The Magnificent Megachile pugnata, the Pugnacious Leafcutter Bee

Megachile pugnata (female) on blanket flower (Gaillardia aristata)

The world of bees is a diverse one for sure, but the full scope of its diversity can be elusive to the casual observer. The differences between species are often so small to see that at best we can only distinguish genera in the field. Only occasionally comes around a bee with such a remarkable characteristic that makes it unmistakable to identify. The pugnacious leafcutter bee (Megachile pugnata), with its outsized mandibles, is one of those.

Megachile pugnata (female) in portrait

I had my first sighting of the bee back in 2018 when a single female spent a day in my garden and never returned. I recall it had a fondness for mexican sunflower (Tithonia), and was way larger and much more colorful than the average leafcutter bee. Quite an impression it made, but I barely had a chance to learn about it. 2019 came and went without a single sighting. It seemed like my visitor was a rare fluke.

Then the 2020 garden season arrived. Stay at home orders provided the opportunity to tend flower beds like never before, perhaps doubling the floral resources from last year. The dramatic results attracted a flood of new diversity. Among them were three female pugnacious leafcutters that showed up on July 22nd and stayed until August 25th. They found my bee hotel and produced 11 nests in Phragmites reeds and one nest in an old piece of driftwood.

Megachile pugnata peering out of a Phragmites nest reed

The same nest as above, sealed off after completion

Note the green appearance of the nest cap when fresh.

I got to know them quite well in the month they graced my garden. They had a fondness for blanketflower (Gaillardia aristata) and bull thistle (Cirsium vulgare). I also saw them frequent a large-flowered Rudbeckia hirta cultivar. Surprisingly, they also spent a good amount of time visiting apple mint (Mentha suaveolens), which is not a composite flower like the others.

Megachile pugnata on Cirsium vulgare

I also tracked down where they were doing their leaf cutting. It turned out a large patch of fireweed was providing that service. The bees would most often visit in the evening just before sunset to make multiple clippings from these plants which were about 100' from their nests. They would also gather sand and minute pebbles from the ground below the fireweeds that can be seen in the nest cap image above. In the video at the end of this post there are a few seconds of footage showing sand collection.

What was intriguing to me is when the fireweed leaves were chewed, they would start developing red spots on them. Unchewed leaves would stay a tidy green. I found their handiwork so interesting that I pressed and framed three of the leaves to display on my office wall.

Fireweed leaves (Chamaenerion angustifolium) leaves chewed by Megachile pugnata

These bees were found in my garden in western Washington State, but they range through much of North America north of Mexico. Plant some blanketflower and put up a mid-summer bee hotel with roughly 6-8 mm wide reeds and see if they show up in your garden.

Next season's bees. My 11 capped off nesting reeds

Here's a video to see them in action.