August 3rd, 2010


Urban Nature Pictures 7/21: seen through the window version

This spider hides behind my rear view mirror by day, and makes a nice orb web at night. I feel bad driving to work when she's out twisting on her web. She doesn't go back behind the mirror until I pull in to work.

Last years' bumper crop of acorn resulted in a breeding boom of gray squirrels. The babies are all over the place, but since they have fur on their tails no one is calling me out to kill them.

50 More Urban Species #23 Virginia opossum; Urban Nature pictures 7/22

Virginia opossum Didelphis virginiana

South America was once an island continent, full of weird and wonderful marsupial mammals. Continental drift, changing ocean levels, and volcanic activity where Panama is now, brought North America into contact with it, and both places were changed forever. Placental mammals streamed down into South America and wiped out most of the marsupials. Some South American mammals made their way up the narrow passageway through Central America and into North America. Only the hardiest and most generalized scavengers had the stuff to compete with the North American animals. Today the Virginia Opossum is the only marsupial found in North America. (The nine-banded armadillo, a member of the strange mammal group that includes anteaters and sloths, is another creature that went north in the Great American Interchange.)

The Virginia opossum was limited to the American south at the time of European colonization. The creation of human-provided year-round shelter and food sources allowed the animal to expand further, reaching New England at about the turn of the 20th century. In another 80 years or so it reached the Canadian border. Accidental or deliberate introductions have created new populations of opossums on the west coast of North America.

The opossum can thrive in nearly any kind of habitat, and does well in urban areas where medium-sized predators tend to be scarce. Coyotes prefer not to feed on opossums if there are other prey animals around, and opossums can defend themselves convincingly against most smaller creatures. Showing 50 sharp teeth with a guttural drooling hiss, they can be scary when cornered. If they are pressed further they will perform their famous feigning death routine, fouling their fur with rank excretions from their cloaca. None of these defenses deter a speeding car, the creature an opossum is most likely to encounter on its nocturnal carrion-foraging missions. The Virginia opossum is among the most common roadkill animals across its range for these reasons.

Being marsupials, opossums have a lower body temperature than other mammals, and they subsequently seem to be unable to carry the rabies virus. In some parts of their range opossums feed largely on snakes, and are thought to be somewhat resistant to rattlesnake venom.

Their bare and prehensile tail is distinctive, and reports of cat-sized rats may be misreported opossums. In cold places, these animals will lose the tips of their tails and their naked ears to frostbite. This can be a way to identify an opossum that has lived a very long life, since most do not live past a single year. Even opossums living in captivity rarely live past three. However they can breed young, and each female can potentially raise 13 offspring--one for each nipple. The embryo-like babies crawl from cloaca to pouch and attach there until weaned.

A road-killed mother opossum may have living young still attached in her pouch. Wildlife rehabilitators have been known to successfully raise these babies. Sometimes when grown, these opossums are tame enough that they are used by wildlife educators as living ambassadors, to teach people about how strange and fascinating nature can be.

Also they like to be in paper bags.