It has been estimated that 10-15 million red crabs, or
one-quarter to one-third of the entire population, have been
killed by this invasive ant over the last several years across
c. 25 km2 of rain forest (P. Green, unpubl. data). Crazy ants
kill red crabs through sheer force of numbers and constant
activity, overwhelming the crabs by spraying formic acid
over their eyes and mouthparts. Although the exact
physiological mechanism by which formic acid kills crabs
is unknown, death is usually swift and occurs within 48 h.
As supercolonies spread, crazy ants occupy red crab
burrows, kill and consume resident crabs, and use burrows
as nest sites. Furthermore, large numbers of red crabs are
killed in transit during their annual migration (Hicks 1985),
when migratory pathways intercept Anoplolepis supercolonies.
This effect at a distance can deplete crab populations in
areas not directly invaded by the crazy ant, setting in train
indirect effects on seedling abundance and litter decomposition.
However, this was unlikely to have affected control
plots during our study; burrow densities on these plots were
within the range reported prior to the wid