Opossums are fascinating marsupials that carry their young in a pouch. If you’ve ever wondered how big a 4 month old baby opossum is, you’ve come to the right place.
If you’re short on time, a 4 month old opossum is typically about 6-8 inches long from head to rump.
In this comprehensive article, we’ll cover everything you need to know about the size of 4 month old opossums, from their weight and length to how their growth compares to adult opossums. We’ll also discuss key facts about opossum development and what impacts their size.
Typical Size of a 4 Month Old Opossum
Length
At 4 months old, an opossum is reaching adolescence and entering its rapid growth phase. The average length of a 4 month old opossum ranges from 6 to 8 inches from the tip of its nose to the base of its tail. Males tend to be on the larger end of this range. Females are typically a bit smaller.
The tail adds another 8 to 10 inches to an opossum’s length at this age. Their tails are nearly hairless, thin, and very flexible, allowing them to wrap around objects as they climb. A 4 month old opossum is about the length of a large avocado when the tail is excluded.
Weight
The average weight of a 4 month old opossum is between 250 and 350 grams. That’s about 0.5 to 0.8 pounds. Males again tend to weigh a bit more than females once they reach 4 months of age. At birth, opossums weigh just 0.13 grams on average, so they experience incredible growth in a short span of time.
An opossum this age has the weight of a large apple or orange.
Opossums gain about 2.5 grams per day after 40 days old. So a 4 month old opossum (120+ days old) will have added around 200 grams since its 2 month birthday. The rapid weight gain is fueled by their diverse omnivorous diet and fast metabolism needed to support their energetic lifestyle.
Differences Between Males and Females
There are a few key differences between male and female opossums at 4 months old:
- Males tend to be slightly larger in both length and weight compared to females of the same age.
- Males develop a stronger odor as they reach sexual maturity around 4 to 6 months old. Females emit pheromones but lack the strong musky smell.
- Males have a forked penis bone called a baculum which females lack.
- Females have a complete marsupium (pouch) for carrying babies. Males have only a rudimentary pouch.
- Males have larger canine teeth than females.
Despite some subtle physical differences, male and female opossums are quite similar in appearance at 4 months old. Both genders have the same white facial markings, hairless ears, textured greyish-white fur, long tails, hand-like paws with opposable “thumbs”, and other classic opossum features.
Personality and behavior tend to be comparable as well.
Growth Rate and Stages
Birth Size
Opossums are extremely small when they are born, often fitting in the palm of an adult human hand. Newborn baby opossums typically weigh just 0.13 ounces (4 grams) and have a body length of 0.51 inches (13 mm) without the tail. That’s about the size of a bee!
They are born hairless and with their eyes and ears closed. Their underdeveloped state makes them very vulnerable.
Key Growth Phases
Opossums grow and develop rapidly in their first 4 months while nursing in their mother’s pouch. There are some key growth phases:
- In the first week after birth, baby opossums open their eyes and their ears begin working.
- At 3-4 weeks old, they have fur and can climb into the mother’s pouch on their own.
- Between 8-13 weeks old, they venture out of the pouch but frequently return for nursing.
- By their fourth month, juvenile opossums are fully weaned off milk and forage for food on their own.
When They Reach Adult Size
Opossums reach adult size at approximately 4-6 months old. According to wildlife experts, most opossums reach full adult dimensions by 16-20 weeks of age. Male opossums tend to grow a bit larger than females. Adult males average 21 inches long (including a 9 inch tail) and 9 pounds.
Females average 19 inches (8 inch tail) and 7 pounds. The Virginia opossum is North America’s only marsupial and is about the size of a large house cat when fully grown.
Factors Affecting Size
Genetics
An opossum’s size is greatly determined by its genetics. Like other mammals, opossums inherit genes from their parents that influence their growth and development. Opossums that come from larger parents tend to grow bigger than those from smaller parents.
Additionally, some opossum subspecies just naturally grow larger or smaller based on their genetic makeup. For example, Virginia opossums typically reach sizes of 2-3 feet in length and 4-15 pounds in weight.
In contrast, common opossums of Central and South America only grow to about 1 foot long and 1-2 pounds. So genetics plays a major role in determining just how big an opossum will get.
Health and Nutrition
Number of Siblings
The number of siblings an opossum has can impact its size too. Opossums typically have very large litters of up to 20 joeys. When opossum mothers have smaller litters with fewer babies to feed, those joeys tend to get more milk and grow bigger than those in large litters who must compete for resources.
For example, an only joey in a litter may reach 5 pounds by 4 months old, while joeys with 10 siblings may only reach 2-3 pounds in the same timeframe. Fewer siblings means more nutrients to go around for each joey.
However, genetics and nutrition are still the most important factors, as joeys in small litters can still be small if they have small parents or poor diets. But littermate competition can create size differences, with less crowded joeys sometimes growing more.
Behavioral Changes with Growth
Mobility Skills
At one month old, baby opossums, called joeys, begin to open their eyes and their mobility skills start to develop. They go from crawling to walking and climbing in a short period. According to research from the Opossum Society, joeys as young as 6-7 weeks old are able to climb into their mother’s pouch on their own to nurse.
By 3-4 months old, they have the agility to start venturing out of the pouch, exploring their surroundings independently while their mother is out foraging.
Independence Levels
As juvenile opossums grow over 4 months, they depend less on their mother for survival. At one month old, joeys rely entirely on their mother’s milk. By 3-4 months of age, they start eating solid foods that their mother brings back to the den, like insects, rodents and fallen fruit.
According to OpossumSocietyUS.org, 4 month old joeys even hunt prey like mice alongside their mother. They are weaned by 5-6 months old.
An opossum mother’s supervision decreases too. At 1 month old, joeys need round-the-clock care while tucked in her pouch. By 4 months of age, they only nurse 1–2 times per day and spend more solo time outside the pouch while their mother is away.
Their survival instincts and abilities are strong enough to venture out alone even at night by 4 months old.
Interaction with Mother
The nature of interactions between 4 month old joeys and their mothers changes markedly. While 1 month old infants are carried constantly by their mother, older joeys primarily interact with their mother when nursing or during brief periods back in the den.
According to research from Utah University’s Biology Department, mother opossums even hiss or snap at 4 month old joeys to drive them off, though not aggressively.
This reduced contact prepares the 4 month old joeys for independent life. By 5-6 months old, they have matured enough physically and behaviorally to permanently separate from their mother. The joey-mother bond lasts just a few short months due to the opossum’s rapid maturation rate.
Conclusion
Now you know all about the typical size of a 4 month old opossum. A baby this age is still developing quickly but reaching a size where they gain mobility and independence. Their growth rate slows around 4 months but they still have some maturing to reach full adult dimensions.
Understanding how opossums grow and what impacts their size can help you identify healthy development if you rescue injured wildlife. Hopefully this comprehensive overview gave you all the key details about 4 month old opossum dimensions.
