varroa mites

Faster than the speed of mite

Let’s say you have a brand new colony of bees that is guaranteed to be uninfected by Varroa mites. How does your colony become infected and how fast do the mites reproduce? Let’s take it from the top:

  1. One fine spring day one of your bees shares a flower with an infected bee from another colony. Busy doing what bees do, they rub against each other as they seek nectar or pollen and, bingo, a phoretic mite (a mite taking a ride) passes from the foreign bee to your bee.
  2. Your bee flies home with her load of goods: two full pollen sacks and a gravid (pregnant) female Varroa mite. You are toast.
  3. Once in the hive, the mite jumps off her ride and cases the joint. She breathes in luscious smells—larvae in their fifth day of development, just ready to be capped. She especially likes the smell of those drone babes, but there are so many cranky bees around, she decides to crawl into a worker cell before the bees have a chance to cart her away.
  4. She scuttles down to the bottom of the cell and submerges herself in brood food with only her breathing tube breaking the surface. She hunkers down and waits, a mite at the end of the tunnel. Patience, she knows, is a virtue.
  5. Eventually the immature bee consumes the brood food and the female mite crawls free.
  6. Meanwhile, the honey bee larva has transformed into a pupa and the mite pierces her soft young body and feeds, vampire-like, on the bee’s hemolymph (blood). Yum. Slurp, slurp.
  7. The mite feeds for about 60 hours, building her strength for the business of egg-laying. The first egg she lays is haploid, meaning it has only half of a full complement of chromosomes. This grows into a small but mighty male mite.
  8. Then, once every 30 hours, she lays another egg. All of these subsequent eggs are diploid, meaning they have a full set of chromosomes and are female.
  9. All the mites go through a series of stages: larva, protonymph, deutonymph, adult. As adults, they mate while still within the capped cell. After the male mite mates with his sisters, he dies. Good riddance, but the damage is already done.
  10. The female mites continue to live off the female worker bee until she emerges from her cell. These mites are then carried about the hive where they smell those piquant five-day-old larvae. When they get to feeling frisky, they jump off their steed, crawl under a larva, and prepare to start a family of their own.
  11. But now, instead of one gravid female mite, you have 2.2 gravid females. (Okay, from a practical point of view, it’s just two. But the 0.2 becomes statistically significant as the population builds. Simply put, every fifth cell yields 3 gravid mites.)

The time spent in the larval stage varies bee-by-bee, which is why some cells produce more mites than others. And the drone larval stage is naturally longer, so each drone cell can produce more mites than a worker cell. Nevertheless, the actual number of reproductive mites produced per cell is smaller than the theoretical number because not all eggs are viable and not all mites are able to reproduce. Thank heavens there is something on our side.

Still, the increase in mite populations is staggering, and it doesn’t take long for a colony to become overwhelmed. And anything that increases the time honey bees spend in the larval stage—such as some pesticides—can dramatically and quickly increase the Varroa mite load.


Adult varroa mite on honey bee larva. Wikimedia Commons photo.

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  • I have a question for you about powder sugar dusting for mites, inspired by Emily’s Adventuresinbeesland post of oxalic acid in winter.

    This fall both my hives had some mites, 50-60 collected on the sticky board after 24 hours. This level was pretty consistent for the ~6 powder sugar dustings that I did in the fall. I stopped when it started to get cold and wet (still had same amount of mites). I use 2 methods: shaking/brushing through a screen on top of each box, and with the “dustructor” that brushy mountain sells (which lets you blow the p.s. up through the hive so you don’t have to open it up).

    Emily was saying they are treating in winter because the adult mites are hanging out on the adults because of the lack of brood. We are having some unseasonally dry, sunny weather. What do you think about using the dustructor this winter, on a sunny, dry day (or a few times if we get that, weather-wise) in which a lot of bees are flying? Or should I just leave them be until later? I just had never heard of treating in winter around here (I am also in W. WA).

    Thanks so much!

    • Hi Gretchen,

      Interesting question. It is true that adult mites are riding around on adult bees this time of year because there is so little brood. It is also true that phoretic mites (those riding around on adult bees) are the ones you dislodge with powdered sugar. Put together, it seems like winter would be an ideal time to use powdered sugar.

      However, these are the issues I see. If it is cold enough that the bees are clustered, not much sugar would make its way into the cluster. So, if you do as you suggest, and dust them on one of the dry, warm days, it might just work. I don’t see any harm in it and it may do a decent job.

      The other issue is you would have to leave your varroa drawer out, if you have one, so that the mites drop through and don’t return to the hive. But if it’s warm enough for dusting, it’s surely warm enough to leave out the varroa drawer.

      I think you should monitor the moisture in your hive as well. If it’s too wet in there, the sugar may clump on the bees instead of coating them lightly. So good ventilation would also be an issue.

      I say you should try it, but check for moisture first, and then take a look and see how it coats the bees before you decide to do it again. Remove your varroa drawer after you do your counts so the mites fall out. (Or perhaps you use oil or a sticky drawer, which are also fine.)

      If you try it, please report back. I’d like to know how it works.

  • Hi Rusty,
    Well, the weather presented me with the opportunity to try yesterday. It was about 55 degrees and sunny. Last week I peeked in to check ventilation and stores, and the hives were well stocked and dry under the inner cover. They were dry yesterday as well, so I used the dustructor, and the PS blew up through the hives normally (could see it coming out the cover, which was propped open, at the usual amount of PS it takes for me to see that), so I presumed it covered them adequately. Today the sticky board showed some mites (26 & 16), and I pulled the board so they are back to their normal ventilation flow. I will call it a success. 26 & 16 seem like pretty low levels (certainly lower than in the fall), but I will dust again this winter if the weather gives me the opportunity. I’d like them to enter spring with as few mites as possible.

    Thanks for the input — and thanks for the great blog!

  • Once a nuc is installed in a hive, how long should one wait before performing an alcohol wash to check for mites and treating if necessary.


  • Rusty,

    The reason I ask is that the alcohol wash will kill the bees used for the mite count. Would sacrificing a half cup of bees have a negative effect on the population of the hive if done too soon after the nuc is installed? Would a better choice be to wait until comb has been drawn out on the hive frames? Thanks.


    • Carl,

      Yes, I know why you asked. The problem as I see it is that a nuc in spring is about to undergo massive brood rearing and growth. If you have mites now, their population will explode as well, right along with the brood. If you could avoid that exponential growth, you could avoid a lot of heartache later. The sacrifice of a half-cup of bees seems like a small price to pay.