Beavers
Click for larger image A willow (Salix) gnawed more than halfway through by a beaver.

Weighing from 40 to 60 pounds and 3 to 4 feet in length from nose to tail, beavers are the largest rodent native to North America. Beavers occasionally come into conflict with humans when their dam and lodge building activity damages trees and floods cropland, roads and areas along streams or when they consume garden crops.

Symptoms and Diagnosis

The most obvious sign of beavers is the presence of a dam, lodge or food cache. These structures resemble a brush pile in the water. However, in areas where flooding is common or where the water level fluctuates, beavers dig dens in the bank of a stream or under the roots of a tree growing beside the water. Other signs of beaver include fallen or standing trees with gnaw marks, especially on the water side of the tree. Trees may be entirely or partially girdled. Mounds of mud, leaves and other debris that beavers use to mark their territory may also be present.

Life Cycle

Beavers are mainly nocturnal and semi-aquatic, although they will leave the water to cut trees and forage for food. In Missouri, they breed in February and the young, an average of 3 to 4 per litter, are born in late April or early May. Young beavers generally stay with the family group for 2 years. Beavers primarily consume the bark of young twigs and the new growth between wood and older bark. Many species of trees are eaten including cottonwood, willow, oak, hickory, elm and birch. They supplement this diet with water plants and if growing near their home, crops such as corn and peanuts.

Integrated Pest Management Strategies

1. Do nothing. Beavers are part of the natural landscape and may be valued for their dam building activity that creates wildlife habitat and stabilizes stream flow.

2. Install fences to keep beavers away from valued plants. The fence needs to be 8 to 10 inches from the plant, at least 3 feet high, made of ½-inch mesh hardware cloth or 2 by 4-inch welded wire and should completely surround the plant.

3. Install electric fencing to protect larger areas. One or two strands at a height of 4 inches are recommended.

4. Trap or shoot the beavers. In many areas, it is legal to trap or hunt nuisance beavers that are causing property damage at any time and without a permit. Check local or state regulations first. While live-trapping is an option, releasing the trapped animal is difficult and mortality of released animals is high. It may be kinder to kill the beaver humanely.

More images:

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Willow (Salix) girdled by a beaver.
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Close-up of gnawing damage from a beaver on a willow (Salix); tooth marks are visible
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Beaver damage
 
Pests and Problems

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