Abstract: Field margin management for conservation purposes is a way to protect bothfunctional biodiversity and biodiversity per se without considerable economical loss as fieldmargins are less productive. However, the effect of width of the buffer zone on achievablebiodiversity gains has received little attention in previous studies. In this paper we report onfinding for syrphids, spiders and carabids, three taxonomic groups with different mobility, allimportant for conservation biological control. For all groups we found an effect of buffer zonewidth on their density. A buffer width of 6m was the narrowest that consistently promoted ahigher abundance or activity of arthropods within the field area (outside the hedge bottom).However, a further increase in buffer width always increased the abundance and activity ofarthropods a little more.