Caught in the Act
The Briar Silky Oak (Musgravea heterophylla, Proteaceae) is growing well. It was only about a foot tall when I got it, but the summer heat and rain have given it a fillip. It is now three times taller, and each new leaf is 18 inches long. With its combination of colours — bright green, rust, and warm grey — and its sculptural shape, Musgravea is a spectacular plant.
But lately, it has been more sculptural and less spectacular.
A bee has taken a fancy to the sapling’s giant leaves and is visiting daily to snip off pieces to construct her nest tucked away in the timber.
Leafcutter bees (Megachile) are found in warmer areas worldwide. Megachile is a diverse genus with 1,500 species, of which about 150 occur in Australia. When I lived in Melbourne, Golden-tipped Leafcutter Bees (Megachile chrysopyga) were regulars in my tiny garden. These handsome black and white bees sported ginger tops and tails, and buzzed single-mindedly around the fan flowers (Scaevola aemula, Goodeniaceae). I don’t recall them wreaking havoc among the native plants at my place, but I’m sure they got stuck into the neighbours’ ornamentals.
Yesterday morning — in a rare moment of good timing — I was outside with the phone when a leafcutter flew in. I had seen the bee’s handiwork, but had yet to get a good look at her. She took a while to select her leaf, but once she had made up her mind, the time between first snip and flying away with the prize was less than 15 seconds. Busy and efficient.
But what species? This is where things got confusing. I initially identified the bee as Megachile mystacea, which was described by Johan Fabricius in 1775 (as Apis mystacea). But there is another species, very similar in appearance, which had long been mistaken for Fabricius’ mystacea. It was unnamed until Michener described it in 1962. He called it M. mystaceana and made it the type species of Callomegachile, a new subgenus of Megachile.
But how to tell them apart? It’s all in the number of teeth on the jaws, apparently. Megachile mystacea is a true leafcutter furnished with sharp secateurs, whereas M. mystaceana is a resin bee and has blunt pinking shears. Like leafcutters, resin bees also take pieces of leaves to cap their nests, but they are slapdash about it. The bee in my garden was anything but slapdash. So on the basis of that behaviour, I decided what I had encountered was Fabricius’ species.
It’s an inexact science!