Rodents are mammals characterized by a single, continuously growing pair of incisors in both the upper and lower jaws. Their name, derived from the Latin rodere (to gnaw), reflects their feeding behavior, which significantly impacts plant life. The vast majority of rodent species rely heavily on plant material, making them overwhelmingly herbivorous or omnivorous. Spanning nearly every terrestrial environment worldwide, these gnawing mammals exert considerable pressure on natural ecosystems and cultivated crops, often causing significant damage as they feed and wear down their teeth.
Common Rodent Species That Consume Plants
Four main groups of rodents are most frequently responsible for plant feeding damage encountered in gardens, fields, and homes. Voles, often called meadow mice, are small, stocky rodents that primarily operate at or just below the soil surface, creating shallow runways and damaging plants near the ground. Squirrels, including both arboreal tree squirrels and fossorial ground squirrels, are highly visible culprits, with their activity ranging from the tops of trees to complex underground burrow systems.
House mice and rats, such as the Norway rat and the roof rat, are highly adaptable species that thrive near human habitation. Mice are generally smaller and consume seeds and seedlings, while rats are larger and inflict more extensive damage to sturdier plant structures. The diverse habits of these four groups mean that damage can occur across all seasons and at all heights, from underground roots to the highest tree branches.
Specific Plant Components Targeted for Feeding
Rodents target specific plant parts based on their nutritional needs, which often change seasonally. A primary target is underground components, including roots, tubers, and bulbs, which are rich in stored carbohydrates and moisture. Voles and pocket gophers often tunnel directly to these structures, feeding heavily on items like flower bulbs and the roots of young trees and shrubs. This subterranean feeding can sever the plant’s connection to its root system, leading to sudden wilting and collapse.
Rodents also consume structural components of plants, such as bark, stems, and the inner cambium layer. This feeding is often observed during winter when other food sources are scarce, as the cambium (the layer just beneath the bark) provides concentrated nutrients and moisture. When an animal chews a complete ring around a tree trunk, it causes damage known as girdling, which interrupts the flow of water and nutrients and can kill the plant above the wound.
The reproductive components of plants—seeds, nuts, fruits, and flowers—are highly sought after due to their dense energy content. Seeds, in particular, are a preferred food item for species like mice and many squirrels, who actively forage for them on the ground or directly from the plant. This focus on reproductive parts means that rodents can significantly affect plant populations by consuming seeds before they can germinate or by removing fruits before they ripen.
Recognizable Signs of Rodent Feeding Damage
The most definitive physical evidence of rodent feeding is the presence of characteristic gnawing marks left by their sharp incisors. These marks appear as parallel grooves on wood, bark, or hard fruit surfaces, distinguishing rodent damage from the irregular chew marks of insects or the tearing action of larger mammals. The width of these grooves can sometimes help identify the culprit, with smaller rodents like mice and voles leaving marks around one to two millimeters wide, while larger rats create wider marks, often three to four millimeters across.
Another telltale sign is the clean clipping of small stems, seedlings, and grasses, typically observed at ground level. Voles and mice use their sharp incisors to make a precise, angled cut, which looks distinctively different from the ragged edges left by slugs or the uneven browsing of deer. Often, only the upper part of the plant is clipped and then carried away, leaving a short, neatly cut stub.
Subsurface activity and tunneling also indicate the presence of rodents that consume plants from below. Voles leave visible, shallow runways in the grass or just under the soil surface, while gophers and ground squirrels create more substantial burrows, sometimes causing plants to appear loose or tipped over due to root damage.
Finally, the scatter feeding and caching behavior of some species, particularly squirrels, leaves behind evidence such as partially eaten nuts, dug-up bulbs, or scattered fruit fragments near the feeding site.