Nothing infuriates my Labrador retriever quite like a cheeky opossum (Didelphis virginiana) in the backyard, or a spooked one running off to hide under a shed or in a rocky embankment in the park. She will give chase if possible, but if the opossum turns to hiss and bare its teeth, she’ll beat a hasty retreat. Over the Christmas break, my Labbie was obsessed with the scent and pursuit of an unidentified critter in my parents’ suburban backyard; my father later trapped (and released in a wooded area along a bayou) the mystery animal, which turned out to be an opossum. That opossum fled each time my dog caught its scent and gave chase (I’ve never seen one “play possum”), and truth be told, her “encounter” with brisket and ham scraps, purloined from the garbage, was much more traumatic (and costly).
Opossum, pen sketch from my nature journal. Note that I remembered the species name incorrectly; D. marsupialis is found in Central and South America.
Opossums are nocturnal, and frequently encountered in suburban and urban areas of the US after sunset, and before dawn. This marsupial was introduced to the West Coast during the First Depression, perhaps as a food source (ugh), and has become well-established west of the Rockies, beyond its native range in the eastern US. In addition to the nuisances created by raiding garbage cans, household breaking and entering, roadkill messes, and skirmishes with dogs and cats, opossums can also harbor parasites that may cause human disease. Typhus-like rickettsiae (ELB agent) were found in the spleens of opossums in Los Angeles county, CA; opossum fleas were also infected with the ELB agent, or with Rickettsia typhi. The ELB agent, also identified in cat fleas, was thought to be responsible for mild cases of human murine typhus in the Los Angeles area (Williams et al., 1992). Infected cat fleas and opossums were confirmed to be probable reservoirs for the ELB agent, as well as an explanation for the persistence of human murine typhus in southern Texas (Schriefer et al., 1994). One in four opossums captured in urban areas of Caracas, Venezuela, was infected with trypanosomes, and these animals may be a primary reservoir for Trypanosoma cruzi, the causative agent of Chagas’ disease (Herrera and Urdaneta-Morales, 1992). Interestingly, opossums are fairly resistant to rabies infection, perhaps because of their lower body temperature.
Another common sight on suburban walks in this season: tallow tree berries
Herrera L and Urdaneta-Morales S (1992) Didelphis marsupialis: a primary reservoir of Trypanosoma cruzi in urban areas of Caracas, Venezuela. Ann Trop Med Parasitol 86, 607-612.
Schriefer ME, Sacci JB, Taylor JP, et al. (1994) Murine typhus: updated roles of multiple urban components and a second typhuslike Rickettsia. J Med Entomol 31, 681-685.
Williams SG, Sacci JB, Schriefer ME, et al. (1992) Typhus and typhuslike rickettsiae associated with opossums and their fleas in Los Angeles County, California. J Clin Microbiol 30, 1758-1762.