Yellow-faced Bumble Bee (Bombus vosnesenskii)

Yellow-faced Bumble Bee (Bombus vosnesenskii) approaches
Purple Sage (Salvia leucophylla)

The western United States is home to many unique and useful insects. Regional gardeners are starting to appreciate the importance of native pollinators, in part due to the activities of National Pollinator Week (the 3^rd week in June).  To learn more about pollinators in general see our June 2013 posting (http://mother-natures-backyard.blogspot.com/2013/06/life-friendly-gardening-planning-for.html).

The larger insect pollinators are among the more interesting visitors to S. California gardens.  One of our favorites is the Yellow-faced Bumble Bee (Bombus vosnesenskii).   This large native bee can be seen from spring to fall in west coast gardens from British Columbia, Canada to Baja California, Mexico.   In our garden, we most commonly see them from June through August.

Bumble Bees are true bees belonging to the genus Bombus. There are around 250 species worldwide, with ~40 native to the Western United States.  Bombus species are notable for their large size, hairy bodies and ability to fly in cold, damp weather.  They are generalist pollinators (visit a number of plant species) and live in colonies with one or a few breeding Queens.   They collect both pollen and nectar and are equipped with pollen baskets on their hind legs.



Female Yellow-faced Bumble Bee (Bombus vosnesenskii) - front view 
on Yarrow (Achillea millefolia)

Female Yellow-faced Bumble Bee (Bombus vosnesenskii) - rear view 
on Yarrow (Achillea millefolia)

 

Yellow-faced Bumble Bees are large – ½ to ¾ inch (1.5 to 2 cm.) long - and their bodies and wings are mostly black.  They have a fuzzy yellow head, including a yellow ‘head pile’ on the thorax just behind the actual head (see above) and a single yellow stripe on lower abdomen (males have a partial second stripe).  You can see more pictures at: http://www.discoverlife.org/20/q?search=bombus+vosnesenskii.  

While Bombus vosnesenskii is the most common bumble bee in local gardens, it can be confused with other native Bombus species including B. caliginosus, B. californicus,  B. occidentalis and B. vandykei.  The California Bumblebee (B. californicus) is far less common and has a black face.  The others are more likely to be found in the local mountains (B. vandykei) or on the central or northern coast.   For a complete guide to western U.S. Bumble Bees see: http://www.xerces.org/wp-content/uploads/2008/09/Western_BB_guide.pdf

 

Female Yellow-faced Bumble Bee in early spring

 

 Like all bumble bees, Bombus vosnesenskii colonies contain a breeding female (the queen), non-breeding female workers and some breeding males.  The queen is the largest; she may be up to ¾ inch long while workers and males are usually about ½ inch.  Males and females look slightly different. Males have an additional yellow stripe on their abdomen.  They have longer antennae and no pollen baskets.

More importantly, female queens and workers have a stinger, while males do not.  In general, bumble bees are not very aggressive; they aren’t pesky like wasps and they do not swarm.  However, they can sting multiple times if annoyed, most commonly when their nest is disturbed.  Bumble Bees have smooth stingers which do not detach; this allows them to survive after stinging. 

If a Bumble Bee is circling you, it most likely is just curious.  Stand still or move slowly and don’t wave your arms wildly; it will usually soon lose interest. If you are allergic to bee stings (about 0.5% of children; 3% of adults), it’s always prudent to be prepared when around bees (have an EpiPen available).    Learn more about avoiding bee stings at: https://pollinator.org/PDFs/NAPPC.NoFear.brochFINAL.pdf   

The Yellow-faced Bumble Bee follows a predictable life cycle.  Fertilized queens are the only individuals that overwinter.  They emerge in early spring in coastal S. California (as early as February in a warm year) or after the snow melts in colder climates.  Newly emerged queens can sometimes be seen visiting early-blooming flowers and flying near the ground in search of nest sites.

Yellow-faced Bumble Bees nest in the ground, but they are not excavators.  In natural areas, they usually choose old rodent burrows; in fact, the number of bumble bees correlates with the availability of such burrows.  In gardens, they may also nest under brush or compost piles, in wood piles or in loose leaf litter. If provided, they may even nest in a constructed nest box: see http://www.bumblebee.org/nestbox_plans.htm and http://www.xerces.org/wp-content/uploads/2008/11/nests_for_native_bees_fact_sheet_xerces_society.pdf

After choosing a nest site, the queen collects nectar and pollen to create a food lump (pollen ball) in the nest.  The pollen ball, which is commonly about 1 inch in diameter, provides food for the developing offspring.  She lays her eggs on the food lump, then incubates them for three to four weeks until the first workers emerge.

Warm temperatures are critical for proper development.  The queen lays her abdomen over the eggs/larvae to keep them warm.  She vibrates her thoracic muscles to generate heat. During this period, the queen only emerges if she herself needs food.  The eggs develop into larvae which feed on the food lump.    The larvae transform into pupa and finally emerge as adult female workers.  These workers help to provision and care for subsequent summer offspring.

The queen continues to lay eggs through mid-summer; she is the only individual who can lay eggs.  Her workers can be seen visiting flowers up to 2800 m (about 1.7 miles) from the nest, collecting nectar and pollen for the colony.   Some workers remain in the nest to tend the young, clean the nest and maintain nest temperature.  If the nest gets too hot, they cool it by fanning their wings near the entrance hole. 

The last eggs of summer give rise to new queens (from fertilized eggs) and male drones (from unfertilized eggs).  These adults emerge in late summer and don’t re-enter the nest. You can sometimes see drones ‘sleeping’ on flowers or foliage at this time of year. The males fertilize the new queens; then they and the workers die in late summer/fall.   A fertilized queen forages for a few weeks before digging a small cavity (the ‘hibernaculatum’) in which she remains dormant over the winter.   She emerges in spring to begin the cycle again.   To learn more about Bumble Bees we recommend: http://www.bumblebee.org/

 

Yellow-faced Bumble Bee (Bombus vosnesenskii) foraging on White Sage
 (Salvia apiana) in Mother Nature's Backyard

 

 

Bumble Bees like the Yellow-faced Bumble Bee are very efficient pollinators.   First, they have the ability to warm their flight muscles at cool ambient temperatures.  They transfer heat from the abdomen to the thorax (mid-section) which contains the legs.  This allows them to fly in cool, wet conditions that ground other pollinators.

Bumble Bees are generalist pollinators, visiting a wide range of flowers in their search for nectar and pollen.  Many interesting facts are just emerging about Bumble Bee pollination.  For example, the foraging pattern of Bumble Bees (crawling around in the flowers) promotes self-pollination within a single plant.  In addition, Yellow-faced Bumble Bees tend to visit a limited number of species on a single foraging run.  Why certain flowers are selected is not yet clear; it may have to do with characteristics of the nectar or pollen itself. But this pattern tends to maximize pollination between plants of the same species.

 

Yellow-faced Bumble Bee (Bombus vosnesenskii) foraging on Dune Lupine (Lupinus chamissonis)
Madrona Marsh Preserve, Torrance CA

 

 Bumble Bee’s large size allows them fly greater distances and to pollinate flowers  inaccessible to smaller pollinators.  They can, for example, land on the ‘keel’ of a lupine flower, causing it to pop open for access to nectar and pollen (see above). This is really fun to watch!  The optimal strategy for accessing the ‘goods’ varies with flower type.  You can occasionally watch a Bomus improve her technique as she tries out different strategies – a learned behavior that is not passed from one bee to another.

The fact that Bumble Bees visit many flower species makes them useful alternate pollinators in the wilds, on farms and in home gardens.  Yellow-Faced and other Bumble Bees visit both wild and domesticated plants.  They are known to be particularly good pollinators of tomatoes and the squash family (Cucurbitaceae).   Among the crop plants pollinated by bumblebees are: Prunus species (plums, cherries), citrus, apples, currants/gooseberries, blackberries/raspberries, peaches, sunflowers, beans, peppers, tomatoes, squash, cucumbers, pumpkins and watermelon. 

There is currently great interest in the agricultural use of Bumble Bees as alternate pollinators.  In fact, their commercial use is already raising ecological dilemmas.  In Europe, North and South America, where native pollinators are experiencing serious declines, Bumble Bees are increasingly employed as pollinators.  In general, commercially raised Bumble Bees are limited to a few species raised in a small number of hatcheries.  Scientists in Europe and the U.S. are calling for increased regulation of commercial Bumble Bees - and for good reasons (see http://ecowatch.com/2013/10/29/demand-protection-wild-bumblebees/).

Among the serious problems associated with commercially-raised Bumble Bees are 1) the spread of bee diseases and parasites; 2) the decline of native populations and species due to competition with introduced species.     Examples of both problems have already been documented in Europe and the Americas.   A more prudent strategy is to promote the survival of native species. 

Bumble Bees are declining world-wide.  Overall, there has been a decline in both  numbers and species since the early 1990’s; some species are even thought to now be extinct. This has prompted several organizations to take an active role in promoting these important pollinators.  To learn more see the following:

http://www.xerces.org/bumblebees/ 

http://blog.nature.org/science/2014/03/19/plight-of-bumble-bee-native-pollinators-ecosystem-services/

http://bumblebeeconservation.org/  

 

Yellow-faced Bumble Bees are among the species whose numbers and range are stable or possibly even increasing – at least for now.  The reasons for this are unclear and likely to be complex.  One thing that is certain is that Bombus vosnesenskii can live in urbanized areas, even in S. California.   This makes our gardens even more important as pollinator habitat havens.

 

There are a few concrete things you can do to promote native Bumble Bees.

 

1.       Plant their favored plants.  While Bumble Bees are generalists, they do favor some plants over others.  Studies have shown that Yellow-faced Bumble Bees occur most often in areas with a preponderance of native plants.  But they are nearly as common in places that contain a combination of native and certain non-native plants. When choosing non-native plants, choose old-fashioned, ‘open pollinated’ or ‘heirloom’ varieties if possible.    And aim to have flowers blooming throughout the Bumble Bee season, from spring through early fall.

Here are some plants to consider planting:

Trees/large shrubs: Ceanothus species, Cercis orbiculatus (Western redbud), Chilopsis linearis (Desert willow), Heteromeles arbutifolia (Toyon), Prunus species, and native/non-native Senna/Cassia

Smaller shrubs/perennials: Achillea millefolia (Yarrow), Agastache species (Giant hyssop), Asclepias (native Milkweeds), Symphyotrichum chilense var. chilense/Aster chilensis (Coastal aster), Ericameria species, native Lonicera (Honeysuckles), native Lupines (Lupinus, including annual and bush forms), Monardella, Penstemon heterophyllus, Mountain Mints (Pycnanthemum), Rosa californica and R. woodsii, Salvias (native sages).  Among the non-native plants that attract Bumble Bees are: Gentians (genus Gentiana), Borage, Lavender, Bergamont/Lemon Mint/Bee Balm (Monarda species), Rubus species (Blackberry, Boysenberry, Raspberry)

Annual wildflowers: Cirsium occidentale (Cobwebby thistle), Clarkias & Collinsia species, Eschscholtzia californica (California poppy), Gilia capitata (Globe gilia), Mentzelia species, Phacelia tanacetifolia (Tansy phacelia) & other Phacelias.

 

2.  Use pesticides sparingly – or not at all.  Bees – including Bumble Bees – are very sensitive to certain pesticides. A relatively new class of insecticides, the neonicotinoids, have been implicated in several large Bumble Bee die-off events in the U.S.  The neonicotinoids, which are chemically similar to nicotine, act on an insect’s nervous system.  They are effective insecticides, but don’t discriminate between harmful and beneficial insects. Pesticides that contain neonicotinoids include Bayer Advanced Garden Insecticides, Dinotefuran (Safari) and any insecticide that contains the following: Acetamiprid, Clothianidin, Dinotefuran, Imidacloprid, Nitenpyram, Thiocloprid, Thiamethoxam.  For more see: http://www.xerces.org/wings-magazine/neonicotinoids-in-your-garden/  

Practicing Integrated Pest Management (IPM) is a safer, greener approach to managing garden pests.  Keep plants healthy, use simple preventive measures and use chemical pesticides only as a last resort.   To protect pollinators, never apply pesticides to blooming plants.  For more see: http://www.xerces.org/pesticides/

 

3.   Leave space for ground-dweller’s nests.  Ground-dwelling pollinators need bare ground, brush piles and areas covered by loose leaf litter.  They cannot nest under a thick layer of mulch.  Consider leaving the ground around mature shrubs un-mulched.  Tuck garden trimmings beneath/behind shrubs where they can decompose naturally while providing nest spots for beneficial insects.

 

4.    Provide nesting materials.  Bumble Bees need loose, dry material for their nest.  An easy way to provide is this to plant native bunch grasses or ornamental grasses. Leave some of the old, dry leaves each year for birds and insects to use as nesting materials.  

 

Learn more about how you can help promote native Bumble Bees at:

Conserving Bumble Bees:  Guidelines for Creating and Managing Habitat for America’s Declining Pollinators.

http://www.xerces.org/wp-content/uploads/2008/10/agroforestrynotes34-bee_nests.pdf

 

More extensive resources on Bumble Bees can be found at:

http://www.pnas.org/content/early/2011/01/03/1014743108.full.pdf

http://www.montana.edu/burkle/publications/NorthAmericanBumbleBeeSpeciesConservationPlanningWorkshopFinalReport.pdf

Moving a hive - http://homeguides.sfgate.com/rid-bumblebees-grass-87348.html

 

 

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We encourage your comments below.   If you have questions about Yellow-faced Bumble Bees or other gardening topics you can e-mail us at :  mothernaturesbackyard10@gmail.com

 

 

Plant of the Month (June) : California buckwheat - Eriogonum fasciculatum

California buckwheat (Eriogonum fasciculatum) in foreground

 

The buckwheats (genus Eriogonum) are among the most important summer-flowering plants in S. California gardens.  In a typical year, the period from May through October is replete with their beauty.  Beginning with the California, Conejo and Red buckwheats, transitioning into the giant St. Catherine’s lace and ending with the Coastal/dune and Ashy-leaf buckwheats, the Eriogonums span the seasons with floral, seed and foliage color.   Our hot dry winter and spring have confused many plants this year.  But true to form, California buckwheat is a standout in our June floral display.

California buckwheat has a wide geographic distribution compared to other local  buckwheats.  It grows from California, Utah and Arizona in the north to northern Mexico and Baja California, Mexico, in the south.  There are at least four recognized varieties.  Two of them (varieties fasciculatum and foliolosum) are native to western Los Angeles County, including the Palos Verdes peninsula and the lowland areas of the old El Segundo dunes (coastal area from El Segundo south to the Palos Verdes peninsula).   

The species grows in a number of plant communities including Chaparral, Coastal Scrub, Coastal Areas, Desert Chaparral,   Oak and other Woodlands and Grasslands.  Locally it is found in Coastal Sage Scrub, Coastal Shrubland and Back Dune/Coastal Prairie communities.   Variety fasciculatum grows primarily below 1200 ft. elevation, while variety foliolosum will sometimes be found as high as 5000 ft. elevation.   Both grow in hot, dry locations with well-drained soils, often on open slopes, mesas and bluffs.   It’s not surprising that California buckwheat is a tough, hardy survivor.

Eriogonum fasciculatum growth habit - Rancho Santa Ana Botanic Garden
Claremont, CA

Like many of our local perennial buckwheats, Eriogonum fasciculatum is a mounded sub-shrub with a woody base and more herbaceous new growth.  Variety fasciculatum, which is typical of coastal sub-shrubs, is more likely to be low-growing – even decumbent (lying on the ground) - particularly along the coast.  Variety foliolosum is more upright and mounded.  Both have numerous, rather thin branches and dense growth.  Mature plants are 3-5 ft tall and wide, but may spread to 6-7+ feet wide in the garden.  Plants have a moderate growth rate and are among the longer-lived native shrubs. 

Leaves, California buckwheat (Eriogonum fasciculatum)

The leaves of Eriogonum fasciculatum give California buckwheat its name.  They are clustered in dense bundles (fascicles) along the stems.  As is common for the genus, California buckwheat’s leaves roll under in the dry months.  In this species, the leaves become very tightly rolled, giving them an almost needle-like appearance.   The leaves are small (3/4 inch or less), dark- to gray-green above, lighter and hairy beneath.  Plants are evergreen except in the severest of droughts.

 

Flowers, California buckwheat: Madrona Marsh Native Plant Gardens,
 Torrance CA

Native buckwheats are amongst the prettiest of flowering plants and California buckwheat is a real prize winner.  The plants are massed with flowers from late spring through mid-summer.  While individual flowers are small (see below), they form dense terminal clusters that can nearly cover the foliage.  California buckwheat’s flowers range from white to pale pink.  The flowers are in parts of six and the stamens (pollen producing organs) extend beyond the perianth, giving flower clusters a fuzzy appearance. 

 

Flowers: California buckwheat (Eriogonum fasciculatum)

California buckwheat is an important pollinator plant.  On a warm summer day, plants are alive with insects ranging in size from butterflies to tiny native bees.  Buckwheats are probably our best all-round summer pollinator plants.  They attract the entire range of pollinator insects: butterflies, European honey bees (honey is delicious!), native bees of all sizes, pollinator flies, beetles and many others.  Plant a native buckwheat if you’re concerned about the health and welfare of our pollinators.

If you’ve only space for one native habitat plant, let it be a buckwheat.  Native buckwheats are long-blooming, supplying thousands of flowers at a time.  The flowers produce high quality nectar and pollen, so they attract both pollen- and nectar-seeking insects.  Many of them are larval (caterpillar) food sources for native butterflies.  For example, California buckwheat provides larval food for Mormon Metalmark, Bernardino Blue and Bramble, Common and Avalon Hairstreak butterflies.  Rabbits and some birds (quails) eat the flowers and foliage. Birds and small creatures take cover under the dense, shady foliage.
 

 

California buckwheat flowers, seeds

As if that’s not enough, the Buckwheats also produce small, tasty seeds.  On a fall day, it’s not uncommon to spot a group of seed-eating birds on/near a garden buckwheat, busily partaking of the feast.  Among those you may encounter are the finches, Dark-eyed juncos and Brown towhees.  Many gardeners let their buckwheats go to seed simply to attract the seed-eaters.  But that’s not the only reason to hold back on deadheading your buckwheats.
 

 

California buckwheat through the seasons. Plant is the shrub just behind
 the right side of the arbor

Buckwheats help us celebrate the cycle of seasons.  Their fresh new growth indicates the height of the growth season; their flowers the end of growth and beginning of the dry season.  And their dried flowers and seeds – with their lovely rust and brown tones - signal the end of the dry season.   The color palette of the buckwheats is an inspiration to artists and garden designers alike.  But the yearly cycle of the buckwheats – unchanging, unhurried and rhythmic – connects us to the earth and our S. California natural heritage.  Priceless!

California buckwheat prefers full sun but will take some afternoon shade.  While it likes a well-drained soil, it can be grown in any local soil from sandy to clay.  If you have a clay soil, consider planting buckwheats on a small berm and be careful not to over-water in summer.  

Eriogonum fasciculatum and most other locally native buckwheats do well in alkali soils, which don’t bother them in the least.  If you use an organic mulch, go lightly.  We recommend starting with a 2” layer at planting time, then letting the mulch degrade naturally, without replenishment.  Once this buckwheat gets going, you won’t need mulch to control the weeds!  For more on mulches see: Understanding Mulches - http://mother-natures-backyard.blogspot.com/2012/07/understanding-mulches_23.html.

Watering California buckwheat requires an understanding of the plant’s survival mechanisms.  This plant has a long taproot, allowing it to access deeper soil water.  It also has shallower, fibrous roots.  It needs good winter/spring water.  In fact, in a dry year like this, we watered our buckwheats deeply about once a month to supplement the rainfall.  The dry season is a bit more challenging.  Some buckwheats, for example Eriogonum parvifolium, are very sensitive and do best with very occasional or no summer water.  California buckwheat – and particularly the cultivars – are more forgiving.   They look good with occasional summer water – perhaps several times in a summer in western Southern California.

Buckwheats are fairly carefree garden plants.  They have few pests and diseases and are generally hardy plants.  Local gardeners cut this species back in late fall to promote plant health.   This cutting back should begin in the first years of life or the plants will become too woody.  Woody old plants should be replaced – with a pledge to prune the replacement properly and regularly.  Cut plants back to 4-6 inches above the woody part of the stem.  That’s about all it takes.

Eriogonum fasciculatum in garden.  It is the shrub with masses of
pale pink blooms behind the bright pink Red buckwheat

California buckwheat is a staple in habitat gardens.  It is often used mid-bed with smaller plants in front of it and can be used as a mid-sized ground cover.  It works well on dry slopes and in areas that are difficult to water.  It complements native Salvias in foliage and flowering.  California buckwheat is planted in rock gardens and can easily be included in gardens featuring water-wise Mediterranean herbs like Rosemary and Lavender.  Once in place, try not to move it – the long taproot makes it difficult to move successfully.

One word of caution: this plant is best planted within its natural range.  It has escaped cultivation and is becoming a weedy non-native  in some areas of Northern California, Oregon, Arizona and Texas.  Be a responsible gardener, particularly if you live near wild areas; plant the species and varieties that are native to your area.

 

Eriogonum fasciculatum 'Dana point'

There are several cultivars that are widely available.  ‘Dana Point’ is a lovely mounded cultivar that does very well in local gardens.  It grows to about 2 1/w ft. tall and spreads to 5+ feet wide.  We have this cultivar in Mother Nature’s Backyard.  It draws raves every year.

Cultivar 'Warriner Lytle' is lower growing – usually less than 2 feet – with dark green leaves and somewhat resembling a prostrate Rosemary.  It makes a good groundcover and would do well on hot slopes.   ‘Theodore Payne’ buckwheat is even shorter (1 ft.) and is also recommended as a ground cover.

Eriogonum fasciculatum 'Theodore Payne'

California buckwheat is used medicinally where ever it grows.  Native Californians and other Native Peoples use it primarily to treat headaches, stomach problems, diarrhea and wounds.  Both the leaves and roots are used, fresh and dried.   For colds, coughs and sore throats and pre-menstrual bloating a mild tea is prepared.  A stronger decoction from roots was traditionally used for diarrhea, stomach troubles and to ‘clean the system’.  A strong tea from the leaves is reported to cure headaches and a decoction from young flowers is used as an eyewash.  A poultice made from dried roots or fresh leaves and flowers was formerly applied to wounds.  For medicinal uses, older established plants are reported to be more efficacious. The small seeds and young shoots are edible.  The leaves were traditionally used to line granaries to keep acorns dry.

In summary, California buckwheat is an extremely useful shrub.  It is excellent for habitat, requires little care and is a great addition to water-wise gardens where ever it grows naturally.

 

 

For a gardening information sheet see: http://www.slideshare.net/cvadheim/gardening-sheet-eriogonum-fasciculatum

For more pictures of this plant see: http://www.slideshare.net/cvadheim/eriogonum-fasciculatum-web-show

 

 

We welcome your comments (below).  You can also send your questions to: mothernaturesbackyard10@gmail.com