The Virginia opossum (Didelphis virginiana) is the only marsupial found north of Mexico. This animal exhibits a rapid, high-volume breeding strategy that differs greatly from placental mammals. Understanding their reproduction is central to grasping how this species has successfully expanded its range. While the number of young produced is high, the number that survive is determined by strict biological limitations.
Opossum Litter Size and Frequency
A female opossum can give birth to a large number of young in a single litter, typically ranging from four to 25 infants. However, the average number of young that successfully attach and survive in the pouch is much lower, often between seven and nine. This discrepancy highlights the significant mortality event that immediately follows birth.
The frequency of litters depends heavily on the animal’s location and climate. In colder, northern regions, a female may produce only one litter per year. In warmer southern climates, females can produce up to three litters annually. The reproductive season generally spans from February to September.
The Journey to the Pouch
The opossum’s reproductive strategy begins with an extremely short gestation period, lasting only 12 to 14 days. This brief period means the young, known as joeys, are born in an underdeveloped state. At birth, each joey is altricial, hairless, blind, and weighs only 0.13 to 0.20 grams, roughly the size of a honey bee.
The newborn joeys must then undertake a difficult, unassisted journey from the birth canal to the mother’s abdominal pouch, or marsupium. Although they are embryonic, their front limbs are well-developed and muscular, which they use to climb through the mother’s fur. Many young do not survive this perilous trip, failing to locate the pouch opening.
The ultimate limiting factor on litter survival is the number of teats within the pouch, typically 13 in total. Each joey that successfully completes the climb must secure one of these teats to survive. The teat swells upon attachment, anchoring the infant in place to nurse. If more young arrive than there are functional teats available, the excess infants will not survive.
Development and Independence
Once securely attached to a teat, the joeys remain fixed in the pouch for an extended period. They nurse continuously and stay latched for approximately 50 to 70 days. During this time, they grow substantially, and their eyes begin to open around 55 to 70 days of age.
As the young grow and reach about two months old, they become too large for the pouch. They begin to emerge and venture out for short periods. Soon after, the young climb onto the mother’s back, clinging tightly to her fur as she moves and forages. This phase lasts until they are nearly independent.
The young opossums are weaned and begin to disperse around 95 to 105 days after birth. At this point, they are fully self-sufficient and begin their solitary life.