▁st ance ), ▁but ▁at ▁low ▁walking ▁spe eds ▁( 0 – 1 5   mm / s ), ▁f lies ▁are ▁more ▁likely ▁to ▁have ▁four ▁or ▁five ▁legs ▁in ▁st ance . ▁These ▁trans itions ▁may ▁help ▁to ▁optimize ▁static ▁stability . ▁Because ▁f lies ▁are ▁so ▁small , ▁in ert ial ▁forces ▁are ▁neg lig ible ▁compared ▁with ▁the ▁el astic ▁forces ▁of ▁their ▁mus cles ▁and ▁joint s ▁or ▁the ▁vis c ous ▁forces ▁of ▁the ▁surrounding ▁air . ▁ ▁In ▁addition ▁to ▁stability , ▁the ▁robust ness ▁of ▁a ▁walking ▁g ait ▁is ▁also ▁thought ▁to ▁be ▁important ▁in ▁determ ining ▁the ▁g ait ▁of ▁a ▁fly ▁at ▁a ▁particular ▁walking ▁speed . ▁Rob ust ness ▁refers ▁to ▁how ▁much ▁offset ▁in ▁the ▁timing ▁of ▁a ▁legs ▁st ance ▁can ▁be ▁toler ated ▁before ▁the ▁fly ▁becomes ▁stat ically ▁un stable . ▁For ▁instance , ▁a ▁robust ▁g ait ▁may ▁be ▁particularly ▁important ▁when ▁travers ing ▁une ven ▁terrain , ▁as ▁it ▁may ▁cause ▁unexpected ▁dis ru ptions ▁in ▁leg ▁coord ination . ▁Using ▁a ▁robust ▁g ait ▁would ▁help ▁the ▁fly ▁maintain ▁stability ▁in ▁this ▁case . ▁Anal ys es ▁suggest ▁that ▁D ros oph ila ▁may ▁exhib it ▁a ▁comprom ise ▁between ▁the ▁most ▁stable ▁and ▁most ▁robust ▁g ait ▁at ▁a ▁given ▁walking ▁speed . ▁ ▁Fl ight ▁ ▁F lies ▁fly ▁via ▁straight ▁sequences ▁of ▁movement ▁inter sp ers ed ▁by ▁rapid ▁turns ▁called ▁s acc ades . ▁During ▁these ▁turns , ▁a ▁fly