The Varroa mite is only the size of a pin head but it is the most serious threat to the viability of the Australian honey bee industry.  The little bugger is parasitic and feeds on the blood of adult and larval honey bees. It transmits viral and other pathogens, which kill entire bee colonies. Varroa mite is a large part of the problem that has caused honey bee decline in many places around the world. 

The mite is highly invasive and has colonised the whole world relatively quickly. Varoa originated in north Asia in the 1950s and spread to Europe in the 1970s. It then spread to the USA, Southeast Asia, South America and Africa. In 2000 it turned up in New Zealand. And now, it is in Queensland. 

This fact sheet was issued by the Queensland bio security office on 21st July 2016:

      https://www.business.qld.gov.au/industry/agriculture/species/declared-pests/animals/varroa-mites

This YouTube video shows you what the tiny little things looks like and how it spreads its lethal diseases:

     https://www.youtube.com/watch?v=Nfn4jwqUqvI