Musings...

Last Monday (18 April 2010) my fiance Paul spotted, and I fished out, a bumblebee struggling in a basin of rainwater. It hadn't been in long enough to mess up its wings, and was still strong enough to beat its wings immediately to dry them, so ordinarily it would have been a couple of minutes' pleasant work: rescuing, providing dry surfaces for walking, encouraging enough flight to restore the wings, then bringing the bee to an open flower or flowers in the sun to complete its recovery at leisure. But this bee was different.

Its back (dorsal thorax surface) was thickly covered with round tan shapes under a millimetre in size. There was a broad fringe of them along its brow (the head above eyes) and some scattered along its sides or crowded between body segments. There were many dozens of them. They looked like parasites to me, even before I saw one of them let go, crawl to a new position, then lower its head and grab on again.

I showed the mite-ridden bee to Dad, working on his fishing boat on his marine ways. Those, he said, were the things that killed his honeybees and our neighbour Laurie's. The recommended chemicals were horrible, but the non-chemical approach didn't work (screen at the bottom of the hive, for the mites to fall through while the bees walk above, and vegetable oil, smeared on a liner below, to trap the mites by sticking them to the liner paper).

I found a clear plastic box and a strip of screen (but had to stop using the metal screen because the bee kept biting it trying to get out). I put drops of both oil and water on a piece of plastic film and tried to trap mites with it, but they just clambered through the stuff. Sticky tape (clear packing tape, slightly used) rolled into a stick with sticky outside, made a good tool to brush a few mites off the bee, but the mites walked freely over (and inside) it and never got trapped. Maybe these thorny-legged little suckers are different from the infamous varroa mites. These are even tough critters to crush, though not quite as rugged as fleas. (But then, fleas are massive compared to these.)

When I took the now-exhausted bee to a flower, it eagerly scrambled aboard it -- and some of its mites scrambled to disembark onto the flower. Realising they would lurk in the petals waiting for the next bee, I picked the flower and brought it inside together with bee and passengers. The dandelion petals seem to be a favoured lurking place for these mites.

When off the bee, the creatures wander hither and yon at a steady run, just like harmless red velvet mites on the high high tide zone of the beach. But if they notice the bee, these mites bend their course toward it and duck around its feet waiting for a chance to climb aboard. They also like to hang out under objects and in the flower; the rest of the time they're on the go if not latched onto the bee. Many of them no doubt have scattered through our kitchen, but they won't find bees here, so unless they get along with spiders they won't do very well. (A tiny brown spider came hunting along the kitchen shelf, so I put it on the table to see how it would interact with the mites. I chivvied an errant mite with an eyelash so that it bumped into the spider, which turned in a flash and grabbed the mite in its jaws. Just as quickly it threw it away. Too spiky and tough? A bad taste? Did the mite bite? It lay where it fell from the spider's perch.)



Since Monday I've been playing telephone tag with an apiculture specialist from the provincial department of agriculture. I hope to find out what these mites are, and what local humans can do to make it easier for this and other bees to survive. Meanwhile, it's amazing how big a drop of honey a little bumblebee can eat. (I've given her water too.) She combs herself much more effectively now and often knocks mites off. Then she ignores them, or just moves away. She's too peaceful to think of cracking them with her jaws. If I take them away, or they wander off, their numbers keep dropping and she keeps looking better. But meanwhile what's been happening to the rest of her nest?

Maureen in Egmont, BC
(using my son's Christmas gift from his uncle, an EyeClops Bionicam toy video microscope)

Update Friday April 23:
Those mites riding the bee may have been commensal (gaining a benefit without doing harm) rather than parasite (benefiting by harming their host). Here (posted with permission) is some clarification from the bee keeping expert I mentioned.   Paul van Westendorp says:

All bumble bees (there are close to 30 species in BC) are terrestrial nesters. Unlike honey bees, bumble bees like to nest in crumbly soil rich in organic material, roots, etc. Because of the soil, bumble bees have evolved such that they have the company of an extraordinary assortment of other organisms, ranging from fungi and nematodes to spiders and mites. While the vast majority of these organisms are not pathogenic, it is amazing that bumble bees don't suffer as much as one would expect. On the other hand, it has been observed for many years that the abundance of bumble bee populations tend to go through large fluctuations from one year to the next. It appears that this is not principally caused by inclement weather but other factors also. It is very possible that one or a combination of these associated organisms may be partly responsible for these populations' fluctuations.

Getting back to your bumble bee. The mites on the bee are likely to be pollen mites that take advantage of the pollen grains on the hairs of the adult bee. The cuticle of the bee (i.e. the hard skeletal plates of the bee's body) are probably too thick for these mites to penetrate. I don't know this for sure as I don't know the identity of these mites. I am not an expert on this highly specialized field of the Acaridae but it is likely to be nothing more than pollen mites. As such they are typically opportunistic feeders and don't pose a threat to bumble bees and other organisms.

Labels: arthropod, ecology, nature