Bumblebees and wax moth
A few weeks ago I wrote about moving a bumblebee nest from a friend’s garden. At the end of the blog I mentioned that I’d found a wax moth in the nest.
Wax moth is a native, natural predator of the bumblebee, but it’s one of its biggest enemies (apart from the human, of course). In the south of the UK it’s estimated that around 80% of bumblebee nests in gardens are predated by wax moth* – perhaps because nests under sheds, in compost bins and bird boxes are easier to find than those hidden in old mouse burrows in the countryside. Nowadays, bumblebees more commonly nest in gardens. This makes wax moth a bit more of a problem than it used to be, when there were plenty of mouse holes in hedgerows to nest in.
The female wax moth stakes out the bumblebee nest and hangs around outside for a few days to pick up its scent. Once she has done this, she enters the nest undetected to lay her eggs. These hatch into caterpillars, which start off by eating the nest debris before moving to the wax pots containing honey, pollen, and grubs. They create tough, silk tunnels, presumably to protect themselves from the adult bees. Before long the entire nest is gone, prompting the caterpillars to leave to pupate into next year’s wax moths.
When I found the wax moth in the bumblebee nest I didn’t know if I’d caught her before she’d started laying. I evicted the moth, took the bees home and hoped for the best. For two weeks the bees thrived and seemed happy in their new location. I checked on them almost daily for signs of caterpillars, but found nothing. I had got away with it, or so it seemed, and considered the bees incredibly lucky. A day, or even a few hours, later and it might have been a different story.
Then everything went quiet. I first noticed something was up as the nest appeared to shrink. I put this down to the fact that it was made from grass clippings, and that this would naturally shrink as it decomposed. But then there were fewer bees. I realised I hadn’t checked the nest for three days, so opened it only to find several wax moths ready to pupate on the underside of the roof; silken threads all over the nest.
Feeling sick, I caught the remaining bees and the queen in a glass jar and examined the nest. It was writhing with caterpillars and there were no wax pots – everything was gone. But the queen and her bees were holding on in there, angrily defending their home. I wondered if I could encourage them to carry on. I removed the caterpillars and replaced most of the bedding, then returned the bees to the box. The odds were against them but, at this stage, there was no harm in trying.
I don’t really know what’s going on now. I checked a few days later and found two new wax pots, evidence that they were starting again. I watched workers come and go. But the queen doesn’t seem to have laid any more eggs. While numbers should be increasing, they’re diminishing. The queen is just down to two workers now. If she doesn’t make any more soon it’s curtains.
*Bumblebees: Their Behaviour and Ecology, by Dave Goulson
