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Female Valley Carpenter Bee (Xylocopa varipuncta) on California encelia
Mother Nature's Backyard Garden |
We
love the insects in Mother Nature’s Backyard. In fact, our gardens are specifically
designed to attract many types of pollinators, from hummingbirds and bees to
moths and flies. But each spring we particularly look forward to the large
bees. Just recently we saw one of our
favorites, a female Valley Carpenter Bee (Xylocopa varipuncta). We thought you
might enjoy learning about this interesting native pollinator. Its scientific name is pronounced: ZIE-low-co-puh vair-ee-PUNK-tuh).
Valley
Carpenter Bee is the largest native bee in California. It belongs to the genus Xylocopa (the Carpenter Bees), a genus
with approximately 500 species world-wide.
In general, the Carpenter Bees are large, wood-nesting bees found in a
variety of habitats, from the sub-tropics to temperate woodlands.
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Female Valley Carpenter Bee (Xylocopa varipuncta) -
busy in spring |
The
Valley Carpenter Bee is native to Southwestern U.S. from California to Texas
and south into Northern Baja California, Mexico. Its
common name honors California’s Great Central Valley, where this species does,
indeed, occur. But this bee flies
throughout the California Floristic Province (W. of the Sierras) and is fairly
common in S. California. Xylocopa varipuncta lives where ever
there is wood for nest-building. In the
wilds, this is most commonly in the lower elevation oak and riparian woodlands
of California’s valleys and foothills.
But the species is also seen in urban gardens, particularly those with
native plants.
The
species Xylocopa
varipuncta is the most sexually dimorphic of all the Xylocopa species. You may have seen the males and females and
believed them to be separate species.
Females are large (15-25 mm; ½ to 1 inch), shiny black bees. They are relatively slow flyers, although
they don’t spend long periods on individual flowers. But if you wait patiently, you can get good
pictures of this large bee.
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| Female Valley Carpenter Bee (Xylocopa varipuncta) |
The female Xylocopa varipuncta looks like a large, black bumblebee with
amber-colored wings. The body color is
black: black head, thorax, abdomen, legs and antennae. The female body is shiny, but closer
inspection shows that legs, thorax and posterior abdomen are actually quite
hairy. In fact, females can pick up
quite a load of pollen, making them look superficially like a black and yellow
bumblebee (see below).
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Female Valley Carpenter Bee (Xylocopa varipuncta) on
Arroyo Lupine. Note yellow pollen. |
Male Valley Carpenter Bees are
smaller, very hairy and a striking golden brown color. They also have amazing
pale green eyes - there is no other California bee like them. They are sometimes called ‘Teddy Bear Bees’ because
of their resemblance to the childhood toy.
In fact, the males can be aggressive to other bees, but are quite
harmless to humans; only the females can sting (and then, usually only when you’re
harassing them).
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| Male Valley Carpenter Bee (Xylocopa varipuncta) |
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| Curious male Valley Carpenter Bee (Xylocopa varipuncta) |
The males have been difficult for us
to photograph. They are shy creatures
that are almost always in motion. We finally managed to photograph of one (above). For more good photographs of both
males and females, we recommend references 2, 3 and 4, below.
Like all of the Carpenter bees, Xylocopa varipuncta nests in cavities in
wood. The females excavate the tunnels with their stout mandibles (jaws),
usually choosing softer wood like willow or partly decomposing limbs, stumps or
logs. While not a ‘challenge’ species like
the Eastern Carpenter Bees, in urban areas Xylocopa
varipuncta sometimes nests in unpainted, untreated wood (like redwood
posts).
It takes quite a strong bee to be
able to chew through wood! We recently
drilled some ‘starter holes’ in a stump.
A female Carpenter bee has been eyeing them – perhaps she’ll stay? There are so many places for
cavity-dwelling bees to nest in a preserve like the Gardena Willows Wetland
Preserve (where our gardens are located).
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Female Valley Carpenter Bee (Xylocopa varipuncta)
checks potential nest site |
Valley Carpenter bees overwinter as
adults in these tunnels, emerging in the spring (our earliest photos in western
Los Angeles County are from early January). Then the females start to forage and the males
start to cruise. There is much work to
be done in spring. First, mating must occur. And then the nesting cavities must
be prepared and provisioned, all prior to egg laying.
Valley Carpenter Bees are
adaptable. If hollow-stemmed plants
(like bamboo or Elderberry) are available, they create unbranched, linear nests
in the stems. If not, they create or
enlarge branched nests in wood. The
branched nests usually contain 6-8 chambers; each will contain a single egg, as
well as a supply of ‘bee bread’. The ‘bee
bread’ is a mixture of pollen and nectar made by the female. It supplies food for the developing bee.
Like everything about Xylocopa varipuncta, their eggs are
large (about ½ inch long or a little more; 12-15 mm). The larvae develop in the nest, emerging as
adults in late summer (usually August). You can often see young adults nectaring in the
summer and early fall garden. The bees
hibernate in the nest tunnels over winter, emerging again in the spring or late
winter (as early as January in western Los Angeles County).
The mating behavior of Xylocopa varipuncta has been
well-studied. There are many fascinating
aspects – more than we can discuss in this short posting. We refer the interested reader to an
excellent Wikipedia posting on the species [ref. 1].
As native plant gardeners, we
encounter more insect species than do conventional gardeners. This is a good thing; it in part explains why
native plant gardens tend to be more productive and pest-free than other local
gardens. But, how do we evaluate – and explain
to our neighbors – whether a particular insect is a pest or beneficial
insect? We suggest weighing the
potential harms against the potential benefits.
The potential harms associated with
the Valley Carpenter Bee are two: 1) nesting in wood structures; 2)
stings. Given the choice, Valley
Carpenter Bees will choose to nest in dead limbs, trunks, stems and other
natural sites, rather than in structural wood [5]. They particularly avoid painted or treated
wood. So, unless you have untreated
pine, redwood or cedar, nesting is unlikely to be a problem with our western Carpenter
Bees. You might even want to provide a ‘bee
house’ or pieces of logs as suitable alternative nesting places. And as to the stings, the females are really pretty
docile. They’ll only sting to protect
themselves; given the choice, they prefer to avoid you.
As to the services Valley Carpenter
Bees provide? We see at least three: 1)
pollination; 2) recycling dead wood; 3) human enjoyment. The second service is most important in
natural settings. In Preserves, parks and other natural areas, cavity-builders
help begin the process of breaking down old wood. This is an extremely
important service – but not much observed in most gardens.
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Female Valley Carpenter Bee (Xylocopa varipuncta) pollinating
Tansy phacelia (Phacelia tanacetifolia) |
Valley Carpenter Bees are important
and efficient pollinators. They can
regulate their body temperature [1], allowing them to fly in temperatures both
cooler and warmer than other pollinators.
Their hairy bodies allow them to pick up plenty of pollen and transport
it to other flowers. They are also capable of ‘buzz pollination’ – literally shaking
pollen from the anthers by vibrating their flight muscles.
Studies have shown that Carpenter
Bees are more effective pollinators than European Honeybees for such varied
plants as Passion vine, cotton, tomatoes and melons. So we should welcome them into our gardens, and
provide them sources of nectar from early spring into fall.
Nectar
is the primary source of food and water for adult Xylocopa varipuncta. Obtaining nectar is easy from many flowers. But some good nectar sources (including
Manzanitas, Penstemons and other tubular flowers) present a real challenge for
large bees. Nectar is located deep
within the floral tube, accessible only to those small enough or possessing a
long tongue. This ensures that only the right creatures – those who actually
perform the service of pollination – can access the nectar.
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Female Valley Carpenter Bee (Xylocopa varipuncta) -
'stealing' nectar from Manzanita |
The Valley Carpenter gets around this
problem by cutting a slit in the floral tube and ‘stealing’
the nectar, without picking up any pollen in the process (see photo above). These bees even pierce nectar-less flowers,
possibly obtaining water, minerals or other chemicals from the plant sap [6]. So yes, these guys can be (adorable)
thieves!
And
that brings us to the last benefit of Xylocopa varipuncta in the home garden; the enjoyment we get from watching
these interesting creatures. Carpenter
bees are large enough for all to observe.
Even the very young and the octogenarian can enjoy their antics. Many a future biologist has been enthralled
by garden bees and other insects.
In fact, there’s much still to be
learned about these bee’s behaviors. That’s the wonderful thing about insects:
they’re all around us, yet they remain surprisingly un-studied. Perhaps you, your child or grandchild, sitting
in your garden, will discover something important. All you need is time, a pair of binoculars (or
good eyesight) and a garden that provides for our native pollinators. What a bargain!
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We encourage your comments below.
If you have questions about Duskywing butterflies or other gardening
topics you can e-mail us at : mothernaturesbackyard10@gmail.com
