Voles are small rodents that grow to 3–9 in (7.6–22.9 cm), depending on the species. Females can have five to ten litters per year. Gestation lasts for three weeks and the young voles reach sexual maturity in a month. As a result of this biological exponential growth, vole populations can grow very large within a short time. A mating pair can birth a hundred more voles in a year. Voles outwardly resemble several other small animals. Moles, gophers, mice, rats and even shrews have similar characteristics and behavioral tendencies. Voles thrive on small plants yet, like shrews, they will eat dead animals and, like mice or rats, they can live on almost any nut or fruit. In addition, voles target plants more than most other small animals, making their presence evident. Voles readily girdle small trees and ground cover much like a porcupine. This girdling can easily kill young plants and is not healthy for trees or other shrubs. Voles often eat succulent root systems and burrow under plants or ground cover and eat away until the plant is dead. Bulbs in the ground are another favorite target for voles their excellent burrowing and tunnelling skills give them access to sensitive areas without clear or early warning. The presence of large numbers of voles is often only identifiable after they have destroyed a number of plants. However, like other burrowing rodents, they also play beneficial roles, including dispersing nutrients throughout the upper soil layers.