Rats are prolific chewers, and the question of whether they consume plastic or simply chew through it is a common concern for homeowners. Their destructive tendency causes damage to a surprising variety of materials, including wood, masonry, and various forms of plastic. Understanding the motivation behind this action helps explain why rats damage materials that hold no nutritional value.
Gnawing Instinct vs. Nutritional Consumption
Rats chew on plastic due to a biological necessity to wear down their continuously growing incisor teeth, not for caloric intake. These four front teeth are rootless and grow throughout the animal’s life, sometimes up to 1 millimeter per day. If this growth is unopposed, the teeth would become so long they could prevent the animal from closing its mouth, leading to starvation.
Gnawing is a survival mechanism that keeps the incisors filed to a functional length. The incisors have a specialized structure, featuring a hard enamel layer on the front and softer dentin on the back. When the rat gnaws on a hard surface, the softer dentin wears away faster, which naturally maintains a sharp, chisel-like edge.
When a rat chews through an obstacle like plastic, the goal is either to reduce tooth length or to create a path to food or nesting materials. Rats have a specialized anatomical feature called a diastema, a gap between their incisors and molars. Folds of skin extend into this gap, separating the front gnawing apparatus from the rest of the mouth cavity. This mechanism allows the rat to push plastic shavings and debris out of its mouth without swallowing them, confirming the material is discarded, not consumed.
Characteristics That Make Plastic Vulnerable
Damage to plastic materials occurs because their physical properties fall below the necessary hardness threshold to resist a rat’s powerful jaw. Rat incisors rank approximately 5.5 on the Mohs hardness scale, which is harder than iron or copper, meaning many common plastics offer little resistance. The susceptibility of plastic is determined by its gauge thickness and density, making thinner, softer, and more flexible materials the easiest targets.
Soft polyethylene (PE) used for water tubing or food storage bags is particularly vulnerable because it provides little opposition to the cutting action of the incisors. Plastic insulation surrounding electrical wiring is also frequently targeted. This poses a significant fire hazard when the protective coating is removed and copper conductors are exposed.
Rats may target plastic items as obstacles that need to be removed or as potential sources of nesting material, such as shredding plastic foam insulation. The texture of a material also plays a role, as the surface must provide sufficient grip for the rat to brace its bite and effectively file its teeth.
Health Risks from Non-Food Ingestion
Although rats rarely ingest plastic intentionally, accidental ingestion can pose serious health risks due to mechanical and chemical consequences. Small fragments or shavings that are swallowed are indigestible and pass through the digestive system as foreign matter. However, larger or sharp pieces of plastic, especially from hard containers, can cause internal trauma.
The mechanical dangers include gastrointestinal blockage, which prevents the passage of food and can lead to severe illness. Sharp fragments also risk perforation, causing tears in the lining of the stomach or intestines. Beyond mechanical injury, plastics contain chemical additives like plasticizers and flame retardants, which can leach into the rat’s system upon ingestion.
Studies involving laboratory rats exposed to microplastic particles show that even small fragments of materials like polyvinyl chloride (PVC) negatively impact physiology. Ingestion affects feed efficiency and causes changes in intestinal permeability. Research indicates that the chemical components and physical properties of plastic can disrupt the rat’s internal biological functions.
Material Resistance to Rat Gnawing
Preventing rat damage involves utilizing materials whose physical properties exceed the animal’s gnawing capabilities. The most effective materials are those significantly harder than the rat’s incisors. Hard metals, such as hardened steel and certain metal alloys, are the most reliable deterrents and are virtually impossible for a rat to penetrate.
Wire mesh or steel wool, when tightly packed into openings, effectively prevents entry because the abrasive texture resists gnawing. Solid, well-cured concrete and stone foundations are also impenetrable barriers, though rats can exploit cracks.
Specialized high-density plastics, such as high-density polyethylene (HDPE) or polypropylene (PP), offer increased resistance. These plastics can incorporate anti-rodent additives that generate an unpleasant taste or odor. Successful exclusion relies on the hardness and physical thickness of materials to resist the powerful, persistent force a rat exerts.