|Rufus toe-biting - Cradle Mountain, Tasmania 8/9/2008|
I haven't worked out what the motivation for this is.
The majority will advance menacingly towards a person's foot, lightly nip at the big toe then run away. Some, however, will merely sniff at a toe. Very few will bite hard. Some possums never toe-bite at all. Ginger, our first possum, was like this. She would occasionally climb a person's leg, but never toe-bite.
Here's Kiki getting in a bit of a nip recently.
|Kiki Toe-biting 31/10/2012|
Here's Fifi and Svejk (as a baby) gently nibbling toes. They seem more curious than anything.
|Fifi Toe-biting 30/11/2009|
|Svejk Toe-biting 7/5/2007 [Photo by Xesce]|
Zorba, on the other hand, is a little more fierce.
|Zorba Toe-biting 11/12/2010|
Whereas Leena (who was otherwise always gentle and good-natured towards humans) looks absolutely crazed.
|Leena Toe-biting 26/2/2009|
|Leena Toe-biting 26/2/2009|
Mike Archer (who was at the time head of the Australian Museum in Canberra) mentioned the following in an article which explored (amongst other things) the idea of keeping Australian wildlife as pets:
"Although I have also had Swamp Wallabies (Wallabia bicolor), Nailtail Wallabies (Onychogalea unguifera), Rufous Bettongs (Bettongia rufescens) and Brushtail Possums (Trichosurus vulpecula) as house companions, each had a downside. [...] Brushtail Possums, while great as youngsters, could not resist nibbling toes when they became adult. Each, however, would have been fine in large, suitable backyards, or as visitors in the house, able to live outside."Incidentally, this article is interesting and thought-provoking and worth a read if you're interested in conservation.
An information leaflet from Magnetic Island suggests (but without providing any evidence) that toe-biting is a begging behavior.
"Some Magnetic Island possums, if used to humans, have a particular 'toe biting' behaviour. If a possum approaches your bare, sandled or thonged feet it is best to back off as they may gently or not so gently bite the big toe. It is a behaviour associated with begging and it is best not to encouraged [sic] as they may break the skin."
This explanation makes sense to a degree. Possums in city parks will often menace people in this way to extort food off them. However, I don't think this is the full story; possums also seem to toe-bite in situations where there is no food reward for doing so.
For instance, a guy in New Zealand relates a humorous story
In brief, a possum was entering the kitchen of one his friends at night to nibble on fruit. As this was in New Zealand where the brushtail possum is an introduced pest, he planned to capture (and apparently kill) this possum and therefore bunked down on a nearby couch to wait in ambush.
The cheeky possum then entered the kitchen again, and, rather than dining on fruit, sneaked up on the guy from behind and bit him hard on the toe.
I'm glad to report that the possum escaped death and in the end was merely flung out of the door into the night.
Anyway, the point is that it's very hard to reconcile this story with the theory that toe-biting is a begging behavior.