Below is a photograph of a Bombus pratorum worker, foraging on a geranium flower, whilst festooned with phoretic mites.
These mites are pretty common, and they spread between bumble bee colonies by attaching themselves to workers, and then dismounting into flowers visited by the bees. They then wait for the next bumble bee visitor upon which to hitch another lift.
They are able to remain in a flower head for up to 24 hours, and it takes just 3 seconds for a mite to hop onto the bee's proboscis (tongue) or legs, and climb up onto the bee's body (Schwarz & Huck 1997).
Although a bumble bee can continue to forage quite happily with a few mites on their bodies, indeed, I have seen bumble bees, so infested that they cannot move!
It is this type of infestation that provokes queries - i.e. how to help a bumble bee with mites.
In the image above, the bumble bee has mites, but it is not covered in them, and is able to forage and go about its business. Busy bees with a few mites should be left alone. It is thought that a few mites are unlikely to cause harm. In the nest, they feed on nest detritus, pollen and wax.
However, an infestation could potentially turn a merely commensal situation (the mite living alongside the bumble bee colony), into one potentially more hazardous if the mites become vectors of disease (Haas et al 2019(1); Benton(2)).
Goulson notes that an infested queen will be hampered in their ability to fly, feed, mate and hibernate.
So should you help bumble bees in this situation, by attempting to remove the mites?
The Bumblebee Conservation Trust advocate leaving bumble bees with a few mites alone, but they also state:
As I write in 2021, I am increasingly uncertain about trying to interfere, even if it is tempting to do so, but in any event, usually there are not enough mites on the bee to warrant taking action, and trying to remove the mites may cause stress.
Please remember that bumble bees have survived for hundreds of years without humans interfering by picking off mites. Also, please remember that bees do sometimes like to rest.
If a bumble bee is unable to move because it is heavily infested with mites, and if you manage to gently flick some of the mites away, you can then offer a little sugar water (use one spoon of ordinary sugar to two spoons of water). Do not use demerera sugar or honey. To offer the sugar water, you can add a few drops onto the work surface close to the bee, or dip a flower head into the sugar water, and offer it that way. However, if the weather is fine and you have a garden full of flowers, it is better to put the bee on a flower so that it can feed itself and gain the nutrients it needs.
Here I have a a closer photograph of the same bumble bee pictured top of the page, but if you look very, very closely, you can see the mites are slightly loose.
(1) Haas, S.M., Cardinal, S., Beaulieu, F. and Forrest, J.R.K. (2019), Mite‐y bees: bumble bees (Bombus spp., Hymenoptera: Apidae) host a relatively homogeneous mite (Acari) community, shaped by bee species identity but not by geographic proximity. Ecol Entomol, 44: 333-346. https://doi.org/10.1111/een.12706
(2) Benton, T. Bumblebees - The Natural History & Identification of the Species Found in Britain. Collins 2006. Page 144.
(3) Goulson, D. Bumblebees: Behaviour and Ecology. Oxford University Press. Page 63.
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