A Long-horned Bee: Subgenus Synhalonia

Photo of a male Synhalonia warming up for flight
A male Synhalonia warming up for flight
Longhorned Bee
Longhorned bees in the genus Eucera are active in the spring months of March and April

Long-horned bee species that are active in the spring to early summer are in the genus Eucera. Synhalonia is the only subgenus of Eucera present on the North American continent. Synhalonia comprises 55 species, with most of them occurring in the western states. The three bees featured here might be of the same species, but I was unable to identify them beyond the subgenus.

With its mandibles, a male Synhalonia grips a filament of a Coast Morning Glory

The colloquial “long-horned” descriptor refers to the very long antennae on males in the genus Eucera. When I spot a bee with such impressive headgear resting, as each of these bees were, within the throat of a Coast Morning Glory, I can be confident with respect to genus and gender identification.

I found one Synhalonia just below the summit of Elliott Peak, in the Conejo Canyons / Western Plateau open space. To find such a perfect creature tucked inside a flower is primarily luck, but it also helps to know when and where to look. Bees that take shelter in flowers spend a significant portion of their short lives resting in a kind of stasis or bee sleep.

The bee is cold-blooded and when the morning is cool, it is not able to flee. A flower provides good protection from predators and is usually stocked with food. Male native bees do not build or live in nests. Across genera, they rough it in various ways, clinging to a flower’s filaments or anthers, camouflaged upon the disc center of asters or sunflowers, anchoring themselves on stems with their mandibles. Sometimes several of them gather together on or within a communal same stem or flower. Some male bees hide inside of flowers waiting for a foraging female to visit. Others go to nests where they sense that females are emerging and, strictly from this human female’s point of view, make a right nuisance of themselves.

This cycle: How long has it endured, how many times repeated? Observing a bee following a well-worn evolutionary path may feel like a gift to me, but it was not meant for me nor for any one of my kind. This bee’s ancestor was doing the exact same thing one spring day a thousand, tens of thousands of years ago, or more.

I am irrelevant to what this bee requires, except to the extent that I might interfere with, or protect, or ideally, make an effort to restore its habitat. The bee, however, is relevant to many living things, to the plants it pollinates, to diverse predators and parasites, to the bacteria that live in its gut and the bacteria that break down its component parts after death and thus, to soil renewal, to the continuation of its own and interdependent species.

One thousand years back is not too far to still be able to imagine what the world around us might have looked like: When there were no freeways, or fences, or guns; no water treatment plants or neatly tied dog waste bags left behind for the dog poop fairy; no petroleum-derived, “disposable” but not biodegradable face masks, no used tissues discarded for some imaginary clean-up crew to sweep up.

Average life span was a lot shorter for us back then, but it was still so much longer than a bee’s life cycle.

I suggested the genus Eucera when I entered my observations in iNaturalist. iNaturalist is a website where people share their observations and identifications of organisms in world around us. iNaturalist curators are subject matter experts who review observations to make sure they are taxonomically correct. They share insights and provide guidance to “citizen scientists” like me.

I first learned of the subgenus Synhalonia when a curator identified one of my Eucera observations to the subgenus, in February, 2021. For quite a while after that, I remained unaware that for spring flyers, this was the only Eucerine subgenus of long-horned bees in North America. Or was it? While researching the topic for this post, I found out about a possible exception: Protohalonia. The research paper I reference here suggests, I think, that three species grouped under Synhalonia be assigned instead to a separate genus or subgenus, but the paper’s content goes well beyond my scientific parsing ability, and it seems likely that this proposal is still under discussion by experts.

Most of my bee observations receive the benefit of an expert’s scrutiny. John S. Ascher, is a professor and researcher with the Department of Biological Sciences, National University of Singapore. He specializes in the study of bees and wasps and he curates observations on iNaturalist.

Dr. Ascher initially suggested a species identification of Davidson’s Longhorn for one of my Synhalonia bee observations. Around the same time, I observed another native bee that looked nearly identical to me and logged it as subgenus Synhalonia. Pollination ecologist Dr. Keng-Lou James Hung suggested the species: Davidson’s Longhorn. A professor at the University of Oklahoma, Dr. Hung studied taxonomy with Dr. Ascher. In fact, the two collaborate on research projects and journal articles. They were two of the four co-authors of a recent research article detailing the results of their study of the joint impacts of drought and habitat fragmentation on native bee populations in San Diego.

After some time passed, Ascher and Hung retracted the species identifications. The reason for this was that Ascher took another look at physical specimens. His reanalysis revealed some detailed features that did not support identification to the species level, specifically:

clypeus looks protuberant and extensively yellow and pygidial plate not golden

Ascher, John S., Comment on iNaturalist observation, July 2021

The clypeus is located about where a nose would be, if a bee were a human being. The pygidial plate, if present, is a small v- or u-shaped protrusion located at the end of the last dorsal segment (terga). Some bee genera lack the pygidial plate. If bees were bobcats, one could call it a tail, although it does not serve the function of tail. I wondered if it might be an evolutionary remnant of a part of the anatomy that once was, but no longer is, functional or required.

I had no luck finding information to confirm or refute my theory that the pygidial plate was an evolutionary ghost. I finally sent a message to Dr. Ascher to ask him about it. His response:

Females use the plate as a trowel for nest building. In males it may be vestigial (like male nipples). Or, as you note, it may be there for our identification convenience.

Ascher, John S., Email via iNaturalist portal to Sherrie Felton, 9 February 2022.

Whatever its original purpose was (in males), the pygidial plate did not develop for our identification convenience. Was Homo even sapient back then? I could be misinterpreting the nuance here, but perhaps Ascher was having a bit of fun. I had mentioned reading that the plate can help with species identification. It was both amusing and absurd to think that the pygidial plate evolved through natural selection for the benefit of or ease of use by our species in the present day.

In the end, both observations reverted back to the subgenus level: Synhalonia. I have learned that this is not unusual when it comes to bee identification. For some native bees, identification at the species level is difficult, even for the specialist equipped with an advanced degree, a strong understanding of the species’ physiology, a good magnifying glass, a microscope and a specimen collection. In response to my query regarding a Melissodes observation, Dr. Hung wrote:

Melissodes is one of the hardest genera to identify to species, even with pinned specimens in hand. Often times the difference comes down to the texture of the bee’s tongue, or the color of hair bands that may or may not have already worn off, or the size of the pockmarks on the bee’s thorax, or things like that. There are only a small handful of Melissodes species I feel ok with IDing from photos, and alas, M. communis alopex is not one of them. The males are even worse. My good friend Karen Wright is currently the world’s authority on Melissodes, and even she refrained from definitively IDing the males of most species when she was doing her PhD dissertation.

Hung, James, Email via iNaturalist portal to Sherrie Felton. 22 October 2020.
Photograph of a female melissodes foraging for nectar or floral oil on a Cleveland Sage shrub.
A female Melissodes forages for nectar or floral oil on a Cleveland Sage shrub. Residential pollinator garden 20 June 2020

By S. Felton

S. Felton is a writer, photographer and amateur naturalist.

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