What Is Varroa destructor?

Varroa destructor is a parasitic mite that attacks honeybee colonies. Since its spread from its original host (the Asian honeybee, Apis cerana) to the Western honeybee (Apis mellifera) in the mid-twentieth century, it has become the single most significant threat to managed honeybee colonies globally. Understanding the biology of this mite is foundational to managing it effectively.

Taxonomy and Origins

Varroa destructor belongs to the class Arachnida, subclass Acari. It is not an insect but a mite, more closely related to ticks and spiders than to the bees it parasitizes. The mite was originally described as Varroa jacobsoni, a parasite of Apis cerana in Southeast Asia. Research in the early 2000s clarified that the mites devastating Western honeybee populations worldwide were a distinct species: Varroa destructor.

The mite's host jump from Apis cerana to Apis mellifera occurred in the twentieth century, most likely in Japan and the Soviet Far East, where beekeepers imported European honeybee colonies alongside the Asian host bee. Apis cerana has developed behavioral defenses against Varroa over thousands of years of co-evolution. Apis mellifera has not, which is why the parasite is so devastating to Western honeybee colonies.

Physical Description

Varroa destructor is visible to the naked eye, though small. Adult females are approximately 1.1 mm long and 1.5 to 1.8 mm wide, reddish-brown, and oval in shape. The mite's body is flattened horizontally, an adaptation for living between the abdominal segments of adult bees and navigating the tight spaces inside capped brood cells.

Males are smaller, spherical, and pale. They never leave the brood cell and die shortly after mating.

Life Cycle

The Varroa life cycle has two phases: the phoretic phase and the reproductive phase.

Phoretic phase: The adult female mite rides on an adult bee, clinging to the cuticle on the abdomen and feeding on bee fat bodies (historically described as hemolymph feeding, but more recent research confirms the primary feeding site is the fat body tissue). During the phoretic phase, the mite does not reproduce. It is waiting for an opportunity to enter a brood cell.

Reproductive phase: The foundress mite enters a brood cell 15 to 20 hours before it is capped, burrowing into the larval food beneath the developing larva. Once the cell is capped, she begins reproducing. She lays her first egg approximately 70 hours after cell capping. The first egg is an unfertilized male. Subsequent eggs are fertilized females. A typical reproductive cycle in a worker cell produces one viable mated daughter mite. In a drone cell, conditions are more favorable: the longer development period allows for more reproductive cycles, producing up to 2 or 3 viable daughters per cycle. This is why mites preferentially infest drone brood at rates 5 to 10 times higher than worker brood.

After the bee emerges from the cell, the foundress mite and her mated daughters exit and return to the phoretic phase on adult bees. The cycle then repeats.

How Varroa Damages Colonies

The direct feeding damage from Varroa is real but not the primary driver of colony collapse. The more devastating mechanism is disease vectoring.

Varroa transmits multiple bee viruses, most critically Deformed Wing Virus (DWV). When Varroa mites feed on larvae and pupae, they inject viruses directly into the developing bee's body. DWV-infected bees emerge with shrunken, crumpled wings and severely shortened lifespans. A bee that would normally live 40 days as a summer forager may survive only days when heavily infected with DWV.

Other viruses transmitted or amplified by Varroa include Sacbrood virus, Acute Bee Paralysis Virus (ABPV), and Israeli Acute Paralysis Virus (IAPV). The fat body damage from mite feeding also compromises immune function, making bees more susceptible to secondary infections.

The result of sustained, untreated Varroa infestation is population collapse. As the mite-to-bee ratio rises, more and more bees emerge as damaged workers. Colony population drops faster than it can be replaced. When mite loads reach critical levels in late summer and fall, the winter bee cohort is irreparably damaged, and the colony dies during winter or fails to build up properly in spring.

Population Dynamics

Varroa populations are slow to build early in the season when brood volumes are expanding rapidly, because the number of mites per bee is diluted by new bees. During summer dearth, when queens reduce or stop laying, the brood volume shrinks but the mite population does not. Mite-per-bee ratios can spike rapidly during dearth. This is why late summer mite counts are the most critical monitoring point of the year.

A colony that shows 1% infestation in June can be at 5% or higher by September if untreated, because mite populations double roughly every month under summer brood conditions.

Why Management Matters

Varroa will not resolve on its own in an Apis mellifera colony. Untreated colonies almost always collapse within one to three years. Management through monitoring, threshold-based treatment decisions, and treatment rotation is the only effective approach with current tools.

The alcohol wash method is the gold standard for measuring infestation rates. Comparing counts against established thresholds, tracking trends over time, and rotating treatment classes to prevent resistance development are the core activities of an effective management program.

VarroaVault is built around this workflow: log mite counts, get threshold alerts, schedule treatments, track your treatment history. Understanding what Varroa mite count methods are most accurate helps you build a monitoring program that gives you reliable data to act on.

Sources

• Anderson DL, Trueman JWH (2000): Varroa jacobsoni is more than one species. Experimental and Applied Acarology 24(3): 165-189
• Ramsey SD, et al. (2019): Varroa destructor feeds primarily on honey bee fat bodies. PNAS 116(5): 1792-1801
• Honey Bee Health Coalition Varroa Management Guidelines
• USDA ARS Bee Research Laboratory
• Genersch E, et al. (2010): The German bee monitoring project: a long term study to understand periodically high winter losses of honey bee colonies. Apidologie 41: 332-352