There are a handful of places around the world
with very high bumblebee diversity. Utah does not lead the list. In fact, it
isn’t really all that noteworthy. In America, other mountainous states, like
Montana and Colorado, have more species (Wilson et al., 2022). European nations
also tend to have a higher diversity. And the mountains of Asia lead the list
(Williams et al., 2010).
But Utah bumblebees are unique in at least one
way. There are more orange-banded species here than anywhere else (comparing
places of comparable size). This orange-banding refers to the top side of the
visible abdomen where the coloring is strikingly visible from above. Along with
the typical bumblebee colors of yellow, white and black, we have 9 species that
have orange banding. The color is not always in the same place. Sometimes it is
wide and located noticeably between thin yellow bands. Sometimes it is narrower
or shows up at the end of the abdomen. Sometimes only on the sides. But these 9
species represent 90% of all the orange-colored species in America.
It would be nice if we could somehow make a
connection between this coloring (of bees) and the beautiful red-rock geology -
where many of these bees live. The colors are often similar, but the connection
is probably far-fetched. Our bumblebees (of any color) tend to nest in (or on)
the ground and visit flowers of many colors. They seem to completely ignore the
orange erosional landscape all around. It is more likely that the orange theme
developed for the protection it offers and not, as my wife Kathy would say,
because they are color coordinated.
The natural world is full of species that
resemble each other (we call this mimicry) - or that resemble details of the
places they live (we call this camouflage or protective resemblance). When I
was in school, I learned that monarch butterflies are bitter-tasting to birds
because they feed on milkweeds that are also bitter (and that have heart
poisons in their bodies from the milkweeds). I also learned that viceroy
butterflies, even though they are not bitter, are also protected because they
look like monarchs and the birds are unable to tell them apart.
This is classical mimicry where one species is
poisonous and one is not. But it is only one kind of mimicry. We call it
Batesian mimicry (after Henry Walter Bates who first noted it in butterflies in
Brazil). Our bumblebees don’t follow this pattern. As far as we know, each of
the orange-banded species is capable of stinging a predator. The word we use
for this form of resemblance is Müllerian mimicry (named after Fritz Müller),
where all of the species are “honest” about their warning colors. None of the bumblebees
are free riders.
Scientists believe that the orange banding
evolved as a protection against predation. Bright reds and oranges are commonly
seen in species that have chemical or mechanical means of defending themselves.
Predators tend to leave them alone. With Müllerian mimicry each of the species
contributes to the overall message.
In one of our species (the Vancouver Island
Bumblebee) the orange banding is evolving right now. This species is recognized
by the black V-shaped area on the thorax and is a common visitor to meadows at
mid and higher elevations throughout the Western United States. Outside of Utah
it is mostly yellow and black. But here in Utah there seems to be an advantage
in having an orange-band - in having access to some of that Müllerian
protection. Here most of the populations of the Vancouver Island Bumblebee have
evolved the orange banding.
The story in Utah gets even more interesting
because we have insects that mimic the Müllerian mimics themselves. I recall
one afternoon in late June. I was working with a few students on a project just
a few miles up Cedar Canyon (east of Cedar City). We were sampling pollinators
at a beautiful meadow called Crystal Spring. There were three different kinds
of orange-banded bumblebees in the area. And we were looking for some of their
nesting sites. Then one of the freshman students said she had just caught a
bumblebee that she didn’t recognize. It was in her insect net and she didn’t
feel comfortable removing it.
She was quite surprised when I told her the
insect she was holding was not a bee at all. It was a fly. It was a large
robber fly (of the aggressively predatory family Asilidae). These flies are
known to attack other insects, even catching other bees out of mid-air. The one
in the net belonged to the genus Laphria and it was colored bright
orange and yellow, and it was the same size as the bumblebees (though a bit
narrower).
A few minutes later, one of the other students
showed me yet another fly mimic. It was a hover fly (specifically a drone fly)
with the same colors and the same overall shape. Drone flies are not dangerous
- at least not to predatory birds. They have predatory larvae that eat small
soft-bodied insects like aphids. But they were certainly not (as orange-colored
adults) contributing to the so-called “ring” of Müllerian mimics. It appeared
to be a free rider - a Batesian mimic among the group of otherwise honest
mimics.
Mimicry is woven deep into the world. We find it
in the velvet coating of a bee, for sure, but also in the calling of a
mockingbird and in the banding of a snake. It can even show up in behavior and
in speech. A human child watches carefully the actions of her friends, and
mimes her way into becoming a human being.
We as a species have greatly magnified our
options. We change our clothes to satisfy a whim, with wardrobes more
convincing than a cuttlefish’s blush. We want our choices to be new and we want
them suited just for us. And yet we copy from the advertiser’s many tempting
offerings. We play with and modify our mimicry every single day.
Is the mimicry that protects a tasty butterfly
similar to our own sartorial choices? Or do we change ourselves for other ends?
The orange-banding of a bee is very much a part of its identity. It isn’t a
form of protective camouflage. The coloring is intended to send a message to
enemies. It is also a token of membership.
There is insight here and irony even if we don’t
know all the answers. We, as a species, seek for popularity and acceptance in a
brand, even as we try to be unique. Nature, on the other hand, is not concerned
with being seen unless she is out looking for a mate. Evolutionary biologists
argue that this is not different from us. But what is different is our
indecision and our many choices. Sometimes we want to be camouflaged or hide.
Other times we want to be seen. Very often we want to be a part of a group. Other
times we pretend to be other than we are. We seem to be unique as a species in
the extent of our imagination, including the many creative ways we are able to
see ourselves - and even to create ourselves.
The colors of bumblebees and humans are
beautiful and fascinating. But there is a difference between us. The colors of
a bee are inherent, that is they are genetically determined. Our decisions are
often optional even though the underlying biological needs that lead us to be
creative are not optional. They are inherent and deeply programmed needs.
Becoming who we want to become is the quest of a lifetime that requires our
creativity even as we come to understand our deeper mental and physical
realities.
And color does not change the fact that there
are many other aspects of our nature. We should not assume that membership in a
mimicry ring automatically provides immunity to bees. Much to the contrary.
Bumblebees have a lot going on in their lives and the challenges of survival
come from a lot of different directions and at different times of the
year.
Winter is one of their biggest challenges. It is
also one of their most important competitive advantages. Bumblebees are most
abundant and in greatest diversity on mountains and in the north. There are a
lot of pollinators in the cactus gardens of the Southwest, hundreds of
different kinds. And most of them are bees, just not bumblebees. But things
change as you go up a mountain. The pollinators are not the same species.
Bumblebees gradually become more important. If you go high enough, even the
flies become more important to flowers than most bee species.
Scientists have known this for a long time. It’s
one of the reasons that bumblebees are so endearing to those of us that love
mountains - and to those of us that live in mountainous regions. It’s easy to
just assume that bumblebees are the thick furry grizzlies of the insect world.
They enjoy the summer meadows and simply hibernate through the cold months of
the year. But this picture is in need of nuance.
Late fall and winter are the seasons of
bumblebee death. They do not survive the winter by huddling into groups like
honey bees in order to keep from freezing. Very often the smaller workers just
succumb to the cold. It is only the larger queens that survive into spring. And
it is their ability to generate and insulate heat with their large thoracic
muscles that give them this advantage. If they are unlucky or otherwise choose
poor overwintering sites, even the queens may not survive. Color has nothing to
do with it.
And then there are the parasites. In Utah, these
tend to be other bumblebees. The most commonly encountered species has the
rather lengthy name of Indiscriminate Cuckoo Bumble Bee (Bombus insularis).
Some authors call them social parasites. Sometimes they are called
kleptoparasites. They don’t feed on the bodies of other bees, instead they
steal their food and lay eggs for other bumblebees to take care of and
raise.
Sometimes they will fight for the food and these
fights can be lethal. They always cause stress among the host bees. I have
hiked on hundreds of Southern Utah trails over several decades and, during some
years, I find this parasitic bee to be quite common. It has a black abdomen
with a pale white fringe on its back end. Unlike other bumblebees that have a
special hair-free space on their hindlegs for storing pollen, cuckoo bumblebees
don’t bother with the task of gathering this protein-rich food for their brood,
and they don’t have this anatomical storage capacity. They just follow other
bees into their nests, fight anyone who stands in their way and then lay eggs
that the host bees take care of. I am always tempted to get rid of some of them
in order to give the other bees a break. Sad to say, I sometimes give in to
temptation.
Other parasites and pathogens can be a problem
to bumblebees. Scientists worry about a process called spillover. This happens
when a disease jumps species. In America, there are a handful of these harmful
organisms that already afflict honeybees or imported bumble bees - especially
in agricultural areas. Ivan Meeus et al. (2011) have compiled a list of
parasites and pathogens that are likely candidates for spillover events into
populations of native American bumblebees. These organisms include six kinds of
viruses, two fungal pathogens, two arthropods, two euglenozoans, and a species
of Apicomplexa.
Almost every year we learn of bumblebee declines
due to these harmful organisms. Most of the time the problems are caused by
human ignorance and negligence. And most of the time, the problems occur around
large greenhouse operations or in blueberry farms. This doesn’t really apply to
Utah and we do not suffer from these problems as much as other places because
we live in a high desert and/or mountainous state that is largely free of
bumblebee diseases. Two species that are suffering declines in surrounding areas
(the Western Bumble Bee and Morrison’s Bumble Bee, for example) are holding
their own in Utah.
Nature is dealing with our changing world in a
lot of different ways. And one of her greatest challenges is the increased rate
of these changes. The changing colors of the two-form bumblebee in Utah has
likely been happening for thousands of generations. The sudden appearance of
diseases and of changing habitats is happening in just a few.
When I watch a Utah meadow and see the evidence
of a world developing on its own - becoming so colorful even as it remains
interdependent - I wonder why our own creativity can be so harmful. Why do our
greedy and desperate natures prevail so often when we have the capacity to
become orange with the bees? Maybe part of the reason is that we have never
discovered all the different forms and how we are not so different after all.
Maybe we should dress more like the bees.
If you ever happen to visit our state (or even
if you live here and don't get out much) pay attention to our big furry
bumblebees. They are still here - lots of them - and they keep protecting our
world even as they work together to protect themselves.
References
Ghisbain, G., Lozier, J. D.,
Rahman, S. R., Ezray, B. D., Tian, L., Ulmer, J. M., ... & Hines, H. M.
(2020). Substantial genetic divergence and lack of recent gene flow support
cryptic speciation in a colour polymorphic bumble bee (Bombus bifarius)
species complex. Systematic Entomology, 45(3), 635-652.
Heinrich, B. (2004). Bumblebee
Economics. Harvard University Press, Cambridge, Massachusetts.
Meeus, I., Brown, M. J., De
Graaf, D. C., & Smagghe, G. U. Y. (2011). Effects of invasive parasites on
bumble bee declines. Conservation Biology, 25(4), 662-671.
Plath, O.E. (1934). Bumblebees
and their Ways. Macmillan Company, New York.
Williams, P. H., Ito, M.,
Matsumura, T., & Kudo, I. (2010). The bumblebees of the Nepal Himalaya
(Hymenoptera: Apidae). Insecta Matsumurana. New series: journal of the Faculty
of Agriculture Hokkaido University, series entomology., 66, 115-151.
Wilson, J. S., Pan, A. D., Alvarez, S. I., & Carril,
O. M. (2022). Assessing Müllerian mimicry in North American bumble bees
using human perception. Scientific Reports, 12(1), 17604 (9
pages).