Make your own free website on

Exotic Pet Info

All About STO's

Shelter Directory
All Creatures Care
My Pictures
Pet Pictures Sent in
Sugar Gliders
Fennec Foxes
Flying Squirrels
Prairie Dogs
Big Cats

About Short-Tailed Opossums

Known as short-tailed opossums (STO for short). The Latin name is Monodelphis domestica. Some people call them Brazilian opossums, short tail possums, short tailed possums and even pygmy possums (though they aren't technically pygmies!).
These are some of the characteristics that make them so interesting:
 Prehensile tail
 Opposable toes on their back feet
 "Pouchless" marsupial - the young gestate while attached on the outside to the mother
They stay very small - full grown weight is 4-6 ounces. Their lifespan is about 6-8 years.
They can be very sweet, snuggly pets who enjoy climbing and exploring, as well as cuddling in your hands or lap to sleep.
Short-Tailed Opossum Mailing List / Yahoo Group

Click to subscribe to short-tailed-opossum
Join this way for email and web access (includes access to photos, files, polls, links and calendar)
Subscribe to short-tailed-opossum 
Powered by 

Join this way for ONLY mailing list email (no access to photos, polls, links or database entries)
View The Short-Tailed Opossum Group - Viewable message archives, even if yyou don't join!
STO Group FAQ - Covers introduction and administrative topics - how to join, unsubscribe, etc.
STO Group Rules and Guidelines - Please review when joining.
This list is for anyone interested in short tailed opossums...information about them as pets, housing, food, toys, breeding, where to buy.
You may want to join this list if you:
Want to know if a STO is the right pet for you and your family
 Want to buy a STO and are looking for a breeder
 Are a breeder looking to sell STO's
 Have a STO and want to learn or share information about them
 Used to have a STO and want to share your experiences
This group has a searchable archive of messages, lists of website references to learn more about STOs, a place to share pictures, and fun polls to participate in. You can search and read the archives to see if others have already discussed topics you're interested in.

STO Meetup

find out more at
Short-Tailed Opossums As Pets
This is an in-depth look at STOs as pets. It is a compilation of my experiences and observations, and what I’ve heard from other STO owners, websites and books. It’s kind of long, but I hope it is useful and informative!
About Short-Tailed Opossums (STO)
The short-tailed opossum is called by a variety of names, including:
 Monodelphis domestica
 Short tailed opossum
 Short tail possum
 Gray short tailed opossum
 Brazilian short tailed opossum
 Possibly Catita or Katicha in their native Brazil
They are a pouchless marsupial. Their young attach to the mother’s nipples in an embryonic stage and are visible while they develop. This makes them a popular laboratory animal for research, because it is easier to study how they develop. They have 50 teeth (can be scary looking, but they aren’t usually inclined to bite). Females have 13 nipples.
They are one of over a dozen opossums native to South and Central America. They are primarily found in Brazil, Bolivia and Paraguay. In their native environment they are semi-arboreal and enjoy climbing – right now mine is climbing all over my lap and arms while I type! In the wild they are nomadic, and eat insects and small rodents, even snakes and spiders. Nine STO were brought to the United States for the National Zoo in the 1980’s, and are slowly becoming a more popular small exotic house pet. In the wild, STO have territories of up to 5 miles per opossum and are very solitary. Do NOT house more than one STO together, otherwise you will probably end up with dead or very injured pets! STO are frequently hostile even during breeding and may injure a mate.
Personality Characteristics
All STO are very cute, unusual and entertaining to watch. They are adept at climbing and exploring their cage, which is fascinating to watch. They are soft to the touch, with dense, rabbit-like fur. They seem to have good memories.
  There are generally two different temperaments for STO:
Friendly - Personable, docile, friendly and cuddly. These STO enjoy interaction – cuddling in a pouch around your neck, climbing on your shirt and clothes, sitting on your shoulder, curling up in your shirtsleeve. Calm, friendly STO may climb out of their nest box to come see you if they hear you coming. My opossum comes out of his nest in the morning and watches me get ready. He climbs on the bars near me to try to get near me. I had one STO who would climb up to his “treat” area and whicker softly at me when he wanted a treat. One man’s opossum would let himself out of his cage, and then climb up on his owner’s bed to find him. My STO will sleep for hours in a pouch around my neck or in my lap while I read or watch television, or he’ll happily climb up and down my clothes while I type at the keyboard. Friendly STO can be an absolute joy.
Skitterish - Unfortunately, some STO if un-tamed or exposed to repeated stress are not quite as friendly. They may be more timid and frightened; running away when approached and hiding in the spot that’s hardest to pull them out of. They may be nervous about or dislike being picked up or held. Others will jump and run back to their nest if startled by noise, and cower until they think you’re gone. Some STO seem naturally more timid than others, despite loving care and attempts at taming. While those STO are still enjoyable to watch, they may not be the cuddly, friendly pets you were hoping for.
My STO have been sweet and cuddly, and I've loved them. But I've heard many accounts of the skitterish, nervous STO - and while some of their owners enjoy watching them even if they don't interact much, many skitterish-STO owners give them away or sell them because they're disappointed. A lot of websites promoting short-tailed opossums as “perfect pets” gloss over the fact your STO may be nervous and not enjoy people. I think it’s important for potential owners to be aware of this. I’ve read stories from too many people who bought STO expecting a sweet, cute little pet and instead got a hissing, nipping, unhappy one – a lot of these poor animals are abandoned or given away and the owners swear off STO in disgust.
My advice is to make every effort to find a good breeder who interacts and socializes with the opossums when they are little. Try to see and interact with your STO before buying it. Minimize any traumatic stress – avoid shipping if you can. Keep in mind that while you can encourage your STO to enjoy you, you cannot force them. And some may stay timid no matter how loving you are – it’s not your fault, this is a breed that isn’t completely domesticated yet. Hopefully as the breed becomes more domesticated, the sweet and cuddliness factors will be here to stay, and gradually the disposition towards an ill-tempered nature will disappear.
There are some factors that affect sweet vs. skitterish
 Females may be more skitterish than males
 Reportedly the calmer the mother, the calmer the babies
 Repeated stress/trauma in their environment may make them hide more – for example if kept in a noisy, stressful pet store for months being poked by people
 More likely to bond nicely if handled at an early age
Physical Characteristics
 Their lifespan appears to be between 4-8 years in captivity. While many websites report 8 as the average, from what I’ve noticed most people’s seem to live until around 4.
They remain small throughout their lives, slightly larger than a gerbil. Commonly when full grown they are around 4-6 inches long (without the tail!) and weigh between 3-5 ounces. Males may be up to a quarter larger than females.
Their color is typically gray to brown – dark brown/brown on top, light yellowing under the tummy. Some breeders have introduced colors, including a rosy hue, golden or ivory. Some STO have white feet and ears. Their fur is short, thick and rabbit-like softness. The male’s coat is generally thicker than the female’s.
 Their tail is prehensile, with amazing dexterity to grip for balance and anchor while climbing. They even pick up and move their bedding material by carrying it in their tail. It is usually a dark brown color, and while it doesn’t have fur on the tail like a gerbil, it isn’t scaled like a rat’s either.
Their jaw is a triangle shape and long. They have a total of 50 tiny teeth that they will show when frightened, but generally close their mouth when they realize they aren’t being threatened. Even though they have so many teeth, they are not chewers like most rodents. Which means they can have plastic toys in their cage that don’t get chewed up! (As a gerbil owner, that’s pretty exciting. My gerbils can tear almost anything plastic apart in a matter of hours). 
They seem to have an excellent sense of smell, and will spend a great deal of time sniffing around their cage. When exploring, they often pause to sniff the air.
Their ears are very thin, delicate and sensitive to sound. Some STO have a problem with their ears shriveling when kept in low-humidity, though some breeders claim to have bred this tendency out. Their ears may sometimes appear shriveled, but actually often it is the STO who is scrunching them around to hear better.
The rear legs are longer than the front legs, and seem to stretch very dexterously when they climb on different types of terrain.
They have an opposable toe on each hind foot – it is larger than the others and doesn’t have a claw. They use their back feet extensively while climbing for balance and gripping – often they will grip on with the back feet, and then explore with their front feet and nose. Their front paws are also very dexterous – they can grab crickets out of the air, and delicately grasp their food while eating.
They make many small, quiet noises. They are often very hard to hear. They generally range from quiet chittering and chirping to louder squeaks and growls.
The female has 13 nipples on her tummy that are difficult to see unless she is lactating. Her genital opening is difficult to see, and close to the anus. The male’s on the other hand have very visible, furred testicles that can be seen from behind or underneath.
Living Environment
STO come from a warm, rain forest climate. The consensus seems to be 70-80 degrees is good for them. Fewer than 70 may cause health problems, and over 80 may make the STO too hot if they’re not used to it. Some people use ceramic heating elements that warm the cage, not the nest box. Others have used warming reptile rocks. The heating lamps may disrupt sleeping.
They come from a rain forest, so humidity is appreciated. Many STO have had problems with their ears drying up and falling off from too little humidity. It is recommended by many breeders to be at least 50%, and probably not more than 90%.
STO seem to be very sensitive to noise and movement, as well as smells. I try to keep them in a quiet location where they won’t be disturbed constantly by sounds or smells.  
There are a few different options, including glass aquariums, wire cages and plastic tub/storage containers. Here are some pros and cons:
Many people like to use glass aquariums for their STO. They are economical to purchase. The aquariums contain odors, and do not need to be changed as frequently as wire cages. Be sure to cover the aquarium with a lid – some STO are escape artists. Often the STO will “flip” up to the ceiling and walk around on it upside down – it’s hard to describe, but an absolute joy to watch! The glass aquariums generally retain heat and moisture more evenly than open-air wire cages, and there usually isn’t a problem with drafts.
These are my favorites. STO enjoy climbing on the sides of the cage, which can entertain them and give them exercise. Several levels in the cage can provide more room for toys, food dishes and nesting areas. STO are very clean and like to nest as far away from their litter area as possible – a wire cage with a level near the top lets them sleep farther away from their bathroom than glass tanks allow. I personally think that STO can interact with you more in wire cages, because they can come out, smell you, and climb towards you. My STO likes to climb as close to me as he can get and then sort of rattle the bars until I come over to pay attention to him, which is very cute! On the downside, the fancy wire cages are often more expensive than glass. Because the cage is open to the air you can smell them more and may want to change the cage bedding more often. Also, the temperature and humidity can fluctuate more for the STO…and be sure to keep them out of drafts! Some people feel that the STO may feel safer and more protected in a glass cage because they don’t hear all the outside noises as much, while others contend that hearing outside noises gets them more used to noises and less skitterish
I’ve heard of a few people who use these – like big Tupperware containers - but frankly they don’t sound like a fun way to keep a pet. How can you enjoy your pet if you can’t see them? But, if you really want to keep them in a container, I’ve seen the advice that it be at least 2’x1’x1’ and with plenty of vent holes.
The size should be no smaller than 10 gallons per STO. The larger the size, the more room there is for toys, nests, food and bathroom. On the other hand, there is some anecdotal suggestion that the more horizontal room a STO has to run in, the more skitterish/fast they may become and STO in smaller cages may be tamer. Personally, I prefer wire cages as tall as I can reasonably get them. The opossums seem to enjoy the extra climbing room. A cage for breeding opossums should be large enough that both STO can get away from each other if they need to instead of fighting.
Make sure to have a lid on whatever housing you have. The lid should lock down preferably. You can use a heavy object on top of part of the lid to hold it down, if necessary. Some STO are more inclined towards escape than others.  
Housing Contents
As usual, there are warnings against cedar bedding. Most people seem to agree that it can cause respiratory problems - be sure only to use in well-ventilated wire cages. Also, some people caution against pine – but I’ve seen debates about it. Both cedar and pine bedding may cause STO to lose fur around their rump that grows back if switched to different bedding. Other types of bedding are Carefresh (my favorite – it’s not as dusty as aspen) and aspen. An exotic pet store online sells Eucalyptus bedding, which sounds interesting but I don’t know anything about it.
STO generally pick one area of their cage to use as a bathroom. It’s often the farthest corner from their sleeping area. Females are reportedly more tidy/fastidious about always using the same area than males.
Because they usually use one place for the bathroom, it can be easy to litter train them – or at the very least, keep their area cleaner. Wait a few days after their cage has been cleaned and observe which area they go to the bathroom in most often. If you fill a small dish with some shavings and a couple of their bathroom “samples” they will generally get the idea and go to the bathroom in it. It can then be cleaned out daily. Some people use regular bedding shavings for the litter box, others use recycled paper pellets or kitty litter (which may be dusty and clump to their bodies). My STO have unfortunately tended to use their wheel as a bathroom, so I just keep a little tray underneath it and empty as necessary.
They use their nest box for sleeping and hiding. They prefer dark and enclosed. It is generally said they prefer completely solid nest boxes that they have to burrow from underneath to get into, but I haven’t tried that kind yet. Some people use:
 Plastic hamster houses
 Lovebird/finch/bird nests
 Emptied margarine containers with holes cut in the side
 Wood rodent houses
 Thin flowerpots
 Plastic dog food dish upside down
I have had good luck with the plastic hamster houses. I like a compromise that gives them darkness, but also has a way for me to open it so I can take them out. My STO love to sleep in their nest box all day, then emerge at night to play. It is said the security of the nest box is VERY important for females to breed successfully – they may not breed if they don’t feel safe enough.
Short-tailed opossums weave very elaborate nests. They seem to grab the nesting material with their teeth, then push it back under their tummies. Then they “kick” the material back into their tail, which they wrap around the nesting stuff. Then they take it into their nests and arrange it. It’s truly a neat thing to watch. They will pack as much fluff into their nest box as possumly possible! People generally provide their STO with either strips of paper, white paper towel, toilet paper, tissue, hay or cotton batting. I usually use paper towel or toilet paper – they seem to appreciate both.
There is 100% certainty the STO has access to water using a water bowl, however some STO will use the water bowl as a bathroom (not very hygienic to drink out of after that!) and so requires constant changing. Also, be certain not to use water bowls with babies until they are large enough to avoid drowning!
While most STO owners use a water bottle, there are problems to be aware of. Short-tailed opossum jaws are weak, and their long tongues can sometimes make the balls in water bottles stick. So if using a water bottle, the owner needs to make sure to tap on it to make sure water is flowing, or be sure to observe that the STO is actually drinking. Here are some pros and cons:
 Ball Bottles – These are usually plastic, with a ball at the end. Their tongues can make the ball stick.
 Tube Bottle – Usually made of glass. May not work well, often release too much water and make a mess.
Some STO owners swear by ball bottles, other STO owners swear by tubes. I personally prefer ball-bottles. You may want to try both until you see which one you and your STO prefer. 
As an additional note, when babies are still transitioning to regular food, I like to provide a (shallow!) water dish and a water bottle, until I’ve watched the baby drink from the bottle repeatedly and gets the hang of it.
I think a wheel is practically indispensable! Almost all STO adore their wheel. My first STO would run up to 8 miles a night in his wheel! Frequently they will spend most of the night running in the wheel. (Squeaky/noisy wheels can be gentled with a drop of olive oil or Vaseline). One especially nice thing is that because opossums don’t chew like rodents, you can get wheels made of plastic or wood and the opossum won’t destroy them. There are several types of wheels to choose from, each with pros and cons:
 Regular wire wheel – These are the standard-sold gerbil/hamster wheels. They are inexpensive, hook on well to metal cages and are easily cleanable. If the STO uses it for a bathroom it falls to the bottom of the cage and doesn’t get really, really gross the way some other types get. Some people worry about health risks, that they may hurt their feet or limbs from either falling through the wires, or getting stuck in the axle/spokes. To be honest, this is the kind of wheel I use. My STO and gerbils have never had a problem with them. I’ve only heard of the tail/feet getting stuck rumors – never have I known anyone that it happened to. Not to say it’s not a risk, mind you – I’m just saying mine have been fine.
 Square mesh wheels – These have some great STO advantages. They can grip onto the mesh with their little feet and let themselves flip around in circles. They can leap onto it from the outside of the wheel and hang on. It’s incredibly fun to watch, and because there are fewer gaps it may be safer for them. The downsides are that they are often too big to comfortably fit in the cages, and feces don’t fall through the mesh as much – they can get stuck, or mush around onto it. It’s not a pleasant mess.
 Completely plastic all the way around – I’ve heard these are good for safety reasons, and they often come with wire cages or small animal setups. But I can imagine they would be really gross covered in feces and urine. Also they generally seem a bit small, but I’m sure larger sizes are available.
 Wodent Wheels – I’ve heard good things about them, but haven’t personally tried them.
STO like functional climbing material that they can use to explore their cage with climbing and jumping. These include:
 Stationary parrot ladders
 Snap-on cage ladders
My STO particularly appreciate arrangements where they can leap off things onto their wheel from the outside. I had one STO who would run on the OUTSIDE of his wheel by holding onto a platform ledge with his tail! I’ve noticed they do not seem to like moving climbing bird toys. And if the platforms/branches/ladders are placed somewhere illogical (as in, it doesn’t help them go anywhere or do anything specific), they may ignore it.
Hiding toys are sometimes appreciated, including hamster-house or wooden house structures, boxes.
A scared STO will open his mouth and show you his teeth when he is afraid. If you let them smell your hand, they will usually close their mouth. Or even touch them anyway … they probably won’t bite (mine never have) and it might not hurt all that much even if they do. The teeth look scary but they aren’t much of a threat! They have very weak jaws compared to rodents, and their teeth are designed for painful gnawing and grasping. Even well-tamed opossums will often open their mouths when you first put your hand in – it’s probably an instinctive prey animal reaction to your size and movement. Also, the open-mouth-showing-teeth reaction is common if you have just woken up the opossum and he isn’t quite awake or aware of his surroundings yet.
Worth noting is some STO become very scared or panicked if a shadow falls on them. You can minimize this reaction by strategically placing their cage so your shadow falls away from it.
Some STO do have a tendency to bite. I think this tendency may be avoided by a lot of bonding and taming when the STO is young. The inciting factor for some STO to bite is if they’re startled awake and haven’t recognized you yet. Un-tamed STO are far more likely to bite than tame, docile STO. I have been bitten under two circumstances – and neither type of bite hurt much! Once was when my hands have smelled strongly like food…the opossum will sniff me, look at me, look VERY confused, and then nibble gently to check if I am, indeed food. They’ve even given me a confused look that seems to say, “You’re normally NOT food, but you sure smell like it…I better check.” (Pardon my anthropomorphizing!). And once I was accidentally much harder on accident – the opossum was aiming for a mealworm in my hand but missed and got a finger. It felt very initially sharp, but not very painful after that. Serious gerbil bites feel MUCH worse.
STO are very clean little creatures, almost like a miniature cat. They lick themselves clean, groom often and comb their fur with their fingers. They lick their hands then rub the hands on their fur. They lick their hind feet in a very comical, flexible position that is fun to watch. They will do this ritual after every meal, or even several times during the meal. Sometimes they will stop in the middle of their playing or exploring to groom. When my STO are snuggled in a pouch or towel in my lap, when they curl up to sleep they will often groom themselves first – and sometimes groom my hand if it’s nearby!
They produce a somewhat of a low-key, musky odor in their cage from their scent-marking. Especially noticeable is their bedding may smell of that odor. However, they themselves do not have a smell if you take them out of their cage. I would describe them as having slightly more smell than a gerbil, but a lot LESS smell than mice or rats. STO are reportedly very comforted by their own smell – when cleaning their cage, be sure to leave some of the old bedding in their cage.
Their habits are very clean for such a small creature. Males are reportedly less picky about where they go to the bathroom than females (Big surprise! Heh!). They generally choose one corner to use as a bathroom, as far from their nest as they can. Litter training can be made easy because of this. Both of my STO have chosen to use their wheel as a bathroom, which is kind of gross. But the wheel cleans easily, and usually it just falls through to a dish I keep underneath the wheel.
This brings up an important point that many websites about STO do not mention. Because the opossums prefer to “go” as far away from their nest as possible, some STO view coming out of the cage as an excuse to go to the bathroom. While not all STO do this, some may really enjoy going to the bathroom after you let them out to play. I usually just keep a packet of wet wipes near the cage/play area, and also when I first brought the STO out of his cage I would let him climb around on a towel first until he went to the bathroom.
Another not-so-nice subject is that some STO that are timid may go to the bathroom when they are afraid – which may mean every time you pick them up. Again, I’d suggest using a package of wet wipes in the area or picking them up and putting them in a towel. This may sound gross, but it’s pretty easy to adjust to. It’s good to know this kind of information BEFORE you buy your opossum – be aware it may happen!
Generally, STO will sleep during the day and be active at night. However many opossums are willing to wake up and be active whenever you choose to play with them (or if there is food). Most of their eating and exercising is done in the evening, so I usually put fresh food in the cage only at night so the food is fresh. One thing that is nice about their sleeping during the day is that if you want to just cuddle with them, if you take them out during the day and put them in a dark warm pouch or towel they will be happy to curl up and sleep while you watch TV.
While many people have had problems with escaping STO, I have personally not had trouble with mine. In fact, on a few nights I accidentally left the top of the wire cage open. In the morning my STO was still in his cage. I’m still not certain if he didn't notice, or did notice but didn't want to leave, or got out, climbed around, and then went back into the cage knowing that’s where he sleeps and gets fed. I’ve often seen him climbing around the top at night, so I think he may have investigated, but then gone right back in to his cozy nest. By the way – don’t assume this is the way most opossums are. I’ve heard many stories of STO owners who have spent days trying to lure their opossum back to its cage. Some owners swear their smart little STO noticed an escape method, but waited until everyone was gone before using it. So you may not want to take any chances! Some suggestions to prevent escapes are that you don’t turn your back on an open cage, and secure the lid or doors to their cage.
A favored method is leaving their cage open on the ground so they can climb back in. Or, their nest box can be left out on the floor, or a pouch they like to sleep in. Some owners can lure with mealworms or favorite food. Others have used live small animal traps – but I haven’t tried this, and I’m not a vet so I don’t know if it’s safe to do or not.

The one thing almost all STO have in common about animals is that they will view any animal smaller than a rabbit as potential prey and may try to attack it. Mice, rats and gerbils they will definitely attempt to kill whenever possible. One STO managed to catch and kill a gerbil just from reaching through the bars of its wire cage! So watch out with small critters. Be aware! Keep your other small animals away.
STO are very individual little creatures though…their reactions to larger animals may vary considerably. Some people have reported their STO is afraid of cats/dogs. Other STO seem to enjoy playing with them – for example, rolling over and “butting” into a cat if the STO is inside one of the plastic run-around balls. Another person’s opossum liked riding around on the back of the family dog and climbing on his fur. Other STO may try to attack cats or dogs even though they’re huge in comparison. So be careful with your STO around larger animals until you know how they will react.  

Many short-tailed opossums can be trained and tamed into being sweet, affectionate pets that like attention.  Start bonding as young as possible. 3-4 months is a good age.
Here are some ideas on how to tame and bond with your opossum:
 Let your opossum get used to smelling your hand
 Scratch or pet his back gently while in the cage
 Wear long sleeves when putting your hands in the cage, a curious STO can climb more easily up your arm
 They often enjoy climbing around on your shirt
 Be sure to handle regularly, so they don’t revert to being timid
 If your opossum is sleepy (usually during the day), put him in a towel or a pouch (like the glider bonding pouches) and keep it on your lap. Put some of his nesting fluff inside with him. He may settle down to sleep for a while.
 While your opossum is sleeping in a pouch or towel or blanket in your lap, put your hand around him to let him get used to your smell. He may want to snuggle into your hand for sleeping, especially if it’s warm.
 A good time to try to play is in the evening when the STO is waking up – this is when they’ll be more likely to climb around on you
 Or, you may prefer handling them during the day when they’re sleepy
 Some people will sit (fully clothed) in the bathtub with their STO. That way the STO can climb all over your body and you don’t have to worry about them escaping.
 Some STO get freaked out if you walk around while holding them, others enjoy it. See what your STO prefers.
 Be careful about trying to hand-feed treats like mealworms or waxworms – your fingers then might smell like food, and wiggle enticingly like a mealworm! They might try nibbling on you.
Some final thoughts: Sometimes they won’t want to be handled no matter what – be sensitive to your STO’s mood. Keep an eye out for your opossum suddenly becoming agitated and running around your body and lifting his tail – he may need to go to the bathroom. Keep an eye on your opossum while playing to make sure he doesn’t leap onto the floor or other surfaces.  


This page was created on 08/27/04