Varroa mite infestation in bumblebees
Varroa mite infestation is a parasitic disease caused by an acarid of the genus Varroa, a small external parasite that normally attacks domestic honeybees (Apis mellifera). In bumblebees (Bombus sp.), the presence of Varroa is much rarer an...
What is it?
Varroa mite infestation is a parasitic disease caused by an acarid of the genus Varroa, a small external parasite that normally attacks domestic honeybees (Apis mellifera).
In bumblebees (Bombus sp.), the presence of Varroa is much rarer and contested. This parasite is highly specific to the domestic honeybee and does not reproduce properly on bumblebees.
Varroa mites may occasionally be found clinging to bumblebees, especially when these insects are foraging near infested hives. This is better described as accidental carriage rather than true varroa mite infestation in bumblebees.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
In bumblebees, the presence of Varroa usually remains inconspicuous.
Occasionally a small, brownish-red, oval-shaped mite may be seen clinging to the thorax or abdomen of the insect.
In cases of significant or prolonged carriage, the insect may appear weakened, with less assured flight or reduced activity.
Malformed or damaged-looking wings have been reported in rare cases, by analogy with what is well documented in domestic honeybees, but this link is not clearly established in bumblebees.
No symptoms are specific: only direct observation of the parasite allows it to be suspected.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The cause is an external parasitic acarid, Varroa destructor or Varroa jacobsoni depending on the region.
This parasite feeds on the internal tissues of the host insect by piercing its cuticle.
In domestic honeybees, its reproductive cycle occurs in the capped brood cells. Since bumblebees do not have capped brood cells in the same way, the complete life cycle of the parasite is generally not possible in them.
The bumblebee therefore acts mainly as an occasional 'carrier' when it comes into contact with infested honeybees or hives, for example by sharing the same flower or water source.
Proximity to honeybee colonies heavily infested with Varroa mites.
Frequent contact between bumblebees and honeybees at shared food sources (flowers, honeydew).
Season of high foraging activity, which increases contact opportunities between insects.
Pre-existing weakness in the bumblebee that may make it more susceptible to parasitic infestation, even if accidental.
Transmission
Direct contact with infested domestic honeybees or with shared surfaces (flowers, hives) is the main mode of parasite transmission to bumblebees. This is not transmission between bumblebees proper, as the parasite does not reproduce in this context.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Diagnosis is based primarily on direct observation of the parasite attached to the bumblebee's body, whether with the naked eye or with a magnifying glass.
A specialist or laboratory experienced in insect pathology can confirm identification of the mite species involved.
For bumblebee colonies used for pollination, systematic visual inspection of insects before introduction into a greenhouse or field is the most accessible monitoring method.
Treatment
No validated and specific acaricide treatment exists for bumblebees, unlike in honeybees.
In practice, manual removal of the observed parasite is sometimes performed by individuals experienced in beekeeping or bumblebee rearing.
Any attempt to treat with acaricide products intended for honeybees is not recommended without specialist advice, due to the risk of toxicity to the bumblebee, whose sensitivity to chemical products may differ from that of the honeybee.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
No specific validated prevention measures exist for bumblebees.
The best indirect protection is to maintain good health management of nearby honeybee colonies to reduce overall parasitic pressure in the environment.
Avoiding the introduction of commercial bumblebee colonies into areas with high Varroa infestation in honeybees can also reduce contact risk.
For bumblebee colonies used for pollination, regular visual monitoring of insects is recommended before placement.
Possible complications
General weakness of the parasitized insect is theoretically possible, with reduced flight capacity or foraging ability.
A role for the bumblebee as an occasional vector of the parasite between different honeybee colonies is sometimes mentioned, but remains debated in the scientific literature.
When to see a veterinarian
Observation of one or more mites attached to a bumblebee's body.
Bumblebees showing abnormal flight or markedly reduced activity within a colony.
Unexplained decline in activity of a bumblebee colony used for pollination.
Before introducing commercial bumblebees into an area with known high parasitic pressure.
Prognosis
The outlook for a bumblebee occasionally carrying one or a few Varroa mites is generally good, as this infestation usually has no major consequences.
Since the parasite cannot reproduce normally in bumblebees, the impact on the health of the bumblebee colony typically remains limited, except under particular circumstances that are still poorly understood.
Frequently asked questions
Can the Varroa mite reproduce on a bumblebee the way it does on a honey bee?
No, generally the Varroa reproduction cycle requires the capped brood of honeybees. In bumblebees, this cycle does not complete normally, so we speak more of accidental carrying than true infestation.
Can a bumblebee carrying Varroa infect a honeybee hive?
This is a hypothesis raised by some researchers, with bumblebees potentially serving as occasional vectors of the parasite between food sources shared with honeybees. However, this role remains debated and has not been clearly demonstrated on a large scale.
What to do if you see a mite on a bumblebee in your garden?
There is generally no cause for concern about an isolated wild bumblebee. If you are managing a bumblebee colony for pollination purposes, it is best to report the observation to a specialist or your supplier.
Is there a self-administered treatment for a parasitized bumblebee?
No, no mite treatment is specifically validated for bumblebees. Using products intended for honeybees without specialist advice is not recommended due to toxicity risks to this insect.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 25 August 2026
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