The BIGGEST fly I ever saw !

Last July while conducting my butterfly transect I encountered the biggest  fly I ever met,at first I thought it was just  an unusually large Noon day fly but it quickly became obvious that it was something else .
A visit to the reference books turned up Tachina grossa a tacnid fly,these prey on large hairy catterpillars on which they lay eggs, that hatch and burrow into the caterpillar eating it alive, leaving the vital organs till last so as not to kill it prematurely.