The Enemy Within

So this is what all the fuss is about. The one detail about honeybees that even many non-beekeepers have heard about: Varroa or, to give it its full title, 'Varroa destructor'. A portentous name for such a mite of a thing (Do people still use that phrase? When I write it, I hear it in my Grandma's voice). Appropriate though, as it it indeed a mite, a parasitic mite, first identified as such in 1904, on Asian honeybees, Apis cerana

Sorry there is no scale; I'm rather surprised to have a picture at all with just a phone. In its longest dimension it is about 1mm. Mites are arachnids, cousins of spiders. If this one was alive, it would have eight short stumpy legs sticking out of the front, along with some mouthparts in the centre of the eight. The 'front' is the south-west in this picture - the creature is wider than it is long. Its blood-red, shiny exoskeleton makes it quite easy to see, even amongst all the bits of chewed wax on this board

Varroa reproduce by entering a brood cell, just before it is sealed and laying eggs inside the sealed cell. The eggs hatch and mother and offspring puncture the exoskeleton of the growing bee and feed from its 'fat body' (the insect equivalent of a mamalian liver), before escaping from the cell with the adult bee when it emerges, to infect other cells. This is not great for the bee but, even worse, the mite is a vector of bee viruses, particularly 'deformed wing virus'. These debilitate the bee, shorten its life, damage its learning ability and, in some cases cause the eponymous deformity. If the population of Varroa builds up in the colony, so does the virus load and the colony dies

Apis cerana is fairly tolerant of Varroa, having co-evolved with it for millions of years. It grooms itself to remove Varroa that hitch a ride on its body, and detects and evicts them from inside sealed cells. When humans took western honeybees (Apis mellifera) to Asia, the mite happily expanded on to a new host, but western bees have none of the defence mechanisms of their Asian cousins. Like native South Americans facing conquistadors with unknown tools of gunpowder, horses and western viruses, they succumbed

Varroa has now spread to western honeybees all around the globe - finally breaching even Australia's defences recently, and now spreading across that continent. It has become necessary for beekeepers to do the job that their bees cannot: control the population of Varroa in every hive. We have put a paste containing the aromatic chemical found in the Thyme plant ('Thymol') into the hive, as we do at this time every year. This irritates the mites that are hitching a ride on the worker bees, causing them to fall off and fall through the wire mesh floor of the hive. We put this board under the floor to catch what falls through - bits of chewed wax, small pearls of the Thymol gel, discarded by the bees, and the doomed Varroa, now detached from their host. Thankfully, there are mercifully few mites to be seen

What a complex biological interaction we have created: an insect, an arachnid, a mammal and a herb; our own little dance to the music of thyme