#sdnative

[irieotter]

#DayTrip #SDMountains🗻#SDNative #BeautifulDay #Bae💞 #LakeCuymaca #JulianPie #Cememtary #StayHumble #StayWoke #StayClassySanDiego✌🌴🎄❄ (at Julian, California)

[sdnativebees]

Bombus melanopygus: black-tailed bumble bee

(By K. James Hung)

When I first started my field research in San Diego in 2011, bumble bees were a conspicuous and consistent element of the pollinator fauna almost everywhere I looked—I would see over 100 of them during a typical week in the field. The following year, 2012, was not too different. However, bumble bees seemed to have taken a sharp decline starting with the drought in 2013; and this year I have seen fewer than 10 bumble bees despite having spent over 100 hours in coastal San Diego looking at bees and flowers. Thus, I was overjoyed this past weekend when my team and I went to the Combs Peak area of Anza-Borrego State Park, where we saw dozens of black-tailed bumble bees, Bombus melanopygus happily foraging on the blooming plants! As with last time, many thanks to Jessica “Bastian” Davids (who has now become the bee team’s dedicated photographer) for the pictures!

Two black-tailed bumble bee workers, perhaps sisters, foraging together on California thistle (Cirsium occidentale).

Bombus melanopygus is one of the earliest-emerging bumble bees in Southern California, and can be seen foraging on early-blooming shrubs like manzanitas (Arctostaphylos).  It is somewhat smaller than our other four bumble bee species, and unlike its primarily ground-nesting cousins, it sometimes nests aboveground in tree cavities or bird boxes. This is a species with a medium-length tongue as far as bumble bees are concerned, giving it access to both shallow and deep flowers (though it is not particularly excellent at handling flowers on either extreme), making it potentially more adaptable than its long-tongued cousins like the Sonoran bumble bee introduced earlier. All of the bumble bees I have seen in my study sites near the coast have been B. melanopygus this year. 

A male B. melanopygus sipping nectar from thick-leafed yerba santa (Eriodictyon crassifolium).

Since bumble bees start new colonies from scratch each year, blooming flowers are a hugely important resource for them in the winter and early spring when new queens emerge from hibernation and start foraging. This is potentially why bumble bees have declined so visibly in coastal San Diego, since the last three years of drought have really limited the abundance of wildflower blooms between January and March. Unlike some desert bees that seem to be able to remain dormant for several years as larvae to escape drought, it appears that bumble bee queens have no option other than to start fresh colonies each year even in the face of unfavorable climate. Thus, consecutive years of drought may be especially detrimental for bumble bees.

Bombus melanopygus    Nylander, 1848

Family: Apidae

Tribe: Bombini

Active season: March through August

Range: Northwestern Mexico, western North America excluding deserts and very high mountains

Floral preferences: Eclectic, will forage from a wide array of both native and non-native plants

Nesting biology: Colonies are usually underground but may be in above-ground cavities. A single queen founds the colony at the beginning of each active season; new queens leave and colonies dissolve at the end of each summer.