While humans were busy squabbling over the border between the United States and Mexico, a tiny black immigrant bee was discreetly homesteading in California. A new sighting of a Central American native bee, a member of the genus Plebeia, was recently reported in a genteel area of Palo Alto, some 500 miles to the north of Mexico.
This article first appeared in American Bee Journal, Volume 159 No 7, July 2019, pp. 769-773.
the manager of the Elizabeth Gamble Garden, an iconic public park, contacted a
company for help in removing a bee nest from the premises. On seeing the nest,
however, the exterminator sent a specimen to an entomologist who recognized the
bee as Plebeia. Plebeia is one of many genera belonging to the tribe Meliponini,
commonly known as the stingless honey bees.
this sighting, only one stingless bee colony was known to exist north of the
Mexican border, a nest that was first discovered in a Palo Alto backyard in
2013 and was being monitored by the State of California. Plebeia is a small genus of heat-loving bees native to southern
Mexico and Central America that ranges as far south as Argentina. Since the
first sighting in California, at least three other photos of Plebeia have shown up on the citizen
science site iNaturalist.org, all within a short distance of the original nest.
These recent sightings are most likely descendants of the 2013 colony.
No one knows where they crossed the border or how they got so far north. Someone could have smuggled them in, or perhaps they hitched a ride in a shipment of goods. It is also possible, though highly unlikely, they traveled on their own over the course of many years. In any case, higher than average annual temperatures no doubt played a role in their survival.
From here and beyond
in North America, we tend to pigeonhole bees into two classes, honey bees and
native bees. But that division is not accurate due to the many other non-native
species that also live here. Lists have been assembled by various
organizations, and depending on where you look and how you count, it is fairly
easy to find the names of 45 to 70 bee species that have arrived on our shores
since colonial times.
on the mathematics of reproduction, I suspect many more species have
established populations we haven’t yet discovered. Like an invasive plant, a
newly introduced bee species may increase by only a few individuals per year.
Many years may pass before the population is large enough to spread. Often, by
the time it is recognized as something unusual, the organism may have colonized
a large area.
Terminology of introductions
that move into new areas are known as adventive, but the word has several
shades of meaning. Some scientists include deliberately introduced species, but
others include only those that arrived on their own or by accident.
writers use adventive to describe species that are not self-sustaining, but need
an occasional population boost from their homeland. If an adventive species
becomes self-sustaining in its new geographic area, it is then said to be
naturalized. Other words with variable meanings such as acclimatized,
immigrant, and invasive make the subject even more confusing.
Stingless bees are not alone
the Palo Alto Plebeia bees will
naturalize is unknown, but many bee species that arrive in North America are
happy to call it home. The extreme example is the European honey bee,
deliberately introduced into Jamestown, Virginia in the 1620s. Although it
spread easily, the original population was supplemented frequently from its
homeland until the Honey Bee Act of 1922 put a halt to additional imports in an
effort to control the spread of diseases and parasites.
that, little was added to the honey bee gene pool in the Americas until the
accidental release of a small number of Apis
mellifera scutellata occurred in Brazil in 1958. Those rogues immediately
mated with the South American stock of Apis
mellifera, giving rise to so-called Africanized honey bees. Although
frequently called “scuts,” these bees are not pure A. m. scutellata, but a cross. Ironically, the cross appears to be
more scrappy than the real thing.
Africanized honey bee continues to spread farther and farther north aided by
warmer temperatures, but also by shipping of queens and packages which likely
contain genes from Africanized stock.
More recent interlopers
adventive bee from the south has settled in southern Florida and is a popular
subject with photographers. Euglossa
dilemma is a member of the orchid bee tribe, Euglossini. These bees, native
to Central and South America, are a show-stopping iridescent green with tongues
two-thirds as long as their bodies.
the females have pollen baskets on their rear tibiae much like honey bees, the
males have enlarged hollow tibiae with small openings in the side. Like bota
bottles for bees, these containers are used to store plant oils that will later
be deployed to attract females. Commonly known as the green orchid bee, Euglossa dilemma was first spotted in
Broward County in 2003 by USDA scientists who speculate a nest was accidentally
imported in a wooden object such as a crate or pallet.
has also been colonized by Centris nitida,
a large stocky bee known as the shining oil-digger. Unlike most Centris bees in North America, this one
nests in dead wood, which is probably how it got to Florida. Although not
considered a pest, it can be alarming because of its sheer size and speed.
A bull by the horns
scientists have been sharply criticized for deliberately importing a species of
mason bee, Osmia cornifrons, back in
1958. Although these bees look different than our domestic mason bees due to a
pair of horns on the face, they pollinate basically the same crops as our own Osmia lignaria. So why import them and
displace our natives?
that’s only half the story. During the introduction phase, our intrepid USDA
members failed to notice they were handling not one but two species of Osmia. While releasing Osmia cornifrons (the horn-faced bee)
into North America, they were simultaneously but unknowingly introducing Osmia taurus (the taurus mason bee).
turns out that both species have facial horns, both pollinate the same plants,
and both are spreading rapidly. Ironically, the taurus mason bee — the
accidental one — seems to be naturalizing faster and spreading farther than the
deliberate introduction. Oops times two.
I’m tattling on the USDA, I should mention another intentional introduction, Anthophora plumipes, the hairy-footed
flower bee. This species from Europe and southern China was introduced into the
United States at the USDA honey bee lab in 1980. Although it spread slowly at
first, melittologists now speculate this digger bee could spread throughout
most of North America
almost identical bee, Anthophora
villosula, the Asian shaggy digger bee, was also introduced at Beltsville,
although more recently. Both of these Anthophora
species are comfortable in urban areas where they live near homes and gardens
and are particularly fond of azaleas.
A ticket to North America
a substantial number of bee species have been deliberately introduced to
pollinate particular crops, many of our non-native bees arrived accidentally.
An early introduction, one of the few ground-nesting transplants, is Andrena wilkella, known as Wilke’s mining
bee. This bee arrived in the early 1900s, probably by ship, when soil was
sometimes used as ballast. This bee is well-established in northeastern and
northcentral areas of the United States and southeastern Canada.
you look at a list of introductions, you can see that ground-nesting bees don’t
transport nearly as easily as those that nest in cavities. Items of commerce
such as bamboo, wooden furniture, pallets, shipping crates, and ornamental
plants have all contained stowaways.
family Megachilidae comprises nearly all cavity nesting bees and represents the
majority of introductions. On the other hand, the Andrenidae, nearly all of
which are ground dwellers, rarely arrive in commerce. The Colletidae,
Halictidae, and Apidae families are represented by both types of bees and have
produced an intermediate number of introductions. Migration definitely runs in
Foreign bees and the environment
do all these foreign bees affect us? Although their interactions with the
environment are not well studied, most entomologist agree that their impact can
the positive side, many of the deliberately introduced species do a great job
of working the crops they were imported to pollinate. The alfalfa leafcutting
bee, for example, is an excellent pollinator of imported alfalfa. The bee was
introduced because honey bees are known to be poor pollinators of alfalfa.
Simply put, honey bees don’t like getting bopped on the head by the trip
mechanism in the alfalfa flower.
After several irritating encounters, honey
bees learn to avoid the hit by approaching the backside of the flower and
reaching between the petals to find the sweets. This move, known as nectar
robbing, avoids the stamens and results in very little pollination. The tiny
alfalfa leafcutter, however, seems unperturbed by aggressive flowers. A few
bumps is a small price to pay for all that pollen.
crop-specific introductions, including the Osmia
bees mentioned above, do an excellent job with fruit trees and berries. Many of
the introduced species are polylectic, meaning they pollinate many different
crops, so are thought to be an overall boon to agriculture.
The fallout from influx
all the news is not good. The most widely recognized downside from foreign bees
is competition with native bees for floral resources. In second place is their
potential ability to spread pathogens and parasites to native bees that have no
natural immunity to these novel afflictions. In addition, some of the
introduced bees specialize on what we consider invasive weeds, resulting in
increased seed set and accelerated distribution of unwanted plants. Other
worries include possible hybridization with native bee species that could cause
a shift in pollination preferences, and possible shifts in well-established
good example of an unfortunate introduction is Lithurgus chrysurus. This bee, native to regions of Europe, the
Near East, and North Africa, was discovered in 1970 in New Jersey. This bee has
two irritating habits: It specializes on invasive spotted knapweed and, like
the carpenter bees, tunnels into wooden structures to build its nest.
structural damage has been reported to barns, garages, wooden bridges, and
outdoor furniture. It is also known to colonize stacked firewood, wooden
shingles, sheds, and picnic tables. Some entomologists fear that it has the
potential to be much more damaging to wooden structures then our native
other adventive bees have earned bad reputations due to a lack of social grace.
The sculptured resin bee is known to attack native carpenter bees, coat them
with plant resin, and then steal their nests. Anthidium manicatum males are extremely territorial and can often
be seen attacking—or even killing—native bees or managed species like honey
bees. And others, such as Apis mellifera,
just seem to take more than their share.
Summer in the city
characteristic common among introduced species is their ability to thrive in
highly populous urban areas. Accidental introductions are likely to occur at
international ports in busy industrial areas. Once they arrive, the bees that
can survive in those environments do, and the rest die, which leaves a
self-selected assortment of urban-adjusted bees.
possible reason for urban settling may relate to the vast number of introduced
plants that occur in highly-populated areas. Compared to forest, prairie, or
even suburbs, cities host ornamental plants and weeds from all over the world
where they grow from balconies, rooftop gardens, cracks in the pavement, and
desiccated ballfields. The plants are eclectic and so are their pollinators.
addition, recall that most introduced bees are cavity dwellers rather than
ground dwellers. As it happens, cities are famously short on open bare ground,
but are teeming with cavities, such as holes in wooden buildings, cracks
between bricks, loose mortar, disused equipment, and overfull storage
buildings. These tiny crevices afford endless nesting opportunities for city
dwelling bees while they dine in irrigated flower boxes and city-maintained
While some bees have arrived with baggage — their homeland diseases and parasites — some have come unencumbered. Like invasive organisms of any type, if an exotic bee can escape enemies such as predators, pathogens, competitors, or famines, it can flourish and spread rapidly. In addition, predators living in the new land may reject the newcomer as a food source, simply because it is unfamiliar and not part of the usual menu.
A bee of a different color
bees — no matter how they got here — are often easy to identify among all the
natives. They often appear just a little “off,” a bit different from the
others, even those in the same genus. The introduced Osmia bees I mentioned have those horns, the Anthophora have long black hair on the middle legs, and some of the
introduced Megachilidae have unusual shapes or coloring. The sculptured resin
bee, for example, looks different from most American Megachile and so does the alfalfa leafcutter. And Apis mellifera have wing veins unlike
anything else in the entire hemisphere.
differences make sense from an evolutionary perspective. Even though these bees
are closely related, thousands of years of physical separation have allowed
their gene pools to shift in slightly different directions. In the end, they
are the same … only different.
In recent years, interest in “alternative” bees has blossomed such that previously little-known species are taking center stage. All the interest means more people are looking and discovering. As both professional and amateur bee stalkers continue to comb fields, meadows, and city parks, other adventive species will surely be found.
Special thanks to Colin Purrington of Swarthmore, Pennsylvania for his photos of Osmia cornifrons and Osmia taurus. You can see more of his nature photos at https://colinpurrington.com/
Thanks also to selwynq of Palo Alto, California, Ty Sharrow of Lehighton, Pennsylvania, and Judy Gallagher of Woodbridge, Virginia for their photos of Plebeia, Lithurgus, and Euglossa respectively.
For a worldwide
list of bee introductions see Russo L. 2016. Positive and negative impacts of
non-native bee species around the world Insects, 7(4), 69. doi:10.3390/insects7040069.
Bees Introduced into North America
The following list, compiled from various sources, shows bees introduced into North America since the 1600s. It does not include bees introduced into new areas within the United States (such as from the mainland to Hawaii) nor does it include bees introduced from one territory to another.
- Family Apidae
- Anthophora plumipes
- Anthophora villosula
- Apis mellifera
- Centris nitida
- Ceratina cobaltina
- Ceratina dallatorreana
- Ceratina dentipes
- Ceratina smaragdula
- Euglossa dilemma
- Peponapis pruinosa
- Plebeia frontalis
- Triepeolus remigatus
- Xenoglossa strenua
- Xylocopa appendiculata
- Xylocopa tabaniformis parkinsoniae
- Family Andrenidae
- Family Colletidae
- Hylaeus albonitens
- Hylaeus hyalinatus
- Hylaeus leptocephalus
- Hylaeus (Prosopis) variegates
- Hylaeus punctatus
- Hylaeus strenuus
- Family Halictidae
- Halictus tectus
- Lasioglossum eleutherense
- Lasioglossum leucozonium
- Lasioglossum zonulum
- Family Megachilidae
- Anthidium florentinium
- Anthidium manicatum
- Anthidium oblongatum
- Chelostoma campanularum
- Chelostoma rapunculi
- Coelioxys coturnix
- Heriades truncorum
- Hoplitis anthocopoides
- Lithurgus chrysurus
- Megachile apicalis
- Megachile concinna
- Megachile ericetorum
- Megachile lanata
- Megachile rotundata
- Megachile sculpturalis
- Osmia caerulescens
- Osmia cornifrons
- Osmia cornuta
- Osmia taurus