The signs of mite damage- How to identify progressed varroosis

Varroa infested colonies entered the United States in ~1987, and changed beekeeping forever. Beekeeping has always been time consuming, difficult and experience oriented; however, beekeeping changed when beekeepers had to apply an insecticide to an insect. Since introduction, beekeepers have reported high annual colony losses due to mites. In fact, some beekeepers report 60% losses due to this troublesome pest. While beekeepers have faced devastating challenges before, including American Foul brood, varroa mites has presented damage never seen before.

Varroa mites have become more difficult to manage since its introduction in 1987. Varroa mites are seemingly embedded within the honey bee industry as nearly, if not all, colonies have varroa. Like many beekeepers say ” all my colonies have mites, I just cannot see them”. Even if alcohol washes do not reveal mites, varroa is present in the brood or will be present soon due to infestation from surrounding colonies. As mites have become more widespread, they began to transmit virulent strains of viruses. In fact, Researchers are finding more and more variants of Deformed Wing Virus, a virus that infects honey bees. Research has shown that DWV-B (Deformed Wing Virus variant B) can be responsible for high over-winter losses. My point is varroa devastates colonies because of viruses, and it seems varroa are transmitting more virulent strains of viruses than 10 years ago. Because of this, I want beekeepers (what I recommend to commercial beekeepers) to keep mite levels below 1 mite/ 100 bees in the spring and 3 mites/100 bees in the fall. If higher, they risk high colony losses. Even 5 years ago, colonies could withstand 5-6 mites/ 100 bees in the fall and be fine. However, as mites transmit more virulence viruses, the more control needed.

Monitor, Monitor, Monitor

Beekeepers must consistently monitor mites if they expect to have strong and healthy colonies. Beekeepers can monitor their mites two ways: either perform a alcohol wash (or other method) or observe the overt signs of mite damage. It is ideal to perform monitoring methods once a month, but this is not always possible. Because of this, both monitoring methods are a great idea. But mites should be monitored at least 4 times a year as seen in figure 1: population increase, population peak, population decrease, and fall dormant. I will detail these phases in this post, but it is essential to understand the seasonal changes. For example, brood quantity differs throughout the year, so certain treatments are less effective. By understanding seasonal cycles, beekeepers can better manage their mites. I understand figure 1 does not “fit” with every region so please bear with me.  Some regions have multiple population peaks due to  large honey flows, so you will need to understand the Honey bee seasonal phases in your region. But essentially, as the bee and brood population increase, so does the mites.

Screen Shot 2018-05-07 at 9.08.00 PM.png
Figure 1: Honey bee seasonal phases from the honey bee health coalition- Beekeepers should monitor mites once a month, but this is often not possible. But mites should be monitored at least 4 times a year: late winter-early spring dormant, population increase, population peak, population decrease, and fall dormant. I recommend alcohol washes (or another method) during these periods. Photo courtesy of the Honey Bee Health Coalition

Mite Monitoring Techniques

I will detail monitoring techniques in different post, but I attached a chart outlining the 3 major mite monitoring techniques I recommend. Like I mentioned earlier, one of these techniques SHOULD be used 4 times a year: Early spring, late spring, late summer and early fall. Each beekeeper has their preference, so use the method you feel the most comfortable with. I use alcohol washes, but I feel comfortable with sugar rolls or CO2. As long as you monitor, there is not a wrong method!

Advantages  Disadvantages 
Sugar Rolls
  • Known research on accuracy
  • Common method
  • Does not kill bees
  • Messy
  • Hard to do on windy, rainy or humid days
  • More time consuming
Alcohol Wash
  • Known and common method
  • Quicker than sugar rolls
  • Can be more accurate than sugar roll
  • Can be messy
  • Kills bees
  • Quickest method
  • Easy to do with multiple colonies
  • Kills the bees (most likely)

When monitoring mites, beekeepers should aim for mite thresholds. I outline my recommended thresholds for each monitoring method below. If your colony is above threshold, I recommend taking action. I will detail mite control methods in a post later this week. Mite thresholds is not a perfect science, but if levels are higher, you may place your colonies at an avoidable risk. Even if you have levels below the threshold does not necessarily mean your colonies will be healthy and successful. For example, I have sampled many commercial beekeepers with mite levels <0.5 mites /100 bees in the spring, and they eventually had huge losses. I typically see mite levels spike in the late summer because: A) a summer treatment with honey supers are limited, B) Mites are often lurking in the brood, and C) Mites from other beekeepers can infest your colonies. Because of this, always monitor and never be content. Once mite levels do spike, they may be difficult to bring down. By the time you notice, the mite damage is already done.I should note that I recommend alcohol washes, powdered sugar rolls or CO2 over a sticky board. Sticky boards just are not nearly as accurate. If a sticky board is your only option, sure. But try using the other options for more accurate results.

Monitoring Method # of mites in early-spring # of mites in mid-spring # of mites in late-spring # of mites in early-fall # of mites in late-fall
Alcohol Wash  

1 mite/100 bees

1 mite/100 bees 1 mite/100 bees 3 mite/100 bees 3 mite/100 bees
Powdered sugar roll 1 mite/100 bees 1 mite/100 bees 1 mite/100 bees 3 mite/100 bees 3 mite/100 bees
CO2 1 mite/100 bees 1 mite/100 bees 1 mite/100 bees 3 mite/100 bees 3 mite/100 bees
Sticky Board 9 mites/24 hours 9 mites/24 hours 9 mites/24 hours 12 mites/24 hours 12 mites/24 hours

Disease Progression 

I inspect and observe hundreds of colonies annually. When I enter a colony, I often immediately know whether the colony has (or did) have mite levels simply by observing progressed signs of mite damage. Just observing progressed mite damage does not suffice, but it is a great start. By observing these visual signs, you will know just how bad your mite levels are and the possible action needed. Like I said earlier, monitoring mites should be done once a month, but this can be time-consuming and unlikely for many beekeepers. At least, if you observe these visual signs, you will understand the extend of mite damage.

I outlined the 5 stages of mite damage, which I relay to my beekeepers. In the spring during population increase, I want to see colonies within the Stage 1- 2. While I hate to see mites in the spring, this is not always a bad sign. Even if I observe mites, the colony may be below the recommended threshold, so just monitor that colony. During the late spring, summer and fall, I like to see colonies within Stage 1-3. Even if Chewed Down brood (which I outline below) and phoretic mites are seen, this does not mean beekeepers have high levels. However, a combination of phoretic mites and chewed down brood can signal worse mite issues. If these signs are seen, continue to monitor these colonies. As for Stage 4-5, I never want to see these stages, regardless of temporal period. Deformed Wing Virus and Parasitic Mite Syndrome can signify high mite levels.  Specifically for Parasitic Mite Syndrome, this disease signifies very progressed mite damage, which often results in colony deterioration and eventual colony death. If colonies are in stage 4 or stage 5, monitor immediately to determine extent of damage. Action is often required, but may be too late.

 Stage Visual Signs Notes
Stage 1 Zero signs of mites, brood diseases or viruses
Stage 2 Visual signs of phoretic mites on either workers or drones.


This does not necessarily mean a mite issue exists, but if mites are seen, monitor to determine extent of varroosis.


Stage 3 Chewed Down Brood and/or phoretic mites


Stage 4 Deformed Wing Virus (DWV) and/or Chewed Down Brood and/or signs of phoretic mites. Visual signs of Deformed Wing Virus (DWV) can mean larger varroa issues. Obviously, this depends upon the number of bees with DWV and the number of phoretic mites seen, but mite monitoring is recommended to determined extent of varroosis. These signs signal a more progressed form of varroosis.
Stage 5 Parasitic Mite Syndrome (PMS) and/or Deformed Wing Virus (DWV) and/or Chewed Down Brood and/or Phoretic mites Visual signs of Parasitic Mite Syndrome usually signal extreme issues with varroosis. If Parasistic Mite Syndrome is seen, then mite levels are often a significant issue and has advanced to the most progressed stage of varroosis.

Visual signs

Phoretic Mite

Phoretic mites are Varroa mites seen on the abdomen of worker (or drone bees). Most phoretic mites, however, are found underneath the bee. Because of this, I typically inspect the ventral abdomen of several worker bees during inspections. This is why beekeepers “never see mites”, even if these beekeepers have  higher mite levels. Visually inspect phoretic mites just on the workers, not the drones. If phoretic mites are seen on worker bees, than this represents a more progressed infestation of mites. Signs of phoretic mites indicate the colony is in Stage 2-5. Visually inspect other signs to further pinpoint extent of damage.


Screen Shot 2018-05-12 at 10.38.32 AM.png
Phoretic mite on the thorax of a worker bee. Photo Courtesy of Rob Snyder

Chewed Down Brood

Bees can sense mites in the brood. If sensed, bees will uncapped and cannibalize the pupae. If chewed down brood is seen, then mites may be at a high level, especially within the brood. Chewed down brood can indicated progress mite damage, so continue to monitor and assess colony health is seen.

Screen Shot 2018-05-08 at 7.37.06 AM.png
The bottom right corner contains a cell with chewed brood. Bees begin chewing brood when they sense mites within the cell, so this can indicate larger mite issues. Photo by Rob Snyder

Deformed Wing Virus (DWV)

Deformed Wing Virus represents the next stage of varroosis progression. Bees with Deformed Wing Virus are kicked out of the colony so if bees with DWV are seen than Varroa has become an issue. Deformed Wing Virus does not signify un-manageable mite levels for the colony, but it is a more progressed sign of mite damage.

This bee has deformed wing virus, a debilitating virus than can easily deplete a colony. Oftentimes, bees with the virus are removed from the colony. So if bees with Deformed Wing Virus are seen, than this can indicate larger issues. Photo by Rob Snyder

Parasitic Mite Syndrome (PMS)

A pathogen has not been identified for this diseased, however mites are always present when this disease is seen. This brood symptom looks similar to other brood diseases except the larvae do not rope like foulbrood. Larvae do appear sunken to the side of the cell. If Parasitic Mite Syndrome is observed, than colony has likely dwindled and deteriorated. Parasitic Mite Syndrome is the most progressed sign of mite damage, and truly at a stage of no return. Even if low phoretic mites are seen, parasitic mite syndrome often means an end to your colony, even if treatment is applied.

  • Spotty brood and varroa present on adult
  • Mites may be present on brood
  • Mites seen on open brood cells
  • Small population size
  • No odor present, just sunken brood
Screen Shot 2018-05-08 at 7.36.32 AM.png
Parasitic mite syndrome is the most progressed sign of mite damage. If parasitic mite syndrome is seen, than the damage is done. These colonies will likely collapse, and there is nothing a beekeeper can really do. At this stage, the colony has already dwindled and deteriorated.


All beekeepers should consistently monitor mites throughout the year. Even if mite levels are low at one point, does not mean they will stay low. Mite levels can easily spike, so always be aware. Beekeepers should learn how to monitor mites and visually inspect mites. By doing so, varroa mites can effectively be managed. Varroa mites are the most challenging issue beekeepers face, so make sure you know where your colonies stand. If you don’t, then you risk losing your colonies.

If you enjoyed this blog, please subscribe to my blog. Subscription helps bring people to my blog, which I hope informs folks. Follow us on Instagram and twitter. Please join my facebook group, it is a close group but a great place to see my posts! I post really cool pictures along with my blog posts, so follow these pages for daily alerts!

Garett Slater


One comment

  1. Very good explanation of the different stages to look for. Thanks for all your posts. I have learned something from each.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s