traceable from the nociceptors to the higher brain center, neurotransmitters analogous to substance P and opiods, a pain response that is functional, a pain response that is modified by analgesia, and to learn not to repeat" (Bateson 1991).
These requirements appear to be mostly met through data accumulated in a study by Yan-Gang Sun and Zhou-Feng Chen in which afferent nociceptors were tested in mice to determine substance P release levels. Nociceptors were aggravated through thermal, mechanical, inflammatory, and neuropathic agents and elicited pain responses in mice, such as paw withdrawal from hot plates and paw licking upon injections causing inflammatory responses, were then measured and recorded (Sun, Y.G, Chen Z.F 1997).
The spinal cord of mice was also used for immunocytochemistry data, and while preparing the spinal cord for study the mice were "deeply anesthetized" with sodium pentobarbital (Sun, Y.G, Chen Z.F 1997). Furthermore, levels of hyperalgesia, or increased sensitivity to pain, were measured in mice, related to the presence of substance P (Sun, Y.G, Chen Z.F 1997). Therefore, this study indicates the presence of nociceptors, a spinal cord, neurotransmitters similar to substance P, and a functional pain response which is modified by analgesia.
A Mouse Trap Comparison
5 common types
With the knowledge that mice can experience pain, mice traps can now be properly assessed for their welfare potential. Some common mouse traps include the baited snap trap, catch and release style traps, glue trap, electric trap, and poison trap, in order of their popularity in local hardware stores (AceHardWare.com).
The Snap Trap
A snap trap ideally functions by luring a mouse across the trap from one side to the other to get to the bait on the other end. On its journey, it triggers a spring which causes a metal bar to snap up and break the mouse's back, killing it instantly. In reality, this does not always happen.
It is not uncommon for a foot or a tail to get caught in a snap trap, and for the mouse to gnaw itself free while leaving the trapped appendage behind-the mouse must be under physical and mental stress if the pain of being stuck in the trap is greater than the pain of chewing off a limb. If the mouse remains in the trap but is not killed or removed, it will most likely starve. Its injuries alone probably cause the mouse to experience a great deal of stress, and immobility and starvation only add to the mouse's suffering.
Mice in this situation have compromised welfare according to "set point" analysis, as the health of the animal may easily be jeopardized by a broken bone or limb as well as impaired access to nutrition and hydration, accompanied by a stressful situation in which the normally hyperactive mouse is immobilized. Due to this immobilization, almost all normal behaviors of the mouse are inhibited, and since self-mutilation of a paw or tail is abnormal, by "telos" and "feelings" standards the mouse in a malfunctioning snap trap experiences compromised welfare by displaying abnormal and pain inducing behaviors which it would not otherwise display.
In relation to the new five freedoms outlined by the Animal Welfare Council, mice caught in snap traps are denied every freedom. They are unable to have ready access to food or water, cannot escape trapped environments at unfavorable temperatures, cannot escape the stress inducing situation in which they are placed, have most likely amassed physical injuries upon the trap's malfunctioning as well as their own attempts to free themselves. Furthermore, they cannot in any way satisfy their highly motivated natural behaviors, and cannot escape the trap although it most likely inspires great fear and distress.
The Glue Trap
Glue traps cause similar welfare compromising conditions for mice. While glue traps are not meant to kill the mouse or break any bones, they are just as stressful and painful as the snap trap for many reasons.
Firstly, the mouse may manage to have only one leg or a tail stuck to the glue tray, and it will likely gnaw this appendage off to free itself. Secondly, the mouse's entire body may be stuck to the trap. In this case, the stress from being completely immobilized and the exhaustion from struggling and having no access to food or water for extended periods of time can be tremendously uncomfortable.
According to the "set point" evaluation, mice stuck in glue traps experience compromised welfare because of the lack of access to nutrition or hydration, an inability to regulate homeostasis through movement or nutrient intake, an impaired ability to grow and reproduce, and their behavior that threatens internal balance such as self mutilation. According to "telos" evaluation, the mice fall short of acceptable welfare as they are immobilized and unable to perform their species specific highly motivated behaviors, and if their entire bodies are stuck to the trap they are incapable of any movement at all. By "feelings" evaluation, if mice will chew off a limb or tail to free them from the situation there must be strong negative feelings associated with that situation and as long as they remain trapped their welfare is compromised.
The Electric Trap
An example of an electric trap, the Rat Zapper, is designed to kill mice instantly through electric shock. The Rat Zapper is a small box with one opening and bait at its end. Once a mouse steps into the box to retrieve the bait, it is electrocuted by receiving a deadly shock, after which a light will blink to alert the trapper that a rodent has been caught.
However, this trap is battery operated, and it is possible that in between battery changes the power will initially diminish and then run out, and according to a customer complaint on amazon.com, alkaline batteries sometimes only last long enough to kill one or two rodents (http://www.amazon.com/Rat-Zapper-Mice-Trap/dp/B0001LE2DY).
If a mouse enters the trap in between battery changes it could be zapped at strength insufficient to result in its death yet great enough to bring about physical or mental distress depending on its voltage.
In accordance with "set point" evaluation, welfare has not been met, as instead of maintaining homeostasis, the animal's electrocution causes a great disturbance in body processes. If the nonlethal shock is strong enough, lasting physical and mental abnormalities could occur, disabling normal body and brain function in the mouse. By "telos" evaluation, an animal impaired through nonlethal shock would be incapable of performing all normal behaviors with limited movement and mental processing. "Feelings" evaluation would most likely result in animals having strongly negative feelings towards physical impairment.
Measuring partially zapped mice by the five new freedoms, the degree to which a partial shock affects them is important regarding the extent of this trapping method's effect on the mouse's welfare. If the shock is of a great enough magnitude, all five freedoms could be effected as the mouse could be unable to realize its need for food and water, proper thermal conditions, to express normal behavior of species, or may be unable to move around properly in order to meet these needs. The mouse could have sustained injuries through the impartial electrocution, and it is possible its handicapped state can cause the mouse stress and fear.
The Poison Trap
Poison is a very commonly used method of extermination; unfortunately, it is not welfare-friendly. The types of poisons used cause the mice to bleed to death internally.
Symptoms preceding death depend on the type of poison used--acute rodenticides can cause symptoms such as "nausea, vomiting, and pulmonary edema" before the mouse dies, and some forms of anticoagulant rodenticides can cause "symptoms of injury" before fatal internal hemorrhaging takes place (Solymar, B. Rodent Management 2001).
By ‘set point' analysis, the animals' welfare is not met as uncontrolled internal bleeding prevents proper body function. By ‘telos' analysis, when the animals have lost sufficient levels of blood, they will not be able to perform all normal behaviors due to weakened physiology and sickness. ‘Feelings' analysis would also point to compromised welfare, as stomach upset, physical weakness, symptoms of injury, and internal hemorrhaging would most likely inspire negative feelings in mice as they are linked to sensations of pain, which mice have been shown capable of experiencing.
The five new freedoms are all denied poisoned mice. Hemorrhaging, vomiting, and symptoms of injury can cause malnutrition in mice, as well as great amounts of physical stress and internal injury. Under these conditions mice can readily experience fear and cannot easily perform species specific behaviors.
The Catch and Release Trap
Fortunately, there are alternatives to the grisly traps that kill mice in stressful, welfare compromising ways. One such alternative is the catch and release method, the second most common trap, in which a mouse is caught and released back into the wild.
The "No Kill" Smart Mousetrap is an example of a catch and release trap. The Smart Mousetrap consists of a plastic box that a mouse will enter in search of food. A spring-loaded door closes behind the mouse, trapping it until it is released. Once the mouse is found, it is easy to release it-simply go to a remote area and pull up a door on the end of the trap, revealing a cracker slot. The mouse can chew through the cracker and exit the trap on its own time, thus eliminating the stress that it would endure if it were simply dumped out of the box and into a new environment.
The best trap by far, which we will call the Trap Well trap, although similar in concept to the Smart Mousetrap, will also have many necessary alterations proved by scientific research to be necessary for optimal mouse welfare. This trap does not exist on the market, but for all the reasons enumerated below, it should.
Keeping Mice Stress-free
Laboratory mice require the ability to rest, groom, explore, hide, forage, and gnaw, in addition to nutrition and sanitation, all which are considered "innate" characteristics they have in common with wild species of mice (Bauman ILAR JOURNAL Vol 46, Number 2). Environments preventing the performance of these behaviors may result in the performance of stereotypies (Van de Weerd), indicators of compromised welfare according to the ‘telos' evaluation of welfare.
Enriched environments allow mice to readily perform natural species specific behaviors, and an example of appropriate enrichment involves enlarging small cages (Van de Weerd). According to the UC Davis Environmental Health and Safety Committee Policies and Guidelines, a single adult mouse should be housed in an enclosure of at least 15 square inches (UCDavis). Therefore, because it is smaller than 15 square inches and only allows for 10.5 square inches of space, the Smart Mouse trap, or any other trap smaller than our Trap Well trap, can cause overcrowding.
In an overcrowded situation the mice may have insufficient room to explore, hide, groom, or rest, which are innate species specific behaviors. In addition, too small of an enclosure may hinder the animal's ability to apportion their environment into distinct areas for food, rest, and defecation, and therefore cause it to feel little control over its environment, increasing it levels of stress (Brumans ILAR Journal Vol 46, Number 2), and thereby violating many of the Five Freedoms.
Another method mice use to reduce stress and feel in control of their surroundings is manipulation of nesting material, which may "enhance their well-being" (Van de Weerd). Through studies performed by Heleen Weerd, PhD and Vera Baumans, PhD, preference testing showed that mice valued nesting material more than nesting boxes, and would even use nesting material covering wire flooring that they usually have strong preferences against (Van de Weerd).
Furthermore, mice given bedding, when compared to mice that were not, weighed more although they ate less (Van de Weerd). This suggests that nesting materials either aided their ability to regulate their internal body temperature or offered them a sense of security and lowered their stress levels in general compared to the mice that had no nesting materials (Van de Weerd). Nesting behavior is an innate behavior that mice are highly motivated to perform, shown by the above study in which all mice used nesting material when it was available.
Therefore by ‘telos' evaluation, mice experience improved welfare when provided with nesting materials. According to ‘set point' and ‘feelings' evaluations, mice experience improved welfare as well, as nesting materials helped maintain homeostasis through body temperature regulation and the animals had strong feelings of preference for the nesting materials.
Mice can hear ranges of sound from 80 Hz to 100kHz, with heightened sensitivity at ranges from 15kHz to 20kHz and at 50kHz as well (Sherwin, C.M.). Mice are more sensitive than humans to loud and sudden noises, and chronic noise can cause decreased activity and fertility, instability in blood glucose and corticosteroid levels, as well as seizures and convulsions (Sherwin, C,M).
For this reason, it is important to use a method of alerting the mouse's presence in the Catch Well trap that makes little or no noise, such as a flickering light triggered by a sensor, similar to that of the Rat Zapper. Notice of the mouse's presence in the trap as soon as possible is crucial to its welfare, as the trap is designed to support mice for 24 hour time intervals, and mice trapped in it for extended periods of time may suffer from deprivation of food and water and unsanitary conditions.
The artificial lighting that lab mice are exposed to, similar to the artificial lighting of homes and businesses, is brighter than their natural environment and can lead to eye abnormalities such as retinal atrophy (Sherwin, C.M). Therefore, to better protect their eyes from their surroundings, the Trap Well trap will be made of a dark colored plastic, to prevent the full intensity of surrounding light from penetrating the trap. Although mice have been found to form retinal atrophy after 12 months of exposure or longer (Greenman et al. 1982), the fact that bright lighting can cause such ultimate deterioration of the eyes suggests that exposure to bright lights, if only for minimal amounts of time, may also cause discomfort to the animal.
As far as lasting affects, exposure for 24 hours has not been proven to cause irreversible damage; however, due to the nocturnal nature of mice and their avoidance of light in general, in addition to the development of retinal atrophy within a year of bright light exposure, suggests that mice are highly behaviorally motivated to avoid such conditions and may even experience pain-the body's natural mechanism for avoiding destruction of tissues, such as the retina.
This is further supported by the introductory paragraph in a study by Michel Bourin and Martine Hascoet on light/dark box testing of mice, in which it is stated: "the light/dark test is based on the innate aversion of rodents to bright illuminated areas and on the spontaneous exploratory behavior of rodents in response to mild stressors, that is, [...] light"(Bourin, M. Hascoet, M. 2002). Caught in a trap in an artificially illuminated home or business could therefore cause mice stress due to their inability to practice the species specific motivated behavior of seeking darkness; therefore, with dark plastic our Trap Well trap will create a more natural environment for the caught mice and protect their eyes from damage.
Our Trap Well trap will also have solid flooring to eliminate any discomfort mice could experience from floors constructed of mesh or wire. Over time such floors can result in pressure sores (Sherwin, C.M); although, these take longer than 24 hours to develop.
However, mice show a natural tendency to avoid mesh and wire flooring when offered other options during preference testing(Sherwin, C.M), which proves that such floors offer less comfort even for minimal periods of time. Therefore, to offer maximal comfort to mice, in accordance with "feelings" evaluation of proper welfare, the Trap Well trap will offer them flooring materials for which they have shown a strong preference, and which is known to have fewer potential health risks to the mice's feet.
**disclaimer: the Trap Well trap does not in fact exist, but it should! Catch and release traps in general are superior over all other kinds, and bringing caught mice to a local veterinarian for quick euthanasia is desirable over all other options short of making the pest a household pet. Most veterinarians will do so free of charge. Releasing the mouse into a field is also a possibility, but if not far enough away it may return or if not will likely become a victim of the circle of life. There is no easy solution, only better ones, in working to solve an enduring problem.