Understanding Mite Counts

As we’ve discussed in our recent PerfectBee Snippets, (see the Learn More section below for all our Varroa Snippet links) managing Varroa mites is one of the most important tasks a beekeeper should be completing to keep their honeybee colonies as healthy as possible.  

Because Varroa mites pose such a large threat to even a robust colony and can multiply rapidly, staying on top of monthly mite testing can help ensure things don’t get out of control.

It’s not only the testing itself that’s important, however. Being able to interpret your mite count results and understand what that means for the mite levels in your hive can make all the difference in making better beekeeping choices.  

Mites Per 100 Bees

When you use the alcohol wash or sugar roll method to test for varroa mites in your hive, the sample size and mite count thresholds are roughly the same. A sample is roughly 300 nurse bees (about ½ cup of bees, lightly “packed”) from brood frames that have open larvae.  

Keep in mind that the alcohol wash method is the most accurate as bees die and mites are easily dislodged from their bodies in the process, giving you a better idea of how many mites are truly present. The sugar roll method is less accurate but still preferred by those whose colonies are too small or weak to sacrifice the 300 bees that will die in an alcohol wash.  

When you complete a test with a 300 bee sample, you’ll divide that count by 3 to find the mites per 100 bees. For example, if you find 27 mites after an alcohol wash, you’d divide 27 by 3 to get 9. That means for every 100 bees in the hive, there are at least 9 mites. 

Treatment thresholds are based on percentages, which is why it helps to get the number of mites per 100 bees first. 9 mites per 100 bees comes out to be about 9%.  

Here’s a reminder of the treatment threshold guidelines most beekeepers use:

  • During the months of April to July, the recommended treatment threshold is 2% or 2 mites per 100 bees.    
  • In most areas, during the months of August to October, the thresholds are a bit higher at 3% (3 mites per 100 bees). The higher threshold is because as brood production decreases in the fall, the number of mites in cells decreases but the number of phoretic mites (mites on bees) will increase. Varroa populations also spike in the fall, leading to an expected increase in numbers.    

Adjust these threshold timings to your location in case you don’t have the typical northern brood breaks during the colder months. Read on to learn more about seasonal and local considerations. 

No matter the time of year, if you find more than 3 mites per 100 bees during your mite tests, treatment should be considered as soon as possible, before the mite levels get to an even further damaging point.   

Assessing Mite Drop Counts on Sticky Boards 

Some bottom boards have a “Varroa screen monitoring tray” that allows you to get a rough idea of the number of phoretic mites inside your hive. Though this isn’t the most accurate method as it only counts the mites that have naturally fallen off of or have been groomed from bees in the hive (whereas a sugar roll or alcohol wash dislodges mites from bees, leading to more accuracy), it is a less invasive way to get a rough idea of mites present at any time of the year. It offers little disturbance to the bees and can easily be completed either in a 24-hour period or over 3 days.  

Keep in mind that a lot of debris falls to the bottom of a hive within that time, though, which can all look pretty similar to a varroa mite. It can be difficult to find the mites among the fallen debris, but you’ll want to find as many mites as you can and count them all. If you’re completing a 24-hour mite count, that’s your rough mite estimate per 100 bees. If you’ve taken a count over 3 days, divide the number that you find by 3 to get the 24-hour mite count.  

If counts from a sticky board test, per 100 bees, exceed 8 per 24 hour period between the months of April to July, or 12 from August to October, it’s a definite sign to complete a more accurate method for mite level testing (like the alcohol wash).  

Sticky boards aren’t always the most accurate method, but they are a great, low-impact option for beekeepers to keep an eye on mite levels in their hive and take further action when a problem is suspected.  

Seasonal and Local Considerations 

As we mentioned in previous Snippets, Varroa mite populations tend to spike whenever bee populations do. This means that paying close attention to not just how many mites are present, but also what else is going on in and around the hive can help any beekeeper to better be prepared to fight mites.  

Especially during the summer months in most places, it’s important to keep in mind that bees can very quickly bring a high mite load to the colony (even after being treated) if they robbed a diseased or weak colony. And the same goes for robbers visiting your hives, they could bring in high levels of mites.  

Some local beekeeping clubs or state agencies may have guidelines for beekeepers in that area to use when testing and treating for mites, based on the number of honeybee colonies and possible mites they estimate to be in that locality. Check with your local beekeeping club or state’s website for more details on the local recommendations for your area.  

When Treatment is Required 

If you’ve determined that mite levels in your hive are above the recommended treatment threshold, mite treatment should be applied quickly, but remember to give the bees some time (2-3 days) to recover from the inspection and testing you just completed.  

Keep in mind that applying treatment after thresholds are met or exceeded is a reactive way to approach mite infestations. Knowing the patterns of bee population and mite population growth throughout the season using Integrated Pest Management techniques allows for a more proactive way to plan for tackling mites before and during times you know that the population may spike.  

Using an IPM plan to ensure you have mite treatment on hand before you find high levels of mites in your hive can make it much easier to apply a treatment quickly and can help consistently keep mites at a more manageable level.

Keep an eye out for an upcoming PerfectBee Snippet where we’ll go over the details of some commonly used varroa mite treatments and how to choose the right one for you and your bees.  

Learn More

We’ve compiled some of our free resources below, with articles, guides, lessons, and blog posts specific to the dreaded Varroa Destructor Mite.

As is the case with most beekeeping tasks, there are special tools and pieces of equipment that can help with managing Varroa mites in your bee yard. Check out the PerfectBee Store to find all of your Varroa mite testing, management, and treatment needs. Here are a few of our favorite options: 

  • Varroa EasyCheck – For measuring a mite count using the alcohol wash method. 
  • Sugar Roll Testing Kit – For assessing mite count using the sugar roll method. 
  • Oxalic Acid Kit – A kit that gives you all you need to complete an oxalic acid dribble 
  • Drone Frame – Adding a drone frame to your hive can help manage varroa mite levels, but only if timed perfectly right before the drones inside emerge and a ton of mites emerge with them! 
  • The Langstroth Screened Bottom Board and Varroa Monitoring Tray – Use the screened bottom board with tray to take a 24-mite count by counting how many phoretic mites fall off of bees within that time period 
  • A Field Guide to Honeybee Maladies – An excellent guide to many honeybee viruses, diseases, and pests. Includes information and photos of Varroa Mites and the issues they cause. 

Colony Member Resources

Colony members, check out these member-only Academy lessons to learn even more about Varroa Mites: 

And head over to the Colony Forum to view some interesting discussions specific to Varroa Mites: