Bees give life to our gardens, but over the past few decades they’ve run into a number of issues harming the population. One of the most insidious are Varroa mites. Although only 1.1 to 1.5 mm wide, enough of them can destroy a hive, which is why it’s important to control Varroa mites in the fall. 

Originally a pest of honeybees in Asia, Varroa mites  hitched rides to colonies in Africa, then to Europe. By 1987, the United States reported them. Canada and Mexico closed their borders to bees from America in an attempt to stem the infestation. Now only Australia is free of the mites, although knowing the nature of these types of things, it will most likely not be this way for long. 

Lifecycle of the Varroa mites 

Understanding their lifecycle is why we try to control Varroa mites in the fall. It all begins with an adult Varroa mite female that lays 2-5 eggs in a pre-capped larval cell. They prefer drone cells because drones take longer to hatch, which means a longer time for the larvae to feed. What’s really interesting, is the first egg she lays is always a male. (Use that little bit of trivia the next time you want to wow someone with bee knowledge.) 

As the larval mites hatch and develop, they feed upon the larvae and actually mate within the cell. By the time the bee emerges, the male mite is dead, but the females are ready to lay brood of their own. A female mite can live a couple of months and even overwinter if they tuck themselves within the scales of the honeybees’ bodies. As the bees cluster to keep the hive warm, the mites remain nice and cozy.

Why you need to control Varroa mites

Mites are endemic to a certain extent. But we must do our best to keep them in check if we want our bees to be healthy. Besides sucking the blood from larvae and adult bees, ultimately weakening them, mites are prime vectors for disease. So if the mites don’t kill them, disease very well might. 

For the past several seasons, our honeybee colonies looked terrific going into the fall. They were large hives with plenty of honey. But even when we didn’t have severe cold or harsh weather conditions, they died before real winter even hit. My thought is it’s because of the mites, which is why we’re treating them this year. 

Bees Gone Wild

Options for control

When I first starting keeping bees in 1996, about the only product available was Apistan, which are strips of a chemical treatment that you place in the hive after honey harvest. This is a very important consideration since much of what we use is not something we want in our honey! 

Instead of using the chemical method, this year we will vaporize oxalic acid to knock down the mite populations. I first learned about this from our neighbor, Dave, who bought the equipment to treat his own hives. He invited me over to watch his first treatment, and subsequently showed me the sticky board from the first hive displaying a large number of dead mites. Obviously, it works. 

There are several different methods, but the way Dave used involved a small heating unit used specifically for this purpose. This required hooking up the unit to the battery in his riding lawn mower, but other than that, it’s fairly simple and straight forward. 

He started by putting on a respirator. Although oxalic acid is a natural substance, it’s harmful if inhaled, particularly when vaporized. After smoking the bees to encourage them to go back into the hive, he measured out the oxalic acid, slid the vaporizer into the bottom of the hive, sealed the entrance, and hooked the vaporizer to the battery. After a few minutes, he removed the vaporizer, and kept the hive sealed for approximately 10 more minutes. 

Checking for mites

As I mentioned, the proof was on the sticky board. There were a lot. Dave said he will do one more treatment. This allows any of the capped brood to hatch, revealing additional Varroa mites. 

Controlling Varroa mites is an important part of honeybee husbandry. Thankfully, as knowledge and technology improve we have more options to keep our bees mite free and healthy.