THE ANTS THAT JUMP - DIFFERENT TECHNIQUES TO TAKE-OFF

The movements that lead to take off in jumping ants has been analyzed in the three ant species, Harpegnathos saltator, Myrmecia nigrocincta and Gigantiops destructor. The total time elapsing from the beginning of a well defined intention movement to leaving the ground is for all three species 15-25 ms. Harpegnathos takes off with a speed of about 0 .7 m/s, Gigantiops with about 0.6 m/s. H. saltator leaps with its meso thoracic legs. The center of mass sits anteriorly to the insertion of the mesothoracic legs within the mesothorax. To avoid spinning during jumping, in the first phase of the leaping movement, the hind legs pus h the animal forward, then the mid legs extend very rapidly, pushing t he animal forwards/upwards. M. nigrocincta leaps by extending its meso - and metathoracic legs simultaneously. This provides enough accerelat ion to leave the ground. The leap of G. destructor is driven by kineti c energy gained from extending legs and a forward thrust of the gaster . This mechanism also appears to prevent the ant from spinning backwar ds, as the center of mass lies within the petiolus, that is posterior to the insertion points of the hind legs. In Harpegnathos and Gigantio ps, the jumping movements were also analyzed in individuals tethered a t their thoraces and suspended in air. In this way it was possible to demonstrate that the jump is a fixed action pattern that needs no sens ory feedback from forces occurring during the leap.