Animal Library: Mouse Opossums

Please enjoy this information based on our experience, but we no longer breed the animals below, or have any contacts for them.

Mouse Opossum

Southern Mouse Opossums (Fat Tailed Opossums) DIDELPHIMORPHIA; MARMOSIDAE Genus THYLAMYS

History of Mouse Opossums at Millermeade Farms

Our original, unrelated breeding trio was the first generation from imported animals. 
Our first trio bred successfully four times but we were not able to produce any babies from the second generation. 
In order to introduce new bloodlines to our animals we purchased some older, imported animals but we did not have any breeding success with the new animals.
In hopes that a change of environment would spark some reproduction we shipped our mouse opossum colony to an opossum enthusiast in Colorado. 
Unfortunately the opossums were left on the airport tarmac in Atlanta during flight transfer and half died due to over heating. 
To our knowledge, there is no one currently breeding mouse opossums in the U.S. or Canada.

Habitat and Origin

  • There are several genera that are often collectively referred to as mouse opossums.
  • When our species of mouse opossums were first introduced to the pet market they were often mistakenly classified as Thylamys elegans, Marmosa elegans, or Marmosa murina.
  • With the help of Ms. Molly Joy Kalafut and Dr. Alfred Gardner they have been more accurately identified as Thylamys pusilla (also known as Thylamys pusillus).
  • The genus Thylamys has five species including T. elegans, T. macrura, T. pallidior, T. pusillus, and T. velutinus (Nowak).
  • Most mouse opossums live in Central and South American tropical rain forests, especially along the Amazon Orinoco River basins and adjacent lower parts of the Andes Mountains (American Zoo). Some species can be found in the Argentine grasslands and as far north as Mexico (Nowak).
  • T. pusillus is a found in Argentina, Bolivia, Brazil, and Paraguay (Nowak).
  • Mouse opossums typically live in trees but they will take advantage of other small nests and burrows made by other animals or in other naturally occurring hiding places such as hollow logs or under rocks.
  • Like most opossums, murine opossums are nocturnal and have minimal daylight activity.

Physical Characteristics

  • Mouse opossums vary in size and in coloration but all have facial markings around the eyes.
  • Our mouse opossums had approximately a four-inch (10 cm) body and 3 3/4 inch (9 cm) tail. Our first male mouse opossum was of an average size for T. pusillus and weighed 38 grams (approximately 1 1/3 oz) and our females were slightly smaller.
  • All mouse opossums have a prehensile tail that is used to carry various bedding materials and as a climbing tool. Some mouse opossums have been observed hanging upside down by their tail while eating.
  • The Thylamys genus is unique in that it can store fat in its tail. The tail will look very plump or swollen, which is often termed incrassate (Nowak). The fat deposits help them survive the cold and arid areas where food is difficult to come by (Kalafut).
  • Mouse Opossums are a true marsupial but they do not have a pouch like many other opossum species. When the babies are born, they attach directly to the mammary nipple on the female’s abdomen.

Habits and Personality

  • Our mouse opossums had a personality similar to a mouse but a little more timid. If handled frequently they seemed to be easily tamed and will very easily bond.
  • When mouse opossum are startled they will often freeze in place or they might run and look for a place to hide. They will also crinkle their ears and lower them to their body like a sail when they are scared.
  • Mouse opossums may exhibit a defensive, opened mouth hiss when you reach in their nest to pick them up until they learn to trust you. This bluff is common in other types of opossums as well. The hiss lets you know that they are scared but they will typically try to escape rather than bite. They usually will only bite if they fell threatened. Any animal with teeth can bite so even though they are little they should be treated with respect.
  • It is never a good idea to startle a sleeping animal or grab or chase an animal since these actions make the animal feel threatened and they will act accordingly.
  • Mouse opossums enjoy hiding places and will typically spend their sleeping hours in seclusion.
  • Mouse opossums are solitary animals in the wild so we housed our mouse opossums individually. We have witnessed mouse opossum aggression towards siblings by the age of 16 weeks.
  • We believe they make excellent pets since they have little odor, are fun to watch, and have charming personalities. We have had many excellent reports from our mouse opossum customers and they have been very happy with their new pets.

Cage and Equipment Requirements

  • All pets enjoy plenty of room to run, play, and explore. Mouse opossums are fairly small so a 15-gallon aquarium provides plenty of room for hiding places and jungle gym type structures.
  • Tall, vertical cages, rather than long, horizontal cages, are ideal for providing room for branches and other climbing structures.
  • A tight fitting lid is necessary since mouse opossums are good jumpers and climbers.
  • We do not recommend any type of wire caging. These little guys are amazingly flexible and great escape artists.
  • Mouse opossums tend to use the bathroom in various areas of their cage and on accessories. Accessories should be easy to clean or disposable.
  • Habitrails or other plastic tubes and tunnels systems may be used inside their primary enclosure but not as their main cage unless there are no wire bars as part of the cage.
  • A mini or mouse size rodent safe wheel with a solid floor is a good addition to a mouse opossum cage.
  • Mouse opossums do not chew plastic like small rodents so plastic accessories are ideal because they can be easily cleaned.
  • We have found that our mouse opossums enjoy multiple hiding boxes. They do not sleep in the same spot all the time. Other accessories may include clay flowerpots, toilet paper tubes, and objects to hide under.
  • We put bedding material in their nests but the mouse opossums do not seem to make nests on their own as most small rodents are known to do.
  • Pine, aspen shavings or other wood products are the most commonly used beddings for other small mammals but we do NOT recommend using it for mouse opossums. It is reported that some mouse opossums are allergic to certain types of wood products. Never use cedar shavings because the oils and dust from cedar can be harmful to small mammals.
  • I personally prefer the soft fluffy paper type bedding or a product called Cell-Sorb since it doubles as excellent nesting material.
  • Many mouse opossums love to tunnel and burrow so several inches of bedding in their cages is a good idea. 

Food, Water, and Temperature Requirements

  • Mouse opossums as a group are generally considered omnivorous, but Ian Hume reports in his book Marsupial Nutrition that they probably include more animal than plant material in their diets.
  • We have tried many different dry foods including: Happy Glider Sugar Glider Food (Pet Pro Products), Spike’s Delite Premium Hedgehog Food (Pet Pro Products), Special Kitty Cat Food (Wal-mart), Mazuri Insectivore Diet, Chicken Soup for the Cat Lover’s Soul Lite (Diamond), and Insectivore-fare (Reliable Protein Products). We provided a lot of variety in the dry portion of their food since not a lot is known about their diet in captivity.
  • Pet Pro Products has a variety pack of sugar glider foods that has apple, peanut, chicken, and cherry flavor. One of the flavors can be substituted for Spike’s Delite Hedgehog food. By using the variety pack you can provide a variety in the dry foods without having to purchase very large quantities of dry food at one time.
  • Our mouse opossums ate less than a teaspoon of dry food every day.
  • We believe insects should also be included in the mouse opossum’s diet. We raise our own mealworms so we use mealworms as our main supplemental insect but they do enjoy crickets too. Mealworms have a high fat content and should be fed in moderation. Mouse opossums might also enjoy cooked eggs and boiled chicken.
  • We also provided diced fresh fruit and/or blended fruit (baby food) to our mouse opossums every day. Good fresh fruits to try are: apples, pears, peaches, bananas and mangos. Favorite baby food flavors are: apple, banana, banana yogurt, peach, pear, and prune.
  • Mouse opossums need to be kept out of drafts and at a reasonably warm room temperature. A comfortable temperature is 70F to 80F. We have noticed that our mouse opossums were less active and their body temperature decreased at cooler temperatures.

Reproduction & Health

  • Our first female was put into breeding 3/11/04 and was taken out of breeding on 3/25/04 and her litter was born on 4/7/04.
  • Our second female was put into breeding 3/31 and was taken out of breeding 4/15/04 and her litter of was born on 4/19/04.
  • Based on our success and research we are estimate the gestation time is approximately 14 days.
  • Some species of mouse opossums will breed all year round and others are seasonal breeders. Our mouse opossums have bred all year round but they were difficult to breed.
  • A typical litter size is said to be 7-9 in the wild and we have found this to be true in captivity.
  • The only curious health situation we have observed in our mouse opossums was a swelling in their tail. The swelling is caused by fat storage and a moderately plump tail is considered normal. A thin, mouse-like tail is typical for young animals or animals in poor health.
  • A tail that is fat to the point that it doesn’t bend very well is probably not comfortable for the animal or good for the overall health. Decreasing the fat content of their food should help this problem.
  • Mouse opossums have not been kept in captivity long enough to determine their maximum life span. Some of our imported mouse opossums have been in captivity for 2 ½ years and are still active and healthy. Our original trio is not quite two years old. If we are lucky mouse opossums will live 3-4 years.


American Zoo -- Retreived July, 2004
Gardner, Alfred L. Smithsonian. Wild Research Division. Email Correspondence 2004.
Hume, Ian D. Marsupial Nutrition
Iwokrama International Centre for Rain Forest Conservation and Development -- Retrieved July, 2004
Kalafut, Molly Joy. Email Correspondence 2004.
Nowak, R.N. (1991).Walker’s Mammals of the World (5th ed.). Baltimore and London: The Johns Hopkins University Press.

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