Brilliant mimicry

We planted a bed of mustard seed a month or so ago to keep the soil covered after harvesting a crop of potatoes. This helps to limit soil erosion over the winter and to suppress weeds. It also allows the mustard to absorb nutrients before being dug into the soil as a 'green manure'. Ideally this should occur before the plants flower. However, we couldn't resist the temptation to leave these beautiful yellow flowers to appear and the plethora of insects that have followed in search of the abundant nectar they produce. The drone, or hoverflies (Eristalis tenax), pictured here, have been particularly frequent visitors. They cleverly mimic the honey bee as a defensive strategy known as Batesian mimicry. The key difference between the two is the honey bee has two pairs of wings and the drone fly just one.