The mite, Varroa destructor, is the single most damaging pest of European honey bees (Apis mellifera) worldwide. While it has been present in the mainland U.S. since 1987, it did not arrive to Oahu until 2007, and soon after Hawai'i island in 2008. Current Hawai'i state laws that restrict the movement of honey bees and used equipment between the islands contributes to the Varroa-free status of all remaining islands for the time being. This pest is native to Asia, where it parasitizes its natural host, Apis cerana, or the Asian honey bee. The mite itself is small as far as mites, go, but is the largest parasite in the world when considered in relation to the size of its host! This incredibly well adapted bee parasite has a flattened body to fit between the exoskeleton segments of the honey bees to feed, and hairy claws allowing them to grip bee hairs. They feed on the fat body of honey bee adults and pupae, which weakens their immune systems and transmits a number of harmful viruses.
The mites move between bees within colonies when the bees pass by each other, and move to other colonies during robbing and drifting. This is why it is so important to monitor for and control mites in your colonies – it 
isn’t just about taking care of your bees, but being a good steward for your neighbor’s bees too. To reproduce, the female mite leaves her adult host and enters a brood cell before the bees seal it. While they may enter worker or drone cells, they are more attracted to drone cells. The female lays her eggs on the developing honey bee pupa, which hatch and continue feeding on the pupa. They leave the cell when the adult bee emerges, and move to infect other developing brood. On average, a female can produce one offspring per worker bee and two per drone since they take longer to develop. When you consider that honey bees can rear brood year round in Hawaii, this means that Varroa populations can increase 800 fold in a single year! Consistent monitoring is therefore essential!
The most accurate way to conduct a Varroa mite count of a hive is using the alcohol shake method. An instructional video for how to conduct an alcohol shake mite count can be found here.