Gnawed furniture and chewed-up books are one sign. Tiny pellets and puddles of urine are another. A mice infestation can result in many other, more dire, results. Chewing through cords and wiring causes electrical fires, mouse allergens in the air lead to asthma, and feces and urine found in the cooking area contain pathogens that lead to food poisoning. Although traps and poison are a means to limiting rodent infestation, several natural-growing plants exist that, when ingested, will kill mice.
Avocado leaves and dried seeds kill mice. The toxicity level of the avocado varies depending on the variety of the fruit as well as the time of the year. Cases of rodent poisoning from avocados occur largely in southern California and Florida where avocado farming is rife.
Also called Conium maculatum, poison hemlock is an herb found throughout North America. The plant has fern-like leaves and clusters of small, white flowers that look like umbrellas. Hemlock contains a toxin called coniine, an alkaloid which causes depression, muscle weakness, respiratory failure, paralysis, and death. Any part of the plant containing a yellow, oily sap is poisonous, according to the Nova Scotia Museum. Poison hemlock leaves are especially toxic.
Solanum dulcamara, more commonly known as climbing nightshade or bittersweet, is a weedy vine found throughout North America, Europe, and Asia. Although the plant is related to the potato, its leaves and berries contain an alkaloid which is poisonous when ingested. Climbing shade produces berries which, while still green and not fully ripe, are lethal to mice. However, once the berries have matured and become red, they are no longer a fatal supplement to a rodent's diet.
Native to Madagascar, Kalanchoe daigremontiana—or Devil's backbone—has been introduced to Canada and parts of the U.S. (Florida, Puerto Rico, and Hawaii). Tiny buds growing along the edge of the plant's leaves frequently fall and litter the ground around its base. Devil's backbone contains a cardiac glycoside (a drug used to treat heart failure) that causes death in mice.
Monstera deliciosa, or the Swiss-cheese plant, is a popular "container plant" in households due to its ability to withstand a wide variety of conditions. In studies, rats and mice died after the rodents digested extracts taken from the plant.