How to Test for Varroa Mites
One of the major struggles facing beekeepers today is the presence of parasitic Varroa mites in their colonies. This common pest of honey bees is the #1 killer of colonies worldwide. How do you know if your bees are infested and how big of a problem you have? The beekeeper needs to learn how to test for varroa mites in their colonies.
Testing for Varroa Mites in Your Hives
Many (or most) honey bee colonies have some varroa mites in residence. It is the level of infestation that beekeepers must monitor to keep healthy bees.
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And no, you can not rely on visual inspections by the time you see mites on bees – it may be too late to do anything.
Unfortunately, testing for varroa mites is not a one and done procedure. If you live in a region with mites (and most folks do), monitoring mite levels is a season long activity.
What do Varroa Mites Look Like?
Varroa Mites (Varroa Destructor) are an external parasite of adult bees and bee brood. They are flat, reddish brown and oval shaped and about the size of a pin head.
They can be be seen with the naked eye. But, they often burrow in between the exoskeletal plates of adult bees. It takes a sharp eye to see them.
Varroa Mites are native to Asia where they parasitize colonies of Apis Cerana (the Asian Honey Bee). Apis Cerana shows some resistance to these mites that they have lived with for many years – our bees (Apis mellifera – European Honey Bee) have no resistance.
As mites feed on adult honey bees, this weakens the colony. Worker bees are sickly and less productive. Infected bees do not live as long and this results in an overall unhealthy colony.
Varroa are also vectors for many viruses and diseases. They can carry and spread these pathogens to other members of the hive.
Why Visual Testing Doesn’t Work
Because these are external pests that can be seen with the naked eye, you might think you can just look, right? Can you check your bees for mites by looking? Well, yes you can but its not easy or reliable.
There is no way you can get a true visual assessment of varroa mite numbers. This is because at any given time the vast majority of mites are inside capped brood cells.
By the time you see adult mites on the bees, it could be too late for the colony to rebound from the infestation.
Once enough bees are sick and enough disease is spread, the colony reaches a point of no return. This is why we use various methods of checking mite levels regularly.
Monitor for Exploding Mite Populations
The life cycle of Varroa Mites and the honey bee life cycle weighs heavily in favor of the mites. They can identify whether a larva is worker or drone brood. They will use both but drone brood is preferred.
A mated adult female Varroa enters a cell and begins to feed on the larva that is near the capped stage. Sixty hours later, she gives birth to a male mite.
After 30 more hours, a female mite is produced. The adult mite pierces the young bee so she and her daughter can feed. The male mite does not feed. He mates with his sister(s) and dies.
When the adult bee emerges, the mother and daughter mite leave the cell and attach to another adult bee. The female mite has time to produce 1 mature daughter (maybe 2) in a worker brood cell.
However, if she inhabits a drone cell (with a longer time capped in the cell) she can produce 2 to 3 daughters.
Basic Schedule for Mite Counts
Determining when to treat your bees for mites involves many factors beyond just a date on the calendar. But, we know the bare minimum schedule.
- very early Spring
- early Summer (Late May-June)
- Late Summer (August)
- Late Fall (October)
While the ideal situation would be to have colonies with zero mites, that is not usually possible. Most colonies do have some mites and they do deal with the situation well.
However, it is important to keep the level of mite infestation low. After the number of mites rises to a certain level, colony health is affected.
This is especially true in late Summer. This is a time when most colonies begin to reduce the size of the brood nest. The mites however, do not slow production and this results in most of the bee brood becoming infected.
If you fail to do regular mite checks for varroa, your colony may already be dead (even though the bees are still there) even before you notice a problem.
Varroa Mite Count Testing Methods
The level of mite infestation can be determined by several methods. Each method has benefits, as well as, drawbacks and limitations.
- alcohol wash – soapy water
- sugar shake
- sticky board drop
Testing for mites is certainly necessary because you need to know: 1) if you need to treat your hives for mites, and 2) if you treated – did it work? Don’t skip this step of checking your colony for varroa levels – even after you have treated.
Alcohol Wash Method ( or Soapy Water)
Take 300 bees from the brood frame area of the hive. Just shake the nurse bees off the frame into a box or collection container (don’t get the queen !!!). This is about ½ cup of bees.
Pour bees into a wide mouth glass jar with a small mesh wire for a lid. You can make your own jar or purchase one ready to use. Add soapy water (or 70% isopropyl alcohol) and shake gently for a minute.
Pour liquid through the mesh wire to strain out the bees. Then re-pour liquid through a smaller mesh filer (coffee filter, cotton cloth etc).
Count the mites. (A similar method uses Ether in the same manner). Of course this kills the bees you are using!!!
*It is better to sacrifice 300 bees than to allow thousands to die due to varroa infestation. (But, I just cannot do this. ☹ Beekeeper Charlotte)
Powdered Sugar Shake Method
Harvest 300 bees as above but don’t get the queen! Pour bees into wide mouth glass jar fitted with a mesh lid. (#8 mesh hardware cloth).
Or you can purchase a testing unit from Mann Lake (that’s what I use). Simply brush the bees off the frame into the cup basket until you get the needed amount. Then, add 1 – 3 Tablespoons of powdered sugar to the container, put on lid and gently shake.
If you need to, set the jar in the sun for a minute (very briefly) to increase humidity. Gently shake the sugar out of the jar (thru the mesh lid) onto a white surface and count the mites.
Release the sugar-coated bees. (Warning – they will be alive but they may not be happy!)
Determine the Level of Varroa Mite Infestation
How many varroa mites is too many? To determine infestation percentage: Divide the number of mites by the number of bees.
If you find 12 mites: 12 divided by 300 = 4% infestation. Most resources consider numbers over 3% to be a high mite level. I am unhappy with anything over 2%.
If your infestation level is below 2%, you may decide to test again in a month or go ahead and treat – it is your call.
Natural Drop Using Sticky Boards
Every day mites and bees share the space inside the hive. In the normal hustle and bustle, some mites will fall. Researchers have determined a guideline for detecting the level of infestation.
Screened bottom boards normally come with a white grid board that can be inserted for performing mite checks. Don’t leave that board in all the time – it cuts down on important hive ventilation.
Apply a thin coating of Vaseline or cooking spray to one side of the white board. You can also buy liners that are already sticky if you wish.
The greased sticky board is placed under the screen bottom for 24 hours and then removed. The screen prevents bees from getting stuck on the board.
If you have solid wood bottom boards, you can purchase a special screen insert to allow counting. Inspect your sticky board and look for mites. How many do you see?
Most experts recommend that more than 50 mites dropped in a 24-hour period is too many. However, this is a highly contested number because there are so many variables.
Sometimes, mite infestations do not kill a colony until the second year. It takes that long for a strong colony to become so weak and diseased that it will fail.
Mite Checks are Essential
As you analyze your mite counts, you have to consider when it is time to treat your colonies for varroa. The mite counts are the beginning but there are other things to consider as well.
In the world of beekeeping, we find 2 situations involving varroa mites and bees. The colonies that have mites and the colonies that have mites but the beekeeper doesn’t think they do.
If growing varroa levels let you know it is time to do something, it is time to consider your options. There are many varroa mite treatments to try – find one that works for you. Do not let anyone convince you that your new colonies have no mite worries.
I have had healthy packages build up, make honey for themselves and me, be strong in July and dead by late November.
You cannot assume everything is okay. Be a good beekeeper and monitor your honey bee colonies by performing routine mite checks.
Honey bees have a marvelous system for Winter survival. But, many colonies die during winter as the weak bees cannot sustain the hive. Many of these problems result because beekeepers fail to test for varroa in mid-late Summer.