Acarapis woodi is a microscopic mite (about 150 microns — invisible without a microscope) that enters a honey bee's first pair of thoracic spiracles within hours of the bee's emergence, when the guard hairs are still soft. Inside the trachea — the branching breathing tubes that carry oxygen directly to the flight muscles — mites pierce the tube wall and feed on hemolymph, then lay eggs. As mite numbers build, dark scarring and physical blockage restrict airflow to the flight muscles.
Tracheal mites were long suspected in the mysterious "Isle of Wight disease" that devastated British colonies from 1904, though a firm cause wasn't confirmed until decades later. Today most commercial stock carries useful resistance, and tracheal mites rarely cause colony collapse on their own — but they still weaken bees enough to tip a marginal winter cluster over the edge.
A cutaway of a honey bee's thorax reveals Acarapis woodi mites feeding inside the tracheal breathing tubes and slowing the flow of oxygen, while a linked colony view shows how infestation spreads bee to bee.
Mite load inside a single trachea drives visible tube scarring and a slower, thinner stream of oxygen particles; across the colony, the same infestation level determines what share of bees appear dull and tremble like K-wing symptomatic bees.
Raise colony infestation and mite load to see blockage build up, switch seasons to see how reproduction speed changes, and toggle resistant stock to see hygienic behaviour push the population trend back down.
Because Acarapis woodi lives hidden inside the trachea, it can't be diagnosed by eye — beekeepers still need to dissect and examine tracheae under a microscope to confirm it.