Megachile angelarum: a bee in a pea

Early this past spring, my friend Nancy told me about a patch of everlasting pea (Lathyrus latifolius) growing alongside the sound, just across from the port of Olympia. Then she linked me to a colorful gallery of bees and other pollinators she found there. Intrigued, I packed my camera and headed north.

The pungent smell of low tide and the cheery twinkle of sun on water made me feel at home. The patch, sporting a zillion shades of pink, looked like it was planted for bank stabilization or weed control, although I don’t actually know. The flowers were gorgeous against the blue of the water and they trembled with activity.

One of the bees I kept seeing was a little leafcutting bee, quick, agile, and hard to photograph. It wasn’t one I knew, but smaller with only a subtle arch to its back. Once I got a decent photo, I sent it into BugGuide.

The trouble with bee I.D.

Now, here’s the thing I don’t understand about bee identification. When you use one of the definitive reference books like Michener’s Bees of the World, you soon get bogged down in the dichotomous keys. In short, you learn that you can’t possibly identify bees to species if you don’t dissect and closely scrutinize their penis and mouth parts.

Yes, I can do that. Yes, I have the equipment and the know how. But do I want to? That’s the real question. Personally, I want the bees to live. I want to photograph them doing what comes naturally. I have no interest in bees stuck to a pin or shredded to bits.

It’s pretty easy to classify bees into a family, and not too difficult to place them in a genus. After that, all bets are off without one of those wretched dichotomous keys. Considering that, I just take the picture and send it to the experts.

But here’s the irritating part. The experts glance at the photo and say, “That’s a Megachile angelarum.” What? What am I missing here? No one can see its…er…privates from the photo. It’s not pornography, it’s just a bee.

I suppose if you are extremely familiar, you know it when you see it. If you are familiar with horse breeds, for example, you can discern an Appaloosa from an Arabian or a Lipizzan without much trouble, right? But to the uninitiated it’s just a horse.

But this Megachile angelarum was frustrating. To me, it was a nondescript black bee. There are thousands of other equally nondescript black bees out there, so why does this one have this name?

Searching for clues

For many years now, I’ve been thinking there must be clues other than the ones they list in books, little secrets the experts don’t share. So I decided to take action. With my photos in hand, I began to comb through references, determined to find a way to separate this bee from the others. And this is what I found.

I was initially correct about the family, Megachilidae based on wing veination (two sub-marginal cells) and the abdominal scopa. But I was wrong about everything else, even the genus.

Leafcutters that don’t cut leaves

The genus Megachile contains the leafcutting bees and is often referred to as the leafcutting bee genus. But as it turns out, my bee does not cut leaves or petals. In other words, it is a non-leafcutting leafcutting bee. This was surprising to me due to the condition of the flower patch: the everlasting pea petals were not lasting at all due to an excessive petal harvest.

Instead of leaves and petals, my cavity-nesting bee collects gums and resins to build its nest. Like other bees in the same subgenus, Chelostomoides, this bee doesn’t have mandibles with the sharp cutting edges found in other Megachilids. That’s mother nature for you—if you don’t need sharp teeth, you don’t get them.

Like other members of the subgenus, this species can be trap-nested into tubes. The tubes can then be harvested and moved around to where next year’s pollinators are needed.

It’s all in the abdomen

Even though I couldn’t see the sharpness of mandibles in my photos, I was able to see two other things—things that make the species identifiable from a mere amateur photograph.

First, the metasoma (which you learned about in a previous post) is long and narrow with roughly parallel sides. But the key is that segments T2-T4 have a deep groove running from one side to the other. These grooves are closer to the basal end of each segment and are clearly visible in a photograph.

Second, T6 (the last visible segment in a female) has a distinct turned-up lip at the very end of the bee. This is also clearly visible in a photo.

Taken altogether, the abdominal scopa, the deep groves in T2-T4, and the lip at the end of T6, you can be confident of your identification. These few characteristics, all found on the metasoma, change my nondescript black bee into a Megachile angelarum without a dissecting kit, a microscope, or a dichotomous key. This is what I was looking for.

A red herring in the field of flowers

All the missing petal parts in the field of flowers were a red herring. When I went back through my other photos, I found plenty of western leafcutting bees (Megachile perihirta) and alfalfa leafcutting bees (Megachile rotundata) that were probably responsible for the destruction. My M. angelarum were little “angels,” leaving all the flowers complete. I love mnemonic devices.

In case you’re wondering, the honey bees were out in force as well and seemed to love the everlasting peas. They shared the flowers with many species of bumbles, Andrena, and Megachile.

And now for the others

I have to admit, this took a long time. I had to read long obtuse descriptions of bee parts (and look up lots of esoteric words) before I could connect what I was reading to what I was seeing in the photos. I had to eliminate the identifiers I couldn’t see, and select only those characteristics that I might be able to see in a field photo.

My goal is to do this for more species in the future so more people can begin to identify bees.

Rusty
Honey Bee Suite

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