A runner is basically the most junior in the department. This is an unforgiving but very useful role which involves a lot of fetching and carrying of items, driving people/props around, taking messages and relaying them to team members, looking after guests to the set, hiring of any props needed and picking up cast for appointment such as Makeup calls. Oh and most importantly of all, providing the team with a generous and never-ending supply of Tea.
Hiring a runner means that all bases will be covered; they act as an important support function to the team and speed up processes which would add time to the schedule should they not be there. They keep the busy production team afloat and make sure that they are on top of tasks that otherwise might be forgotten about in the excitement of film making. Also the Dragonfly team, like most members of the public, generally function better with tea.