The yellow crazy ant (Anoplolepis gracilipes) is a species of ant, introduced accidentally to northern Australia and Christmas Island in the Indian Ocean, that has wreaked ecological damage in both locations. It is colloquially called “crazy” because of its erratic movements when disturbed, with its long legs and antennae making it one of the largest invasive ant species in the world.
Like several other invasive ants, such as the red imported fire ant (Solenopsis invicta), the big-headed ant (Pheidole megacephala), the little fire ant (Wasmannia auropunctata), and the Argentine ant (Linepithema humile), this is a “tramp ant”, a species that easily becomes established and dominant in new habitat due to traits such as aggression toward other ant species, little aggression toward members of its own species, efficient recruitment, and large colony size.
Also known as the long-legged ant or Maldive ant, it is on a list of “One Hundred of the World’s Worst Invasive Alien Species” formulated by the International Union for Conservation of Nature (IUCN). It has invaded ecosystems from Hawaii to Seychelles, and formed supercolonies on Christmas Island in the Indian Ocean.