Opossum, or Possum, the common name for a family of American marsupials. This marsupial originates from the Didelphidae family and is also recognised by the names ‘common opossum’, ‘black eared opossum’ or ‘southern opossum’. Opossums are distantly related to Australian marsupials such as kangaroos and phalangers. Although two species are found in North America, most opossums including the common opossum, live in Central and South America. (Hagman, 2003) Known as one of the world's oldest mammals, they date back more than 70 million years to the time of the dinosaurs. Didelphis marsupialis are one of 60 species of opossum in the world and the common opossum is the only marsupial living in the united States. (Missouri Department of Conservation, 2013)
The range of the common opposum stretches from eastern Mexico to north eastern Argentina. It maintains a stable population, however, it is sometimes hunted for its meat in poorer parts of the world. Its range is limited by high elevation and dry environments. (Redford, et al. 1992) The common opossum is native to the following countries: Argentina; Belize; Bolivia, Plurinational States of; Brazil; Colombia; Costa Rica; Ecuador; El Salvador; French Guiana; Guatemala; Guyana; Honduras; Mexico; Nicaragua; Panama; Paraguay; Peru; Suriname; Trinidad and Tobago; Venezuela (Brito, et al. 2008)
The common opossum is about the size of a large house cat and weighs between 4-12 pounds. In most cases, females are smaller than males. It possesses an elongated head with a slender snout that ends with a pink nose. (Cerqueira, et al. 2000) These mammals have sharp claws, long whiskers and a long, prehensile tail which enables the opossum to hang from trees and support its own weight. This tail has been known to have other functions such as for balance when in motion and to transport materials by wrapping it around the object(s). (Hagmann, 2003)They have large mouths producing so much saliva that they it drips from their mouth a considerable amount of the time. Southern opossums tend to display more dark guard hairs than opossums living in northern parts of America, and so are characterised by dark ears and a dark coat. (Krause, 2006)
These terrestrial animals can be found in rainforest, subtropical forest and near human settlement where they have access to garbage. They are form primarily on land but their movements have also been recorded on trees. As opportunistic feeders, they often shift home ranges in response to amount of available resources. (Hagmann, 2003) They cannot live in extremely arid zones or at high altitudes above 2,232m. The females make a nest of leaves in a tree burrow. It has been reported that the common opossum can live for up to 7 years in captivity but its life expectancy in the wild is around 2 years which makes them one of the most short lived animals in the world for their size. (Krause, 2006)
The Didelphis marsupialis feeds primarily on earthworms, beetles and grasshoppers all year round. Its diet varies seasonally, consuming more mammals and birds in the dry season and more fruit and snakes during the wet season. Their apparent immunity to the venom of particular rattlesnakes aids their consumption of this reptile. (Hagmann, 2003)This is because they possess a particular proteinase inhibitors in their blood which binds to these snake venoms and neutralise their toxins. the common opossum finds food by walking at a slow speed and move their head n a side to side motion to ensure they smell as much of the ground around them as possible. If the food is too large the opossum may hold the food down with its front feet as it eats it. (Tyndale-Biscoe, et al. 2005)
Ocelots, jaguarundis and harpy eagles are amongst the organisms known to predate the common opossum. To deter predators the marsupial shows its teeth in an aggressive manner. In addition, it may start to drool which helps to make the opossum look infectious and therefore unappetising (Tyndale-Biscoe, et al. 2005). However, the opossum is most commonly known to adopt a passive defensive tactic known as ‘playing opposum’ or ‘playing dead’. This condition may last less than a minute or up to six hours. To aid this impression of death, the marsupial secretes a substance from its anus which creates the odour of a dead animal. They will lie on their side with their tail rolled up, eyes and mouth open and paws closed to a certain degree. (Parker, 1990) Faking their death increases the chance of a predator walking away or discontinuing its attack. In addition, this catatonic state helps to confuse predators as they lose the visual stimulus of motion and provides the opossum with a better chance of running to safety. (Nowak, 2005)
The common opossum is considered a shy, solitary animal that will hold down a territory for a half a year to a year before venturing somewhere else. Aggressive behaviour is common and is characterised by baring of the teeth out stretched forelimbs and the head high in the air. (Hagmann, 2003) Males make a clicking sound with their mouths to attract females. (Tyndale-Biscoe, et al. 2005)
Male opossums compete for reproductive females but when resources are limited, these animals choose not to mate. During the breeding season is the only time in which these animals are found in the presence of each other. The female esterous cycle is between 25-32 days and females usually become able to reproduce after 6 to 7 months. There is evidence to suggest that the breeding season and size of litter depends on latitude (Hagmann, 2003). Newborns are very small in size and must find their way to their mothers’ marsupian (or pouch). The pouch may have up to 13 teats on which the young opossums suckle in order to obtain nourishment, and has a warm, woolly interior to provide the young with warmth. They can only move with their forelegs as their hind legs are not developed enough, and possess well developed claws that enable them to climb into this pouch. There is a high mortality rate at this time in development as the mother possesses only nine nipples and often gives birth to more than nine young (Krause, et al. 2006).
There are two theories as to the way in which newborns reach their mothers marsupian: by smell and through gravity. According to the first theory, the young follow a trail of saliva made by the mother directing them to the opening of the pouch. The second theory suggests the teats swell at the tips when they reach the nipple to prevent them falling off. (Einsberg, 1989) The mortality rate is significantly lower once the young are established in their mothers’ pouch and remain attached here for 50 days. The composition of marsupial milk varies throughout the stages of lactation, production and concentration increasing as time goes on (Krause, et al. 2006).
A study has suggested that the sex ratio in offspring can be determined by the amount of resources delivered by the mother Didelphis marsupialis: a female who provides enough resources is predisposed to have mostly male young and when supplies are low, she is more likely to produce female young (Einsberg, 1989).
Relationship to Man
They are brilliant scavengers and are important in keeping insect and rodent populations in check. They are also important in seed dispersal as some seeds which they consume pass through undigested. The common opossum acts as an indicator species as I is found in areas where the environment is healthy. (Krause, 2006)
Despite living very close to humans, they rarely cause any serious problems hoever they have been identified as the host species for parasiteTrypanosoma cruzi, which is the source for the human illness known as Chagas Disease (Dean, et al. 1984) . Evidence suggests the opossum also hosts a protozoan known as Sacrococystis neurona which is though o be associated in the development of a serious neurological disease in horses.
Hagmann, K. (2003). "Didelphis marsupialis" (On-line), Animal Diversity Web. Accessed October 2013 Nowak, R. M. (2005). Walker’s Marsupials of the World. Baltimore: The Johns Hopkins University Press. Tyndale-Biscoe, H. (2005). Life of Marsupials. Collingwood, Australia: CSIRO Publishers. Didelphis marsupialis (Common Opossum or Manicou) Brito, D., Astua de Moraes, D., Lew, D., Soriano, P., Emmons, L., Cuarón, A. D., Helgen, K., Reid, R. & Vazquez, E. (2008). Didelphis marsupialis. In: IUCN 2008. IUCN Red List of Threatened Species. Last accessed October 2013
Deane, M.P., Lenzi, H.L., Jansen, A. (1984) Trypanosoma Cruzi: Vertebrate and Invertebrate Cycles in the same mammal host, the opossum Didelphis Marsupialis. Mem. Inst. Ostwald Cruz, Rio de Janeiro, 79(4), 513-515.
Krause, W.J. & Krause, W.A (2006). The Opossum: Its Amazing Story. Columbia, Missouri: School of Medicine, University of Missouri,. 28-38 & 73-78.
Missouri Department of Conservation. (2013). Opossum(Didelphis marsupialis). Available: http://www.news-leader.com/article/20130228/LIFE06/302280070/?nclick_check=1#. Last accessed October 2013.
Parker, (1990). Grzimek's Encyclopedia of Mammals. New York: McGraw Hill Redford, K., J. Eisenberg. 1992. Mammals of the Neotropics, the Southern Cone. Chicago: University of Chicago Press.
Eisenberg, J., K. Redford. 1989. Mammals of the Neotropics, the Northern Neotropics. Chicago: University of Chicago Press.
Cerqueira, R., B. Lemos. 2000. Morphometric differentiation between Neotropical black-eared opossums and *D. aurita*. Mammalia, 64: 319-327.
- Didelphis marsupialis Linnaeus, 1758
- Type locality: "America"
- Didelphis marsupialis in Mammal Species of the World.
Wilson, D. E. & Reeder, D. M. (eds.) (2005). Mammal Species of the World. A Taxonomic and Geographic Reference. Third edition. ISBN 0801882214
- Linnaeus, C. 1758: Systema Naturae per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis, Tomus I. Editio decima, reformata. Holmiæ: impensis direct. Laurentii Salvii. i–ii, 1–824 pp doi: 10.5962/bhl.title.542: page 54.
- IUCN: Didelphis marsupialis Linnaeus, 1758 (Least Concern)