All About STOs

  • What is a STO?

An STO is a Brazilian Short Tail Opossum. They are a small, solitary, exotic marsupial gaining popularity as a “pocket pet”. They are from Brazil, Bolivia, Paraguay and northern Argentina. They were originally brought to the USA from Brazil in 1978 and have been bred for the pet trade since 1994.

When full grown they reach about the size of a gerbil or hamster and have a lifespan of about 4 years in captivity. They live by themselves in the wild and should be kept singly as pets.
They are known by several different names, including “Brazilian short-tailed opossum”, “South American Short Tail opossum”, “Rainforest opossum”, “Brazilian opossum” and “Laboratory opossum”. Incorrect names include “Pygmy Opossum” and “Dwarf Opossum”, and many websites incorrectly spell their name as ‘possum’, ‘opposum’ or ‘oppossum’.

  • Temperaments

Like cats and dogs, short tail opossums have very individual preferences and temperaments. Some STO enjoy attention, being petted and played with, taking treats from their owner’s hands and coming out of their cage. Some prefer sleeping in their owner’s lap, or actively climbing and investigating, and still others like staying inside their cage at all times. Some owners prefer to observe their short-tailed opossums rather than interact closely with them, and the solitary STO are perfectly happy with that.

Most pet owners keep one short tail at a time unless they are actively trying to breed. Since adults may hurt or even kill each other, even breeding pairs are housed separately before and after breeding. At one time time in the pet trade, there was an approximate 25% chance of injury or death per mating attempt.

  • Nocturnal By Nature

Short tail opossums are nocturnal; they are most active at night or in darkness, and spend much of the day sleeping. It is important for potential owners to understand this, and decide if a short tail will fit into the family routine. Try to have realistic expectations about their night schedules. Don’t expect them to be active and playful during the early afternoon, no matter how impatient you are to watch and play with your new pet. Some owners like to schedule their interaction, feeding and watching them in the evening when they are more cooperative and active.

  • Handling and Bonding

Let short-tailed opossums smell you before picking them up – they have poor eyesight and rely on their sense of smell. Some STO readily climb onto your hands, arms or clothing and can be picked up around the middle. They can also be safely picked up by grasping their tail and giving their front paws something to cling to. Many owners enjoy using a “bonding pouch” to play with their STO, wrap them in a towel in their lap, or let the STO run around with them in a closed area such as a bathroom or bathtub. Bribe liberally with treats! STO that are scared open their mouth to show 50 small teeth, however it is usually a bluff and most rarely bite, if ever.

STO can be grumpy if disturbed in their nest while sleeping. Wash your hands with mild soap before handling your STO. This is especially important after handling other pets or food, as STO may bite you accidentally if they think you smell like food. Another mildly unpleasant defensive behavior is that some STO like to go to the bathroom whenever taken out of their cage, but that can be minimized by keeping wet-wipes near the cage (and many grow out of it eventually). For more information, see the Care & Training section.
Temperature and Humidity

Short-tailed opossums are comfortable at most normal indoor home conditions. They need a temperature range between 70-85°F. The preferred humidity range is 40%-50%. More or less humidity is not usually harmful, though some STO suffer from dried and cracked ears if the humidity is too low. For more information, see the Temperature and Humidity article.
Cage Placement

Your short-tailed opossum should be placed in a warm and quiet area that is free of drafts. The cage should not receive direct sunlight or UV-light from reptile lamps because STO are susceptible to skin cancer.

In general, their cage should be kept away from other pets that may intimidate them; such as cats, dogs, large snakes and even some birds. If STO are able to smell animals they consider food (particularly rodents, even small rabbits or baby birds) they may be more likely to bite.

  • Supplies

Your short-tailed opossum needs a cage (at least 20 gallons), a nesting box, water bottle or bowl, food dish, exercise wheel (at least 8″), and climbing material or branches. They should be given soft nesting materials such as strips of paper towels, paper or cloth which they carry into their nest or burrow into for sleeping. Optionally, owners may provide a shallow dish in a corner for the STO to use as a litter box.

Many types of cages work; including tanks with a lid, wire cages with spacing of at least 1/2″ x 1/2″, reptile terrariums and the Crittertrail Three. Most owners who breed their STO use a solid tank for the mother to prevent babies from slipping through the wires.

Many owners successfully use cage beddings designed for small animals, such as CareFRESH, Cell-Sorb Plus, pine, aspen, eucalyptus, shredded paper or newspaper. Unlike rodents, STO are not destructive chewers so they can enjoy a wide range of cage types and accessories.

The need for an exercise wheel cannot be over-emphasized because it is a great source of healthy exercise and is typically the short tailed opossum’s favorite toy. Adults spend hours every night running in the wheel. They take short breaks to eat or drink, or run around their cage, and then go right back to the wheel. Since they are nomadic in the wild with large ranges, it has been speculated that the exercise wheel provides them an instinctual outlet for their energy. My short tails have been clocked at running up to 8 miles per night in their wheels!

  • Nutrition

Short-tailed opossums are omnivores that mostly eat insects, rodents and fruit in the wild. Their diet should be high in digestible protein, low in fat, with reasonable fiber and calcium. Most STO are fed soft fruits and vegetables, a high quality dry food, and supplement with live insects and/or rodents.

Most animal experts recommend dry food containing 30%+ protein, 9-13% fat with up to 5% fiber and make the dry food available all the time. Fruits and vegetables can be given fresh, frozen, pureed, or from baby food containers and are usually provided nightly then removed in the morning to prevent spoiling. Insects are typically given in small quantities of 1-5 per day, or in larger quantities once or more per week. STO are very water-dependant and need a source of water at all times.

  • Hygiene

Short-tailed opossums are generally clean and tidy animals. They groom themselves extensively, especially before and after meals. Their bodies themselves have very little odor, though males sometimes have a slight ‘musk’ smell. Another nice benefit to short-tail opossums is that they rarely (if ever) go to the bathroom in their nesting area, and many prefer to use just one area or corner of their cage for waste. Many owners can convince their STO to use a litterbox in a corner of the cage which can help make odor control easy.

If any smell from their cage is noticeable, it is usually from their waste. Because they are sub-tropical animals they tend to have moist waste, and because their diet includes meat, insects and meat-based protein there is just no getting around the fact their waste is smelly. Owners using wire cages might notice the smell more than those in tanks, but often the smell can be minimized by using an extra absorptive cage bedding, like Cell-Sorb.

One issue that is important to know is the majority of short tail opossums (even the ones that use a litterbox) also go to the bathroom while running in their exercise wheel. This can mean some very messy wheels in the morning. Usually though, owners adapt to this using different techniques. One suggestion is trying a variety of wheels until you find the best one for cleaning. (I personally use the Comfort Wheels with the mesh squares, instead of a solid wheel, because it’s easier for the waste to fall to the floor.) Some owners put a litterbox under the wheel and empty it frequently, or put clumping kitty-litter under the wheel. Owners sometimes wipe up the wheel every morning, but the need for that varies by STO so it isn’t necessary for every owner.

  • Purchasing

When looking for a short-tailed opossum to purchase, options include breeders (hobby, small-scale or large scale), retail pet stores, exotic animal shows and auctions, or exotic animal rescues and shelters. Resources can include newspaper and online classified ads, online message boards and mailing lists. Most STO are found in Texas and the Midwest. Prices for the standard gray color STO usually range $50-$100 depending on geographic availability.

Color variations of STO are sometimes also available though frequently more expensive. Some colors include gray with white feet and legs, gray with white ears, gray with white feet and white ears, rosy-reddish, golden, silver, ivory (a very light gray fur color), and a white patch on the belly.

  • Shipping

When short-tailed opossum pets cannot be found locally, many breeders will agree to ship STO during periods of warm weather via airplane for an additional $130-150. The only legal way to ship STO is via airline – it is illegal to send STO through the U.S. Mail, UPS or FedEx and attempts to do so could result in jail time and/or fines. For more information see the Shipping Laws section.

  • Legal Issues

Check with your state, county, city and municipal codes to ensure STO are legal to own in your area. Ask if you need any permits to own your STO. If you are in an apartment, check with the complex to see what pets they allow. The state agencies that usually regulate exotic pet ownership are the Fish & Game, or Department of Natural Resources.

You do not need a USDA license to own a STO.

  • Health

Their lifespan should be around 4 years in captivity. It is best to choose a healthy STO that is alert and curious with bright, clear eyes and a nose that isn’t runny. The most common health problems for STO include hair loss around the rump from a protein deficiency or cage bedding allergy (usually to pine or aspen), diarrhea from new foods, dehydration from lack of water, pneumonia from drafts or bacterial infection, or ear damage from fights, mites or low humidity. Mites are not usually a problem because their fur is so dense. Later in life, STO usually die of old age due to respiratory illness, digestive problems and tumors.

Since STO are rare, find an exotic or small pet veterinarian before a health emergency occurs. Otherwise, if your STO gets ill you may waste valuable time searching for a vet who will agree to treat your pet. Vets can be found in the phone book or referrals from other vets. Veterinarian teaching schools and local zoos may recommend good exotic vets in the area. For more information see the list of short-tailed opossum Health Concerns & Questions for more information about their common health problems and a list of vets that are willing to treat STO.

Many short-tailed opossums, particularly when young, occasionally eat their own waste products. According to several veterinarians this behavior does not indicate a health problem and it does not indicate a diet deficiency. So while gross, it’s fairly normal and the opossums usually do it less frequently as they become adults.