Is it a mouse? Is it an opossum? Meet the adorable Mexican mouse opossum (Marmosa mexicana)! Also known as zorro ratón, zorricí, or zorillo in Costa Rica, this tiny creature is about 6 inches long and weighs around 3 ounces. With males being slightly larger than females, they have a reddish-brown mouse-like appearance with a black eye mask and a long prehensile tail.

These opossums use their tails to navigate trees, as they are mainly arboreal animals that live and hunt among the branches. Their diet includes fruits and insects, and they also eat lizards, birds, mice, and bird eggs. They have a knack for raiding nests of house wrens, parrots, and woodpeckers.

Being nocturnal, they do most of their tree climbing and hunting at night. During the day, they nest in abandoned bird nests, make their own leaf nests, or, less commonly, burrow in the ground.

Other species in Costa Rica’s wild ecosystem prey on these tiny creatures, with their bones found in owl pellets and in rattlesnake stomachs. Despite their size, Mexican mouse opossums can be aggressive when threatened.

One surprising fact about these opossums is the absence of pouches. Following a short gestation, the female gives birth to 1 to 14 larvae, which cling to her and nurse for the first month of life. As they grow, they begin accompanying their mother on excursions, then can reproduce at five or six months old. However, it’s believed few Mexican mouse opossums survive past two years.

You can catch glimpses of this fascinating little creature through camera traps in trees or on the forest floor. Brief yet charming videos show their quick, mouse-like movements before they vanish from sight.

Vincent Losasso, the founder of Guanacaste Wildlife Monitoring, is a biologist who works with camera traps throughout Costa Rica. Learn more about his projects on Facebook, Instagram, or by emailing

1. Look up and into the trees: Mexican mouse opossums are mostly arboreal, so keep an eye out for them among the branches.

2. Explore at night: Since Mexican mouse opossums are nocturnal, your chances of spotting one are higher during the nighttime.

3. Listen for rustling in abandoned bird nests: During the day, Mexican mouse opossums can be found nesting in abandoned bird nests, so listen for rustling sounds when exploring potential nesting spots.

4. Keep your distance: While Mexican mouse opossums may look adorable, they can act aggressively when trapped, so it’s best to observe them from a safe distance.

5. Stay quiet and patient: Mexican mouse opossums are known for their quick movements and tendency to disappear rapidly. To increase your chances of sighting one, stay quiet and patient, waiting for any movement or rustling sounds.

6. Consider using camera traps: If you want to increase your chances of capturing footage or images of Mexican mouse opossums, try using camera traps in trees or on the forest floor.


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