Everyone who keeps honey bees has at least heard of the parasitic mite, Varroa destructor. You can tell just by the name it isn’t going to be good. It isn’t Varroa Nicelady or Varroa Iwannaknowya. Varroa destructor. Destructor of larva, of adult bees, of your dreams of honey and well pollinated gardens.
We know about the harm varroa causes: spreading disease, weakening bees, and making colonies collapse. And we hear a lot about how to control them. But how exactly do these mites live their disgusting yet fascinating lives?
Let’s look closely at one mite, the sort you could see on one of the bees in your hive. We’ll call her Marcia. She’s in the “traveling” or phoretic stage of her life cycle. Mites like Marcia prefer feeding on nurse bees, but will occasionally “go hobo” - hitching a ride on a worker bee or drone to travel to a new hive.
Eventually, Marcia will want to settle down and start a family. She’ll scurry into the bottom of a brood cell and hide down in the brood food so no vigilant bees can spot her. When the bees cap the cell, it’s Marcia’s time to shine. First, she’ll lay an unfertilized egg - this will make her a son, a son that she’ll name Timmy. She’ll then lay a few fertilized female eggs. It’s thought that up to six eggs can be laid in worker brood, and up to seven can be squeezed into a beefy drone cell.
Marcia, the doting mother, will pierce the bee pupa just once so her baby mites, whose mouths are too puny and weak to penetrate the pupa, will be able to feed. She only makes one feeding hole, lest she cause the pupa to explode. What a gal. This feeding hole is located near an organ called the “fat body” on which the varroa feed. This would be sort of like mosquitoes sucking on your liver, if mosquitoes were the size of cats.
You’ll be happy to learn things get even more disgusting! The mites also choose one place in the cell to poop, called the “fecal accumulation site.” After the baby mites reach adulthood they start feeling amorous. So where’s an amorous mite to go when he or she wants to find a date? Why the “fecal accumulation site” of course! Romantic.
So all Marcia’s little daughters head to the fecal accumulation site to mate with their brother, Timmy. From my reading, I was unclear on whether Marcia would also mate with Timmy or if her initial mating back when Marcia was a newly matured mite was enough to last her whole life. At any rate, Marcia’s family continues to mate until the adult bee emerges from the cell with Marcia and her mature daughters in tow. Timmy, as well as any female mites that didn’t have a chance to mature, remain in the cell and die there. No one knows if this is hard on Marcia.
Marcia can repeat this cycle a few more times before she’s all mited out. And if it’s a broodless period, like the dead of winter, Marcia can wait it out while slurping from an adult bee.
As a beekeeper you might be wondering, “Yes of course this tale of Marcia is the most fascinating thing I have ever read, but what use is it, aside from the thrills?” Well, you can use your new-found knowledge about Marcia’s family life against her.
Without brood, mites can’t reproduce. By providing “brood-breaks” in your hives by doing splits, caging queens, or allowing them to swarm (where safe and appropriate!), you can slow the reproduction of varroa. You can also see that more brood equals more mites, and that’s why researchers such as Thomas Seeley recommend keeping bees in smaller hives.
Whatever size hive you have, and whatever the type, I hope the tale of Marcia has given you a little insight into the ways of our unwelcome guest, the varroa mite.
If you'd like to learn even more about the varroa mite's life cycle from a more scientific point of view, check out this research paper