Featured Post

Butterfly Gardens

Tiger Swallowtail nectaring on Purple Sage ( Salvia leucophylla ) Butterflies are among the most attractive visitors to any garden.   ...

Saturday, April 29, 2017

Valley Carpenter Bee – Xylocopa varipuncta


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. 
 
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.

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).
 
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).

The males have been difficult for us to photograph.  They are shy creatures that are almost always in motion. We’ll keep trying, and post photos when we get some.  For 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). 

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. 

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.
 

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!

 
 


____________________

 







 

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

 

 

No comments:

Post a Comment