http://www.australiangeographic.com.au/journal/drop-bears-prefer-travellers-says-study.htm
Other studies have indicated that by-products of the interaction between chemicals found in vegemite and those found in human sweat repel drop bears (Honeydew 2003). Most Australians and immigrants who have lived in Australia for long periods of time tend to eat vegemite consistently (usually at least once a day), so exuding these chemicals through their skin permanently, and are thus protected.
Isn't that Nibs?