This is a guest post by our Research Associate, Elsa Youngsteadt…
But today, I walked past that same bench to find a whole new lively scene. Taking over from the bees (whose nesting season is winding down) was a swarm of sleek, black wasps with shiny blue wings and a bold, creamy markings. They were Monobia quadridens, a member of the group called mason wasps.
M. quadridens is, in fact, well known for nesting in abandoned bee holes, and any other convenient cavity will do, too. (If you happen to put out nesting blocks for orchard bees, you may get some Monobia, too; they’ll use tunnels ¼” to ½” in diameter.) They fill these holes with small caterpillars, which they paralyze by stinging. When the wasp eggs hatch, the Monobia larvae eat the hapless caterpillars.
Although my bench was a Monobia hotspot—I could see five or six at any moment–these wasps don’t live in social colonies like the more familiar yellowjackets or paper wasps. When it’s time to lay eggs and stockpile food for the youngsters, it’s every Monobia for herself.
And sometimes, her efforts may go to waste. The entrance of another old bee hole under the bench was clogged with ant traffic. I suspect that rather than living there, the ants were raiding whatever the resident bee or wasp had originally put there, perhaps the caterpillars. I didn’t catch the ants carrying anything I could actually identify, though, so I’ll stop there before they accuse me of libel.
Although I was all up in these wasps’ business, and a couple of them came and hovered in my face in return, nobody really threatened to sting me. If they’d been paper wasps, I would have been zapped for sure, so I’d rank them on the not-very-threatening end of the wasp spectrum. In fact, given their fashionable looks and their inclination to clean up pesty caterpillars, I hope they someday move into my very own porch. The carpenter-bee holes are waiting!