Incidence and prevalence are terms commonly used in describing disease epidemiology. Incidence. Incidence is the rate of new (or newly diagnosed) cases of the disease. It is generally reported as the number of new cases occurring within a period of time (e.g., per month, per year).
Pictured: Incredible gravity-defying ant that can carry 100 times its body weight. This extraordinary image of an ant carrying 100 times its own body weight has scooped first prize in a science photography competition. The photo shows an Asian weaver ant hanging upside down on a glass-like surface and holding a 500mg weight in its jaws.
As for brain-to-body mass ratio, some small insects seem to win out. This is because of an allometric principle called Haller's Rule, in which smaller animals tend to have proportionally larger brains. Some small ants have brains about 15% of their total body weight. (See The Allometry of Brain Miniaturization in Ants by Marc A. Seid et al., Brain, Behavior, and Evolution, 2010.) In general, younger animals tend to have the largest head-to-body ratios.