Solutions for Vertebrate Pests

This page provides guidance for managing vertebrate pests, including:


Bats

General Information

Bats, while extremely ecologically beneficial (they are insectivorous, important pollinators, and are a food source for large raptors), bats can become a nuisance and a human health threat when pressed out of their natural habitats and into closer contact with humans/into roosting in man-made structures. Bats hibernate during colder months and, while they often do so in caves, rock crevices and tree cavities, they will also hibernate in human-built structures, preferably those which hold to temperatures between 32-41 degrees Fahrenheit. If able, they will return to the same roosts every year.

Always work with a specialist when dealing with bats for two important reasons: 1) because of regulations: most species are protected, and 2) because of human health and safety concerns. Bats can carry and transmit disease and ectoparasites, such as rabies, histoplasmosis (spread via bat guano), and bat bugs,* which are very similar to bed bugs (*If you believe that you have “bed bugs” but have experienced recent bat activity, have an inspection to rule out bats/bat bugs. Such an inspection can save time and money by preventing recurring “bed bug” treatments when in fact the problem-causing pests are bat bugs).

Bats are most likely protected in your locality and it is probably illegal to kill bats in your area. Even the timing and process of removal is likely regulated. If bats are encountered with white nose syndrome during inspection, that should be reported to the proper authorities before removal, in case they want to retrieve specimens and/or track cases. Many species are federally and/or locally protected. Be sure to work with the appropriate wildlife or other agencies to ensure that you follow legal guidelines in dealing with vertebrate pests.

Identification

There are many bat species in North America, many of them legally protected. One of the most common varieties is the Big Brown Bat, which is found in virtually every American habitat. Big brown bats weigh between ½ and ¾ of an ounce with wingspans from 13 to 16 inches. Their fur is longish and somewhat oily and brown, while their broad snouts, short ears, and wing membranes are black.

Signs of Infestation

  • You see bat guano (bat droppings) around the home or workplace buildings 
  • You see oily streaks around certain parts of your home or buildings
  • You hear sounds in the attic
  • You see a bat in your home or inside a building
  • Your attic has a strong pungent odor (bat urine smells like ammonia)
  • You see bats flying to and from your home or structures
  • Your pet brings home a bat
  • You see stains on the ceilings
  • You see dead bats in or around the property
  • You see piles of black droppings on attic insulation

Control and Treatment

Bat removal is always a job for professional pest control operators – try to find one who specializes in bats and understands pertinent bat-related regulations. While removal can be costly, there is one fairly simple thing that you can undertake on your own: observation. If you can undertake an evening “stake out” and observe from where bats are entering/exiting a building, then alert your pest professionals to the locations of bat activity, you save having them perform this step. If you can not identify the sources of the bat activity, the pest professionals should be able to – sometimes even using camera systems to detect breaches. 

Exclusion is the main control tool used in bat management. 

The most common and straightforward way to exclude bats is using a one way device. This is usually achieved through the use of a custom fitted, semi-rigid wire mesh that allows bats to squeeze out to exit the structure, but restricts access and confuses them when they try to re-enter.  

There are specific periods during the year, generally during gestational and rearing periods, when bat exclusion is NOT permitted at all. Your removal specialist should know and abide by these legal restrictions. Rare exceptions may be made for health reasons and usually require approval from a government agency.

Remember to be on the look out for bat bugs once removal and exclusion is completed. Bat bugs can travel in search of new hosts after bats are removed.

Contracting a pest control professional to erect bat-specific artificial roosts (bat boxes) is another good option for keeping bats out of homes and buildings. Installing bat boxes near homes and buildings, in addition to providing bats with a better roosting space, encourages natural insect control and bats’ pollination activities. Make sure that they are properly installed (at the right height: 10-20 feet above ground, and in the right places: where they get approx. 7 hours/day of sunlight, etc).

Food Sources

Bats like to eat beetles, moths, mosquitoes, and more.


Birds

General Information 

Pigeons and English Sparrows (aka House Sparrows, English House Sparrows, or Moineau Domestique) are two of the more troublesome pest birds for institutions in urban environments and in small rural communities. 

These birds adapt well to man-made environments where they are able to nest and roost. Nesting materials along roof edges can clog gutters, downspouts and air intakes. Clogged gutters and downspouts can, in turn, cause moisture problems in buildings, attracting other destructive pests, like termites and silverfish. And birds’ nests alone, even those which aren’t causing blockage issues, are known to harbor many museum pests such as: psocopterans, beetles (especially Dermestidae), mites, and moths (including clothes moths). All of these pests will feed on museum specimens!

Bird fecal droppings can deface and damage buildings and statues, and the fecal droppings of particular species may carry diseases such as histoplasmosis, encephalitis, pigeon ornithosis, Newcastle disease, crytococosis, toxoplasmosis, pseudo-tuberculosis, pigeon coccidiosis, and salmonella food poisoning. Further, some of the ectoparasites of pigeons, such as chewing lice, fleas, ticks and mites, can transfer to people. While a live bird’s presence and activities pose immediate threats to collections and building interiors/exteriors, bird carcasses are also highly problematic, as they can trigger still more pest infestation (by, for example, webbing clothes moths or dermestids, like carpet beetles). This Case Study shared by Christina Cain from the Denver Museum of Art illustrates what can happen when an infestation derived from a bird carcass strikes.

Identification

Visit Cornell’s All About Birds online bird guide for more information on specific bird species, their habitats, behaviors, and identification tips.

Many species of birds are federally and/or locally protected. Be sure to work with the appropriate wildlife or other agencies to ensure that you follow legal guidelines in dealing with avian pests.

Signs of Infestation

Often the first signs of infestation are the birds themselves. Many species (and often the nestlings  especially) are very vocal throughout the day and are conspicuous in their habits. Noisy nesting birds may even be heard through interior walls. 

Signs that birds may be nesting in the nooks and crannies of building may include:

  • Nesting materials (for example, feathers, twigs, grasses, scraps of paper, mud, etc.) tucked around discrete spots on the exterior of the building, for example: along ledges, roof edges, or soffits
  • Concentrated areas of fecal material on the ground around or on the sides of buildings
  • Entrance holes where birds can be seen entering and exiting cavities
  • Birds seen transporting nesting materials to and fro 

Control and Treatment

The most effective control and treatments rely upon exclusion techniques – especially for deterring nesting birds. As part of any exclusion plan, existing nests should be removed and any holes or crevices in external building structures should be filled or closed off. Control is most effective when preventing birds’ access to safe/easy nesting spots in and on buildings.

Various bird deterrents are commercially available. These deterrents operate in several different ways, and researching which methods work best for which type of birds, or birds of your area may prove prudent.

  • Chimney caps, dampers, and mesh gutter covers discourage nesting and bird activity.
  • Bird spikes can help as a landing/nesting deterrent, but they require maintenance (such as removing nesting material that may be deposited on top of the spikes). Spikes may not entirely eliminate bird dropping issues. Most pest companies will not install spikes without a maintenance contract attached to the installation of these spikes. Potential locations for spike installation may include parapet walls, roof lines, ledges, sills, eaves, etc. 
  • Bird deterrent wires are a sleek almost invisible way to prevent birds from perching/nesting. These cost more upfront, but are more effective than spikes and present a much cleaner/more minimal aesthetic. These should not require a service maintenance contract.   
  • Sound, air, or water delivery devices are available. These are, however, rarely used near museum settings, and certain birds can become inured to these methods of deterrence.
  • Ultrasonic bird control devices properly mounted can be useful in loading dock situations to run birds out of large spaces.  

Food Sources

While many birds eat seeds, berries, and insects, others like the House Sparrow and Pigeon have adapted to eat almost any grain product and will thrive on handouts of bread, crackers, and snack foods. Posting signs for patrons to NOT feed birds is another possible control technique.



Mice and Rats

Mouse on museum stagecoach (C. Sullivan, NPS)

General Information

Although there are other types of rodents that can wreak havoc on buildings and grounds, mice and rats are the primary rodents that consistently seek harborage inside buildings and storage spaces.

Where can I find general guidance on IPM for rodent control? 

What do I need to know to protect my health and safety when handling mouse- or rat-infested materials?

Identification

The three most common species of pest rodents are the Norway rat (Rattus norvegicus), the roof rat (Rattus rattus), and the house mouse (Mus musculus), all of which were introduced to North America. There are also native rodent species, though they are less often associated with damage and typically avoid humans. Deer mice and white-footed mice (Peromyscus sp.), as well as meadow mice (Microtus sp.) are exceptions, and may live around or in buildings. Visit the NPS manual on Commensal Rodents for more details.

  • Norway rats are also known as wharf rats, sewer rats, or brown rats. Adults range in size from 12-18 inches (30-46 cm) from nose to tip of tail, and weigh 12-16 ounces (200-500 grams). It has a blunt nose, small hairy ears, and its body is longer than its tail. They are found throughout the United States.
  • Roof rats are also called black rats or ship rats. They are not as stocky as Norway rats, weighing 5-9 ounces (150-250 grams), and measuring 13-18 inches (33-46 cm) from nose to tip of tail. It has a pointed nose, larger hairless ears, and its tail is longer than its body. They are found mostly in coastal areas.
  • House mice weigh from ½ to 1 ounce, and vary in color from light brown to dark gray. They have moderately large ears and nearly hairless tails that are roughly the same length as their body. They are found nearly everywhere that there are humans.
  • Deer mice and white footed mice sometimes become pests when they enter buildings adjacent to woodland or fields. They are similar in size to house mice, with white feet and undersides, and brownish upper surfaces.
  • Meadow mice or voles (Microtus sp.) sometimes become a pest in structures. Unlike house mice, they are less agile, with larger, bulky bodies, shorter tails and small ears and eyes.

Signs of Infestation

How do I know if I have a mouse or rat infestation?

Control and Treatment

How do I pest-proof my facility to prevent a mouse or rat infestation?

Where can I find guidance about rodent exclusion for new construction?

How do I set up a trapping program to monitor for mice and rats? 

Food Sources

Mice and rats feed on a wide variety of foods.

  • Norway rats prefer protein-based foods such as meat, fish, insects, pet food, nuts, and grain. They will readily feed on human garbage.
  • Roof rats prefer plant foods such as fruits, nuts, seeds, berries, vegetables, and tree bark. They will occasionally feed on human garbage.
  • Mice feed on cereals, as well as foods high in fat and protein (butter, nuts, meats, etc.), as well as sweets, including chocolate.


Opossums

General Information

Opossums are nocturnal marsupials with a variety of species globally. Omnivorous, they are excellent at insect and rodent pest control, but will also readily scavenge for food in trash cans and dumpsters. They are skilled climbers and easily gain access to rooftops/attics via tree branches and power lines. Alternatively, they may burrow under sheds or decks to take shelter and protect their young, as they prefer nesting in enclosed spaces, safe from the elements and predators.

Opossums rarely carry rabies due to their low body temperatures and high immunity, but they can host parasites like fleas, ticks, mites, and lice. Flea infestation can lead to the transmission of flea-borne typhus. Opossums have also been known to carry tuberculosis, leptospirosis, tularemia, spotted fever, trichomoniasis, chagas disease, coccidiosis, and more. 

If they become a nuisance and removal is necessary, contracting a trained pest professional is essential.

Some species may be federally and/or locally protected. Be sure to work with the appropriate wildlife or other agencies to ensure that you follow legal guidelines in dealing with vertebrate pests.

Identification

There is one native species of opossum in North America, the Virginia opossum (Didelphis virginiana), commonly known as the North American opossum. They are roughly the size of a house cat, ranging between 24 and 40 inches long, including a 10-12 inch tail length, and 50 teeth. They have long, coarse light to dark gray fur with black or dark brown under fur and a white face. They also have long, pointed snouts with a distinctive pink nose, a scaly, nearly hairless, prehensile tail, and rounded hairless ears. “Playing possum” is another characteristic feature – they will essentially appear to be dead as a nervous shock reaction. They will slow the heartbeat, roll onto their side, go limp, shut their eyes, and let their tongue hang out. 

Signs of Infestation

A visual sighting of an opossum is the best method of identifying an opossum pest concern, although they are only active at night and low-light hours. They are messy eaters, so you may find remnants of the previous night’s feeding. Opossum tracks are also distinctive, as they have five finger-like toes on both fore and hind prints and an opposable thumb on each hind foot, which generally will print at an angle of 90 degrees or greater to the other four toes.

Control and Treatment

Opossums are generally beneficial to the ecosystem, but if they become a nuisance, trapping is the best method of removal. It is necessary to consult a pest professional for trapping.

  • Trap size 30”x11”x12”
  • Baits: Apples, oatmeal cookies, and peanut butter are effective baits 
  • Dog or cat food, meat, or meat-by products should not be used because domestic cats are highly likely to be caught
  • Please check locality for any trapping laws

Other methods to discourage opossums from establishing nests include:

  • Remove food sources (secure dumpsters/garbage/composts at night and remove fallen fruit from trees)
  • Trim tree limbs to prevent easy access to roofs/attics
  • Block access points into basements, attics, etc. and fence-in bottoms of porches/decks

Food Sources

Opossums are omnivorous and will eat a variety of foods including carrion, eggs, ticks/insects, small mammals, fruits, nuts, seeds, birds, frogs, worms, and garbage. Aggressive scavengers, they are attracted to unprotected garbage cans and dumpsters that are left open.


Raccoons

General Information

While raccoons prefer living in wooded areas with access to trees and water; building dens in hollow trees or abandoned burrows, they are also extremely adaptable and can make homes in attics, sewers, barns and sheds. Raccoons often enter attics and chimneys in the spring, right around their breeding season (February to March). They are omnivorous, dexterous, and nocturnal, having been known to roll up freshly laid sod in search of grubs and releasing locks on trash cans and dumpsters in search of food late at night. They can be structurally destructive when trying to gain access to buildings. Further, racoons can carry dangerous diseases, such as rabies, canine distemper, parvoviruses, leptospirosis, salmonella, and roundworms. They can also be infested with ticks, lice and fleas. 

Some species may be federally and/or locally protected. Be sure to work with the appropriate wildlife or other agencies to ensure that you follow legal guidelines in dealing with vertebrate pests.

Identification

There is one species of raccoon found in North America, the common raccoon (Procyon lotor). They have bushy, oily gray fur with a black mask around the eyes, 4-7 black rings around the tail, a pointy snout with a black nose and black front paws. Racoons can be 16 to 30 inches in length, and weigh 10 to 30 lbs.

Signs of Infestation

  • Strong smell of feces and/or urine
  • Outside damage to your roof/soffits/eaves
  • Oily, dark stains around holes in walls or fascia where raccoons enter/exit frequently
  • Scratching, scurrying, chattering noises at night in ceilings and walls
  • Household pets acting oddly
  • Tipped garbage cans/strewn garbage
  • Tracks in soft soil/mud in flower beds and gardens

Control and Treatment

  • Chimney caps
  • Closing/securing openings for exclusion
  • Securing trash bins and dumpsters
  • Removing/securing food sources

Trapping

  • Live trap size: 30”x11”x12”
  • Bait: marshmallows, fish-based cat food*, or  fried chicken* (*Use a few drops of anise oil with these baits to avoid attracting domestic cats – or just use marshmallows.)
  • Please check locality for trapping/releasing laws

Food Sources

Racoons are opportunistic omnivores and will eat human garbage, insects, fruits, nuts and seeds, and smaller animals like frogs and snakes.


Skunks

General Information

Skunks have very conspicuous black and white coloration and a strong-smelling musk they spray when threatened. They are, unfortunately, easily startled, as they have poor eyesight and mostly hunt by smell and hearing, but they will sometimes give a warning before spraying: stomping their feet and arching their back. Striped skunks have the largest range of the five skunk species in the U.S.  and exist in every state except Alaska and Hawaii. Nocturnal omnivore/insectivores, skunks may dig up lawns in search of grubs and can disturb unprotected trash in pursuit of food. Skunks may dig their own dens for their families or enlarge an existing den, such as a groundhog burrow. They are also known to burrow under porches and crawl spaces, and young skunks can sometimes get stuck in window wells. Skunks can carry dangerous diseases, such as rabies, leptospirosis,distemper, zoonoses, canine hepatitis, and intestinal roundworms. They can also be infested with ticks, lice and fleas, which can transmit Lyme disease, anaplasmosis, and ehrlichiosis to humans.

Some species may be federally and/or locally protected. Be sure to work with the appropriate wildlife or other agencies to ensure that you follow legal guidelines in dealing with vertebrate pests.

Identification

Skunks are stout, small, fluffy animals with stumpy legs. They have small heads, short, pointed snouts, and small black eyes and strong claws for digging. Their most distinctive feature is the white stripes that run along their backs and extend to the tips of their long, fluffy tails.

Signs of Infestation

  • 3”- 4” Holes in your turf
  • Visible burrow especially under porches
  • Telltale odoriferous scent

Control and Treatment

Be sure to work with a pest control professional for removal. Ensure they use COVERED live traps, roughly size 24”x 7”x 8” in size. Make sure that the cover is installed at the time or trap installation as the cover protects and shields from spray.

Bait: Canned fish (sardines), crisp bacon, bananas, or bread coated with peanut butter. Bananas or crisp bacon work best. If sardines are used, place a few drops of oil of anise around the trap so as not to capture domesticated cats.

For skunks trapped in window wells, place a piece of lumber (2” x 4”) in the window well angled up and they will crawl out on their own if you leave them alone. If they do not move on, then see trapping above.

Other methods to discourage opossums from establishing nests include:

  • Remove food sources (secure dumpsters/garbage/composts at night and remove fallen fruit from trees)
  • Block access points into basements, attics, etc. and fence-in bottoms of porches/decks 
  • Block abandoned groundhog holes 

Remember a skunk’s defense mechanism is caustic odiferous spray!!!

Food Sources

Skunks are omnivorous, eating insects, larvae, vegetables, fruits, grains and garbage.


Squirrels

General Information

There are several squirrel species which can cause damage to historic structures (to, for example, exterior wooden architectural details and electrical wiring) and soft metal structures, such as lead garden statuary. Damage caused by squirrels is largely related to their energetic chewing, but can also result from nesting activities, which may attract chewing lice, fleas, ticks and mites which can transfer to people. Some species are federally and/or locally protected. Be sure to work with the appropriate wildlife or other agencies to ensure that you follow legal guidelines in dealing with vertebrate pests.

Identification

  • Eastern Grey Squirrel
    The Eastern Grey Squirrel may be grey, reddish-grey, or black in color. It is diurnal (active during the day). They measure 16-20 inches long and 1.25 to 1.75 pounds. The Eastern Grey Squirrel occupies a range of 2 to 7 acres. Eastern Grey Squirrels are known to do damage to electrical wiring, fascia and soffits, and to leave greasy rub marks along frequently traveled routes.
  • Red Squirrel
    Red squirrels are smaller than grey squirrels, and diurnal (active during the day). They have a red coat and prefer pine forests.
  • Southern Flying Squirrel
    Southern Flying Squirrels are 8 to 10 inches long with a membrane of skin stretched between front and rear legs, a line of demarcation between upper and lower coat, and a flattened tail. They are nocturnal. In some areas flying squirrels are protected, so it is important to verify species and check local laws pertaining to what actions are legal.
  • Delmarva Fox Squirrel
    At 18 to 27 inches and 1.75 to 2.25 pounds, the silver grey Delmarva Fox Squirrel is larger and more terrestrial than the Eastern Grey Squirrel. It was delisted from the Endangered Species list in 2015, so check local laws to determine whether it is still protected in your area. 

Signs of Infestation

The first signs of a squirrel infestation are usually the squirrels themselves. There may be increased activity around the property, increased population numbers, chewed or damaged entry points (teeth marks), noise, droppings, and damage to insulation, electrical wiring, fascia, soffits, roofs, etc. Squirrels often also leave greasy, dark, rub marks on entry points.

Control and Treatment

Exclusion:

  • Exclude at entrances/exits.
  • Consider removing bird feeders or using feeders that have squirrel deterrents.
  • Post “Do Not Feed the Squirrels” signage.
  • Pick up fruit/seeds/acorns from and/or around trees.
  • Cut/prune tree limbs away from structures to discourage easy access to rooftops and attics.

Trapping:

  • Trap size: 18”x5”x5”  
  • Baits: Cereal, grains, nuts (peanuts), sunflower seeds, shelled corn, mixed peanut butter and oatmeal, or mixed peanut butter and molasses
  • Traps must be checked daily.
  • Please check locality for any trapping laws.

Food Sources 

Squirrels eat grains, nuts, seeds, berries and fruits, and more, but they have also adapted to living near humans and will happily eat human-food cast-offs, such as old sandwiches and sweet snack foods. Posting signs for patrons to NOT feed squirrels is another possible control technique.


Woodchucks

General Information

Woodchucks, a.k.a. groundhogs, whistle pigs, marmots, are closely related to squirrels. Their chambers can be up to 50 feet long and usually consist of a main entrance, plunge hole, nest chamber, and restrooms. Below are helpful suggestions to make sure your pest control professional is successful. Woodchucks (a.k.a. groundhogs, whistle pigs, marmots), while closely related to squirrels, display very different behaviors and pose very different threats. Woodchucks live in underground burrows which can be up to 50 feet long and consist of several chambers: a main entrance, a plunge hole, a nest chamber, and restrooms. The main problem posed by woodchucks is damage to the landscape, rather than damage to historic structures or collections spaces. Woodchucks, through their burrowing, create hard-to-see holes and pits (up to one foot in diameter) in lawns/grounds which pose tripping hazards for visitors and staff. It is essential to work with a pest control professional to remove woodchucks from a premises. Below are helpful suggestions to make sure your pest control professional is successful.  Many species are federally and/or locally protected. Be sure to work with the appropriate wildlife or other agencies to ensure that you follow legal guidelines in dealing with vertebrate pests.Woodchucks, a.k.a. groundhogs, whistle pigs, marmots, are closely related to squirrels. Their chambers can be up to 50 feet long and usually consist of a main entrance, plunge hole, nest chamber, and restrooms. Below are helpful suggestions to make sure your pest control professional is successful. 

Identification

Woodchucks have brown and grey fur, small ears, long incisor teeth, and short, strong legs and clawed paws for digging. They often grow up to 20 inches in length, with a flat tail that measures roughly six inches long, and they weigh between six and 12 pounds. They are diurnal (active during the daytime) and herbivorous. Their breeding season is March to April, and hibernation is from November to March. They do not tend to travel far from their dens and are often found near to gardens.

Signs of Infestation

The most common signs of a woodchuck are large holes or pits in the ground which can be 10 to 12 inches in diameter and are usually found close to a tree or the foundation of a building. There are often mounds of dirt surrounding the main entrance hole, although secondary exit holes may not have dirt mounds.

Control and Treatment

Exclusion is not usually a viable solution to woodchuck issues, so trapping is the most effective approach. It is essential to work with a pest control professional to remove woodchucks.

  • Recommended live trap size: 36”x11”x12”
  • Recommended baits: peaches, apples, strawberries
  • Check your locality for any trapping/releasing regulations

Food Sources

Woodchucks are herbivores and like garden veggies (lettuce, carrots, fruits, etc.), tree bark and twigs, ground cover crops and weeds like alfalfa, clover, and dandelions, and insects.


Created 2017, Updated 2022

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