Phases: dispersal (on adult bees) and reproduction (in capped brood). Entry: about 15–20 h before capping (worker), 40 h (drone). First egg: ~60 h after capping. Mature daughters: 1.8 worker / 3.0 drone. Growth: nearly doubling monthly with brood (Oliver 2017). Threshold: 3 mites/100 bees (Jack et al. 2023).
Varroa mite life cycle
The varroa mite life cycle is tied to the honey bee's own. Varroa destructor is a parasitic mite that feeds on honey bees and can only reproduce inside capped brood cells (Jack et al. 2023). Its life has two phases, as reviewed by Vilarem et al. (2021) and Reams & Rangel (2022):
- The dispersal phase — "previously called phoretic phase" — when an adult female mite rides on adult bees, feeds on them and travels around the hive until she is ready to breed (Vilarem et al. 2021).
- The reproductive phase — inside a brood cell, where she lays her eggs and her offspring feed on the developing bee "from larvae up to imago" (Vilarem et al. 2021).
The calculator above has two modes. Mite cycle in a cell lays out what happens in one worker or drone cell, hour by hour, and how many mature daughters to expect. Mite population estimate gives a rough, clearly labelled projection of how mite numbers in a colony could change over the coming weeks.
Dispersal phase and reproductive phase
Mites spend the dispersal phase on adult bees, mostly nurse bees. When a newly emerged bee leaves an infested cell, the mother and her adult daughters climb on before it exits, and the mites then "switch from riding on the original newly emerged bee to riding on a nurse bee" (Reams & Rangel 2022). Off a bee and out of a cell, a female "can survive a few hours without a host" (Vilarem et al. 2021). In experiments, a single female could complete up to 7 reproductive cycles in her life (Vilarem et al. 2021).
The varroa life cycle and bee viruses
The varroa life cycle matters because of what the mite carries. Deformed wing virus spread by mites "usually kills" an infected bee "within a few weeks" (Otis 2023), and when a colony is heavily infested in autumn, the long-lived winter bees it needs are weakened just as they are being raised (Otis 2023). Models reviewed by Vilarem et al. (2021) suggest that "around 2000 V. destructor females in autumn seems enough to lead to death" of a colony.
Varroa destructor life cycle inside the brood cell
The varroa destructor life cycle inside a cell follows a tight timetable, synchronised with the bee pupa developing next to the mites. Hours are counted from the moment the cell is capped:
- Entering the cell. A female mite slips into a cell containing an older larva shortly before it is capped: worker larvae attract mites for only about 20 hours before capping (15–20 hours, Vilarem et al. 2021), drone larvae for about 40 hours (Reams & Rangel 2022, citing Boot et al. 1992).
- The first egg. About 60 hours after capping she lays her first egg, which is unfertilized and becomes a male (Reams & Rangel 2022).
- Daughters. "The rest of the eggs, which are laid every 24–36 hr, are fertilized and develop into females" (Reams & Rangel 2022). The young mites feed at a wound the mother opens in the pupa.
- Mating. The first daughter becomes adult about 9–10 days after capping, and brothers mate with their sisters inside the cell (Vilarem et al. 2021).
- Emergence. When the bee emerges — 12 days after capping for a worker, 14 for a drone — the mother and her mature daughters leave on it. "The male and all immature females are left behind and die soon after" (Reams & Rangel 2022).
Varroa mite reproduction step by step
Varroa mite reproduction produces more eggs than adults. "A foundress typically produces four to five offspring in a worker cell and five to six offspring in a drone cell", but because the last eggs don't have time to mature before the bee emerges, "the average production of mature daughters in single-infested cells is 1.8 and 3.0 for worker and drone cells, respectively" (Reams & Rangel 2022, citing Donze et al. 1996 and Martin 1998). Those mature daughters are the ones that count: each is a new mother mite.
| Worker cell | Drone cell | |
|---|---|---|
| Mite attracted to the larva before capping | about 15–20 h | about 40 h |
| Cell capped for (bee development) | 12 days (capped day 9, bee emerges day 21) | 14 days (capped day 10, emerges day 24) |
| First egg (male) | about 60 h after capping | about 60 h after capping |
| Later eggs (female) | every 24–36 h | every 24–36 h |
| Offspring laid | 4–5 | 5–6 |
| Mature daughters per mother (single-infested cell) | 1.8 | 3.0 |
Sources: Reams & Rangel 2022; Vilarem et al. 2021; capped periods from the shared honey bee data (Ellis 2015; FAO).
Why varroa prefer drone brood
Varroa invade drone brood far more often than worker brood, for three linked reasons:
- A longer window to get in. "Drone larvae are attractive to mites for around 40 hr before capping, while worker larvae are attractive for only 20 hr" (Reams & Rangel 2022, citing Boot et al. 1992).
- More visits from nurse bees. Drone larvae get "roughly 2.5 times higher visitation rates by nurse bees than worker larvae" (Reams & Rangel 2022), and mites ride in on those nurses.
- More time to breed. A drone stays capped 14 days against 12 for a worker, so more daughters reach adulthood before the bee emerges.
Varroa in drone brood: the numbers
The payoff for the mite is large. With 3.0 mature daughters per mother in a drone cell against 1.8 in a worker cell (Reams & Rangel 2022), a mite in drone brood leaves about two-thirds more offspring. Otis (2023) gives the same picture in round numbers — about 4 young mites mature in a drone cell versus about 2 in a worker cell. The preference isn't fixed, though: it is strongest when drone brood is scarce, and worker-cell invasion climbs once a colony holds about 300 mites (Reams & Rangel 2022, citing Fuchs 1990 and 1992). For how drones themselves develop, see the drone bee page.
How fast varroa populations grow
When brood is present all the time, mite numbers grow exponentially. Writing in the American Bee Journal, beekeeper-scientist Randy Oliver (2017) puts the daily growth rate of varroa in non-resistant European bees during brood rearing at "typically around 0.021" — "nearly doubling each month". At that rate a population doubles in about 33 days, so 100 mites become about 584 in twelve weeks. When brood rearing "is greatly reduced or absent, the mite population will drop" (Oliver 2017), because the mites can't reproduce without capped brood and keep dying of natural causes.
Varroa mite population growth estimate
The population mode turns that into a varroa mite population growth estimate. It is deliberately simple and should be read as a rough guide:
- Lots of brood: growth at the 0.021-per-day rate (Oliver 2017).
- Some brood: no published rate fits this case, so the tool shows a range — from no growth up to the full-brood figure.
- Little or no brood: no increase; the mites can't breed, and numbers fall (Oliver 2017; Jack et al. 2023). No sourced rate of decline is given.
Real colonies don't follow a formula. Mites also arrive on drifting and robbing bees — Frey and Rosenkranz estimated 30–60 mites invading colonies per week in autumn, cited by DeGrandi-Hoffman et al. (2016, Experimental and Applied Acarology) — and climate matters: in a University of Florida study, mite levels rebounded "rapidly after treatment in the summer and fall seasons when honey bee brood is plentiful", but stayed below the economic threshold for 4–5 months after winter or spring control (Jack et al. 2023).
Why mites seem to explode in late summer
Mite numbers look as if they suddenly jump in August and September, but much of that is timing: while brood is abundant many mites are hidden in capped cells, and when the bee population shrinks after the main flow, the same mites are spread over fewer bees (Oliver 2017). Otis (2023) describes mite-susceptible colonies in which the mites are barely noticeable in spring, conspicuous by August and seem to have exploded by September.
Monitoring varroa (the basics)
The only way to know where a colony stands is to count. This section covers the general idea only; for when and how to act on a count, follow your local apiculture service, Extension apiarist or beekeeping association.
How to check for varroa mites
- Alcohol wash: a sample of 200–300 bees is taken from the brood area, the mites are washed off and counted, and the result is expressed as mites per 100 bees (Jack et al. 2023, following Dietemann et al. 2013). It is the more accurate method, but the sample of bees dies (Bava et al. 2022).
- Powdered-sugar roll: the bees are rolled gently in powdered sugar, which makes it hard for mites to hold on, and the mites are shaken out and counted; the bees are returned alive (Bava et al. 2022). In that study it was more accurate than a CO2 method in the same device.
Varroa threshold
The economic varroa threshold "is typically considered as 3 mites/100 adult bees" (Jack et al. 2023, citing Jack & Ellis 2021), and "the more time a colony spends above the economic threshold, the more likely it is to experience both increased viral infection and colony mortality" (Jack et al. 2023). Thresholds differ by season and region, so check the figures your local apiculture service uses. This site doesn't give treatment advice: products, timing and doses must follow the label and local guidance.
How this calculator works
- Cell mode: capping and emergence days come from the shared honey bee data used on every bee page (worker capped day 9, emerges day 21; drone capped day 10, emerges day 24; Ellis 2015; FAO). Mite timings and offspring numbers come from Reams & Rangel (2022) and Vilarem et al. (2021). The timeline marks entry, capping, the first egg at about 60 hours, the first adult daughter at 9–10 days and emergence.
- Population mode: N(weeks) = start × e0.021 × days for lots of brood (Oliver 2017); a range from the starting number up to that figure for some brood; no growth for little or no brood. Results are flagged when they pass about 300 mites (when worker-cell invasion rises; Reams & Rangel 2022) and about 2,000 mites (the autumn level models link to colony death; Vilarem et al. 2021).
- What it can't do: it doesn't know your colony's size, the mites arriving from other hives or the effect of any control you use, so it can't tell you a mites-per-100-bees figure. Only a wash or sugar roll can.
Frequently asked questions
What is the varroa mite life cycle?
Two phases: a dispersal phase riding and feeding on adult bees, and a reproductive phase inside capped brood cells, where the mother mite lays a son and several daughters (Vilarem et al. 2021; Reams & Rangel 2022).
How long is the varroa life cycle in a cell?
As long as the bee stays capped: 12 days in a worker cell and 14 in a drone cell, plus a short time before capping when the mite gets in.
When does a varroa mite enter a brood cell?
Shortly before capping — about 15–20 hours before for worker larvae and about 40 hours for drone larvae (Vilarem et al. 2021; Reams & Rangel 2022).
How many offspring does a varroa mite have?
She lays 4–5 eggs in a worker cell and 5–6 in a drone cell, but on average only 1.8 and 3.0 daughters mature (Reams & Rangel 2022).
Why do varroa mites prefer drone brood?
Drone larvae attract mites for longer before capping, get more nurse-bee visits and stay capped longer, so more daughters mature (Reams & Rangel 2022).
How fast do varroa populations grow?
With plenty of brood, about 0.021 per day — nearly doubling each month (Oliver 2017). With little or no brood, numbers fall.
Can varroa mites reproduce without brood?
No. They only reproduce inside capped brood cells (Jack et al. 2023).
How long can a varroa mite live off a bee?
Only a few hours when it is off a bee and out of a brood cell (Vilarem et al. 2021).
How do beekeepers check for varroa mites?
With an alcohol wash or a powdered-sugar roll of a few hundred bees from the brood area, counted as mites per 100 bees (Jack et al. 2023; Bava et al. 2022).
What is the varroa threshold?
Typically 3 mites per 100 adult bees as the economic threshold (Jack et al. 2023). Local guidance may differ by season.
How many mites can kill a colony?
Models suggest about 2,000 mites in autumn is enough to lead to colony death (Vilarem et al. 2021).
For education. Bees are pollinators — never spray a swarm or a colony. For a swarm or bees in a wall, contact a local beekeeper, a certified bee-removal specialist or your Extension office (UGA Extension; Mississippi State). Follow your local apiculture or Extension guidance on varroa and colony care. If a sting causes trouble breathing, swelling of the face or throat or faintness, call emergency services.