Mammals 105 Chapter 2
The Rodents - Rats, Muskrats and Nutria
Unlike the cute Chipmunk, the other rodents that are found around bodies of water aren’t nearly attractive enough to escape more radical deterrent measures, and the damage they can cause can be ample reason to go “postal”. We don’t need to go into how destructive rats can be when they burrow into the rocks and make nests out of geotextile and liner. The techniques that deter the larger rodents works for the smaller as well, so let’s just talk about the big guys. I was introduced to the Big Rats some years ago, when we were called in to investigate the fast-disappearing waters of a 50’ wide pond near a wetland on the North Shore of Long Island. The level of the 5’ deep pond had dropped in the strangest manner, 6-8 inches at a time, staying stable for a week or so before dropping another 6-8”. Over the course of a month or two, the pond had only 2’ of water left, and the pond owner was frantic. The mystery was solved when we finally found the first of a series of holes between the large Moss Rocks that lines the inside of the pond.
By National Park Service [Public domain], via Wikimedia Commons
Our culprits were a family of Muskrats, the only members of the single species Ondatra, native to North America but now distributed world-wide due to some very poor choices by “fur farmers” over the last century or two. The mystery of the “punctuated leakage” was explained by their charming habit of digging the entrances to their burrows just below water level. The water level would drop below the burrow, the muskrats would start to feel uncomfortable and dig a new burrow, and the water level would drop again. We had to hire the services of a local trapper to capture the pesky varmints before we completely rebuilt the pond, this time with a layer of galvanized chain link fencing underneath geotextile over the new liner.
The same brilliant “fur ranchers” introduced an even more damaging rodent pest to the States, first to California in 1899, then into fur farms in the South. Since they escaped from farms in Louisiana during an unexpected hurricane in the 1940s, Nutria, or Coypu, have become a major pest across the continent and the world. The most destructive rodent, economically speaking, next to the Rat, Nutria consume 25% of their body weight every day, eating only the base of plants such as water lilies and cattails, leaving all the stems and leaves to die uneaten. Nutria have been so devastating to wetlands that bounties have been set on their heads – no, their tails – worth $5 each in Louisiana, for example.
So, you think you may have a Giant Water Rat in your backyard. You’ll want to know how to tell the difference between them, and how to keep them at bay. The good news is the species are easily told apart by their tails. Nutria, like true Rats, have round, hairless scaled tails, along with giant orange teeth. You’ll be able to tell them from Rats by their size – Nutria over 20 pounds are not uncommon! Muskrats have a hairless tail too, but it’s flattened vertically to aid in swimming, unique among mammals, and they only get to about 4 pounds. Of course, if you find an enormous rat-like creature with a huge tail that’s flattened horizontally, you’re looking at a Beaver, the largest North American rodent.
Regardless of the species, there’s only one way to defeat them, the same way that Chipmunks are discouraged from chewing through liners, just on the inside of the liner rather than the outside. To completely eliminate the potential for aquatic rodent damage, cover the liner with geotextile, then place a layer of galvanized wire hardware cloth or chain link fencing over the geotextile. As with the small mesh hardware cloth that thwarts Chipmunks, be careful not to leave a lot of sharp points that might puncture the liner. Cover the mesh with another layer of underlayment before installing stone. It’s certainly not the easiest preventative measure, but the only one that will work against these very destructive rodents.
Poison is never a safe option! Too many other visitors to your pond will relish the opportunity to eat these tasty varmints, dead or alive, spreading the poison into the food chain, potentially into your home via an unwary dog or cat. Trapping them is a much safer option.
Unlike the cute Chipmunk, the other rodents that are found around bodies of water aren’t nearly attractive enough to escape more radical deterrent measures, and the damage they can cause can be ample reason to go “postal”. We don’t need to go into how destructive rats can be when they burrow into the rocks and make nests out of geotextile and liner. The techniques that deter the larger rodents works for the smaller as well, so let’s just talk about the big guys. I was introduced to the Big Rats some years ago, when we were called in to investigate the fast-disappearing waters of a 50’ wide pond near a wetland on the North Shore of Long Island. The level of the 5’ deep pond had dropped in the strangest manner, 6-8 inches at a time, staying stable for a week or so before dropping another 6-8”. Over the course of a month or two, the pond had only 2’ of water left, and the pond owner was frantic. The mystery was solved when we finally found the first of a series of holes between the large Moss Rocks that lines the inside of the pond.
By National Park Service [Public domain], via Wikimedia Commons
Our culprits were a family of Muskrats, the only members of the single species Ondatra, native to North America but now distributed world-wide due to some very poor choices by “fur farmers” over the last century or two. The mystery of the “punctuated leakage” was explained by their charming habit of digging the entrances to their burrows just below water level. The water level would drop below the burrow, the muskrats would start to feel uncomfortable and dig a new burrow, and the water level would drop again. We had to hire the services of a local trapper to capture the pesky varmints before we completely rebuilt the pond, this time with a layer of galvanized chain link fencing underneath geotextile over the new liner.
The same brilliant “fur ranchers” introduced an even more damaging rodent pest to the States, first to California in 1899, then into fur farms in the South. Since they escaped from farms in Louisiana during an unexpected hurricane in the 1940s, Nutria, or Coypu, have become a major pest across the continent and the world. The most destructive rodent, economically speaking, next to the Rat, Nutria consume 25% of their body weight every day, eating only the base of plants such as water lilies and cattails, leaving all the stems and leaves to die uneaten. Nutria have been so devastating to wetlands that bounties have been set on their heads – no, their tails – worth $5 each in Louisiana, for example.
So, you think you may have a Giant Water Rat in your backyard. You’ll want to know how to tell the difference between them, and how to keep them at bay. The good news is the species are easily told apart by their tails. Nutria, like true Rats, have round, hairless scaled tails, along with giant orange teeth. You’ll be able to tell them from Rats by their size – Nutria over 20 pounds are not uncommon! Muskrats have a hairless tail too, but it’s flattened vertically to aid in swimming, unique among mammals, and they only get to about 4 pounds. Of course, if you find an enormous rat-like creature with a huge tail that’s flattened horizontally, you’re looking at a Beaver, the largest North American rodent.
Regardless of the species, there’s only one way to defeat them, the same way that Chipmunks are discouraged from chewing through liners, just on the inside of the liner rather than the outside. To completely eliminate the potential for aquatic rodent damage, cover the liner with geotextile, then place a layer of galvanized wire hardware cloth or chain link fencing over the geotextile. As with the small mesh hardware cloth that thwarts Chipmunks, be careful not to leave a lot of sharp points that might puncture the liner. Cover the mesh with another layer of underlayment before installing stone. It’s certainly not the easiest preventative measure, but the only one that will work against these very destructive rodents.
Poison is never a safe option! Too many other visitors to your pond will relish the opportunity to eat these tasty varmints, dead or alive, spreading the poison into the food chain, potentially into your home via an unwary dog or cat. Trapping them is a much safer option.
