San Diego Native Bees

(By K. James Hung)

Hello, world! After many years of not working with San Diego bees (and therefore, having no new posts), I finally have an update! 

A few weeks ago, my colleagues and I published a study that I’ve been thinking about and working on for quite a while after graduating from UC San Diego and moving through my various postdocs. As many of you know, California experienced one of the worst droughts in recorded history a few years back. San Diego was hit especially hard in 2014, right in the middle of my dissertation studies. Although I lost an entire field season (and as a result, got to collaborate with some really wonderful colleagues due to graduating a year later than anticipated :P), I also had the rare opportunity to collect data on native bees both immediately before and after a severe climate event. This opportunity allowed me to evaluate whether climate change, or habitat loss and fragmentation, was the bigger threat to the conservation of native bee biodiversity in San Diego.

The study was published in the open-access journal Insects, so anyone can download a copy and read it for free! Joint Impacts of Drought and Habitat Fragmentation on Native Bee Assemblages in a California Biodiversity Hotspot

I had expected that habitat loss and fragmentation would have had greater impacts on our native bees, but was surprised to find overall, drought had a much greater impact--in fact, nearly 3 times as much. And perhaps worrisomely, bee communities in large, relatively pristine natural reserves generally fared worse than bee communities in fragments of scrub habitat embedded in urban areas, perhaps because (1) reserves harbored more specialized bee species that are more sensitive to any form of disturbance, including drought, and (2) bees living in fragments could access flowers growing in residential gardens and roadsides, which are less impacted by drought due to irrigation. 

(By K. James Hung)

The bee season is winding down in the coastal areas of San Diego. There are a few plant species that are still in bloom, one of them being the laurel sumac (Malosma laurina). If you come across one with fresh blossoms, keep your eyes peeled—you may observe clouds of little mining bees, Perdita rhois, foraging and seeking mates! Please excuse the grainy photos--these bees are small and fast.

A male P. rhois following a female around on laurel sumac as she collects pollen

Perdita rhois is quite small—the smallest I’ve seen is barely over 2 millimeters in length. But what it lacks in size, it makes up for in beauty (as evident in the photo) and prodigious abundance. During their peak flight season, they can be so numerous that each spike of a laurel sumac bush would have 10 or more of these bees crawling around.

Female P. rhois sipping nectar from a laurel sumac flower

The genus Perdita is the largest genus of bees in North America, beating out other mega-diverse genera like Lasioglossum sweat bees, Megachile leafcutter / resin bees, and Andrena mining bees (all of which are more diverse than Perdita on a global scale). They are especially diverse in the American Southwest, where most Perdita species form highly specialized relationships with their host plants. In this sense, P. rhois is rather unusual among Perdita in that it is not a specialist, but rather, seems to accept pollen from many different botanical families. I’ve seen it collect pollen on California buckwheat (Eriogonum fasciculatum), Chamise (Adenostoma fasciculata), as well as toyon (Heteromeles arbutifolia)—all of which are plants that share similar flower color and growth form with laurel sumac, but are in different botanical families.

Another female P. rhois foraging on laurel sumac

Two other cool things about P. rhois: first, this is a species first discovered in San Diego! It was first documented by Cockerell in 1901, foraging on—you guessed it—laurel sumac. And second, one of the most influential bee biologists of our time, Dr. Charles Michener, cites in an interview that this species was one of his early inspirations to study bees.

 Perdita rhois   Cockerell, 1901

Family: Andrenidae

Tribe: Perditini

Active season: Late spring through summer

Range: Southwestern California and Baja California

Floral preferences: Appears to prefer small, white, clustered flowers; not restricted to certain botanical families

(By K. James Hung)

I have written about the beautiful Bombus sonorus before in a previous post, but felt compelled to give an update this year. At the time of the post from April 2014, the Sonoran bumble bee seemed to have all but disappeared from most parts of San Diego County. My colleagues and I had conducted hundreds of hours of pollinator surveys from 2011 through 2013, seeing thousands of bumble bees belonging to the three more common species (B. vosnesenskii, B. melanopygus, and B. californicus) without seeing any Sonoran bumble bees in our study sites. However, this year was different.

The record-breaking drought over the last few years appears to have drastically altered our bumble bee fauna here in San Diego. In our 2015 survey, we found only a small handful of bumble bees in a small fraction of our study sites; a drastic difference from our surveys prior to the drought (map of our survey to come when our study is officially published—now in press at Ecological Entomology). This finding left us quite concerned about our local bumble bee populations. Then, in our surveys this year, the Sonoran bumble bee suddenly started popping up! As of today, we have seen it in 5/6 of our fragment sites and 4/6 of our natural reserve sites, and my colleagues and I have seen it in urban areas all throughout the county.

The Sonoran bumble bees in the above photographs, in order: Foraging on deerweed (Acmispon glaber) in Mission Trails Regional Park, foraging on soap plant (Chlorogalum parviflorum) in MTRP (with a little sweat bee Lasioglossum microlepoides tagging along), foraging on Agapanthus at Faith Community Church, foraging on mallow at the San Diego Zoo, and buzz-pollinating my Sungold tomato plant at UCSD Mesa Gardens.

Bumble bees populations are not easy to study because workers can fly so far from their nests to aggregate at relatively isolated, ephemeral floral blooms (like that lonely orchid tree in your yard), making it difficult to gauge their true colony densities. But such a large shift in the species composition of our bumble bees, in which the Sonoran bumble bee went from being nearly absent to almost completely dominating the bumble bee fauna, is conspicuous and informative.

Here’s one theory for why this drastic shift could have happened. Bumble bee species that establish colonies in the early spring are dependent on there being abundant floral blooms in the early spring. In the recent drought years, those early blooms were much reduced. This meant that our early spring bumble bee species, which were formerly the most common species in our county, had a hard time establishing colonies and thus experienced sharp declines in their populations. The decline of these early spring bumble bees means that there were more nest sites available for Sonoran bumble bees, which establish their colonies a fair bit later in the mid- to late spring, and are less impacted by the reduction in early-spring blooms. This is just a theory; perhaps more research in the future will help us figure out why there was such a big shift in our bumble bees. For now, I’m just enjoying seeing the beautiful Sonoran bumble bee alive and well.

Bombus sonorus   Say, 1837

Family: Apidae

Tribe: Bombini

Active season: Mid-spring through autumn

Range: Southwestern USA and much of Mexico

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

(By K. James Hung)

With the arrival of late spring, squashes of various kinds are beginning to bloom. In Southern California, we have several species of wild squashes in the genus Cucurbita, the same genus that contains our familiar pumpkins, summer squashes, and winter squashes (all different breeds of the same species Cucurbita pepo). And with the blooming of squashes begins the activity of the Eastern cucurbit bee, Peponapis pruinosa, whose name literally means “dusty-looking pumpkin bee.” In much of its range, it is known simply as “squash bee.”

The photograph above shows a male P. pruinosa peeking out of a zucchini blossom in my neighbor’s community garden plot. Squashes have some of the largest pollen grains among bee-pollinated plants—notice that you can see individual grains of pollen on the bee’s face! 

In order to pack and hold on to these large pollen grains, cucurbit bees have adapted very sparse scopae (pollen-collecting hairs on hind legs). The individual coarse hairs of the scopae are visible on the female bee in the photo above. Many thanks to my colleague Jess Gambel for the excellent photography! Jess is studying the effects of climate change on crop pollination by native pollinators using summer squash and Peponapis as her study system. More about her research here.

The map above shows all the known records of P. pruinosa in the global mapper database of www.Discoverlife.org, an online biodiversity encyclopedia / research database. As can be seen, P. pruinosa is extremely widespread! While some have theorized that these bees had spread through the continent by following the relatively recent trafficking of domesticated pumpkins, a group of researchers demonstrated that this species may have colonized the entire USA from their roots in Mexico by following prehistoric range expansions of their preferred squash species (see their study here). Whatever the case may be, the ubiquitous presence of this bee in the USA no doubt contributes to the success of pumpkin and squash growers both commercial and recreational—and as farmers and scientists gain awareness about the importance of native bees, this species has increasingly become the focus of conservation and scientific research. Peponapis pruinosa has an uncanny ability to show up at the right time and place whenever local populations of Cucurbita are blooming—I never cease to be amazed at how these bees are able to find and congregate at seemingly very isolated patches of squashes and pumpkins!

 Peponapis pruinosa  (Say, 1837)

Family: Apidae

Tribe: Eucerini

Active season: Depends on locality; whenever squashes in the genus Cucurbita bloom.

Range: Central America north into southern Canada

Floral preferences: Only accepts pollen from Cucurbita squashes

(By K. James Hung)

Despite the general drought conditions that continue to persist in San Diego’s ecosystems, there were still pockets of time and space this year where rainfall was sufficient to support excellent plant and pollinator communities. Earlier this spring, parts of the Anza-Borrego desert got some of the best rains in the last few years. Because of these rains, we were able to find some pygmy cedar in bloom! Contrary to its name (and appearance), the pygmy cedar is not a cedar—it is a unique plant in the sunflower family (Asteraceae), in a genus of its own: Peucephyllum schottii. And on this remarkable plant, we found some Megachile mellitarsis!

To our knowledge, the bee photographed above represents the first record of this species in San Diego County. Like almost all other members of the family Megachilidae (leafcutter, wool-carder, and mason bees), the female collects pollen not on her legs, but rather on a pollen brush on the underside of her abdomen. One can see that this female is quite productive; she has pollen overflowing even onto the top side of her abdomen!

Little appears known about the natural history of this leafcutter bee, though it can be readily identified by its orange tarsi (“feet”) from which it gets its scientific name (visible in the photo above). While this species is not restricted to foraging on pygmy cedar, available records indicate that it does generally favor plants in the sunflower family. It is interesting to see that this bee has chosen pygmy cedar as its host of choice here, given how rare pygmy cedars are in the area and the fact that the bee occurs in many areas that completely lack pygmy cedars. Perhaps pygmy cedar nectar is especially tasty? We only saw about 15 of them in bloom the whole day, and 100% of the M. mellitarsis we saw were on one of those 15 plants.

Megachile mellitarsis   Cresson, 1878

Family: Megachilidae

Tribe: Megachilini

Active season: Depends on locality; mostly March through June

Range: Northwestern Mexico, western North America

Floral preferences: Appears to favor sunflower family, but may accept other flowers

(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

(By K. James Hung)

Today we feature some photos from my research associate, Jessica Davids, a promising young scientist and excellent photographer-in-training. On a recent bee survey trip to Anza-Borrego State Park, Jessica spent most of her day getting close-up shots of the many plant species in flower and the many insect species we came across. 

The bee pictured above is a female Anthophora hololeuca, one of the smallest in the digger bee genus Anthophora. Whereas many Anthophora species are robust, intensely hairy, and comparable in size to our familiar western honey bee, Anthophora hololeuca (and several fellow members of its subgenus Heliophila) is barely the size of a small house fly. It has a very apt scientific name—“hololeuca” means “all white,” which is very evident in the photo. Even its eyes are very lightly colored.

Anthophora hololeuca, like a quite a few of its relatives in the subgenus Micranthophora of genus Anthophora, is a pollen specialist. In this case, it is the pea genus Psorothamnus, which includes the indigo bush in the above photo (P. schottii), its larger cousin, the smoke tree (P. spinosus), and its smaller cousin, the dye weed (P. emoryi), all of which occur in the Anza-Borrego Desert State Park. When these plants are blooming abundantly, one can often find over a dozen of these little bees zipping about an individual tree, with females collecting pollen (like the one in the first photo), and males chasing females. They are incredibly fast; their white coloration also helps them blend into the grey-white stems of the plant and the white sand on the ground. Thus, despite their high abundance in some areas, they are relatively difficult to closely examine.

Anthophora hololeuca    Cockerell, 1923

Family: Apidae

Tribe: Anthophorini

Active season: March through June

Range: Baja California, northwestern Mexico, Southwestern USA

Floral preferences: Appears to be a specialist on plants in the genus Psorothamnus

(By K. James Hung)

My friends are often surprised when I tell them that there are at least 600 bee species in San Diego and over 20,000 in the world. “How do you tell them apart?” some would ask. “With lots and lots of practice,” is often the answer. While different bee species of the same genus may often be extremely difficult to tell apart from one another, it is usually much more straightforward to tell apart bees belonging to different genera. Of course, this phenomenon has its exceptions, too.

The bee pictured above is a female Tetraloniella davidsoni, a member of the bee tribe Eucerini. As far as I understand, almost all bee genera under the tribe Eucerini are simply referred to as “long-horned bees” without any other common names (except for the genera Peponapis and Xenoglossa, which are referred to as “Squash bees.”). Members of the tribe  are oftentimes extremely difficult to distinguish from one another, leading some authors to lump many groups together into a few genera, and other authors to split groups apart into many more genera (this lumping vs. splitting is a perennial problem in taxonomy research). Long-horned bees are represented by species all over the world, and, like the Tetraloniella pictured above, most are generally robust, hairy bees.

The bee pictured above is the male of Tetraloniella davidsoni. Aha! That’s why tribe Eucerini is nicknamed “long-horned bees!” In the majority of species, males have greatly elongated antennae, presumably to help them locate females. It is interesting to note that I photographed both of the above specimens on checkerbloom mallow (Sidalcea spp.), since other authors have guessed that this species may be a specialist on plants in the sunflower (Asteraceae) family (i.e., they may obtain the majority of their pollen from sunflowers). To my knowledge, Tetraloniella davidsoni falls in the category of “data deficient;” we really don’t know quite enough about the biology this species to say anything definite about it. That’s one of the things that make me excited about my work—filling in the little gaps in human knowledge about our world! :)

 Also I’m going to start adding mini-bio for the bees I introduce, starting with this one. If I get enough free time, I will retroactively add them for ones I posted before, too.

Tetraloniella davidsoni (Cockerell, 1905)

Family: Apidae

Tribe: Eucerini

Active season: March through May

Range: Baja California and Southern California (including the Northern Channel Islands, as I discovered last year—the female photographed above is actually the first documentation of this genus on the islands!)

Floral preferences: Unknown; perhaps specialist on Asteraceae, but evidently likes to hang out in Sidalcea too.

(By K. James Hung)

Spring has arrived in San Diego again! As native bees emerge from their natal nests underground or in wood stems, I, too, shall emerge from my long writing hiatus and begin photographing and writing about bees again. Rain is hitting San DiegoCounty hard as I write, and for the first time since I began my workdocumenting the diversity of bees in the county, we may have a productivespring with lots of flowers in both the mountains and deserts. 

The photo above is a cleptoparasitic bee (i.e., cuckoo bee), Xeromelecta larreae. In our deserts, it can be easily recognized by the reddish to yellow thorax, nearly all black abdomen, very dark wings, and a somewhat lazy, slow flight. Like other cleptoparasitic species, the females do not collect pollen, but find nests of other bee species (their “hosts”) and lay their eggs on the pollen balls therein. Historical records that I could find seem to indicate that this species is primarily active in April; thus my seeing this species at the end of February this year may be caused by the strange climate pattern this year (early rains, and then a period of hot, dry weather). But then again, it seems like there’s no such thing as “strange” or “typical” climate patterns for Southern California anymore these days. 

(By K. James Hung)

Prior to studying bees, I thought that all bees were round, fuzzy, brightly colored creatures. As many readers will know by now, I was definitely mistaken! While bees come in many different colors and forms, the family Apidae (which includes our honey bees and bumble bees) does include a large number of rotund, fuzzy bee species. However, even in this family that includes such familiar members, there are many exceptions.

The photo above is a female small carpenter bee, Ceratina pacifica, collecting pollen from the blossoms of a California thistle. Measuring about 9mm, she is not actually all that small by the standard of bees (and certainly large compared to many of the other small carpenter bee species)--but she is certainly dwarfed by the large carpenter bees in the genus Xylocopa, which can attain the size of large grapes. As one may guess by their similar names, the small carpenter bee and the large carpenter bee are cousins--they are both in the subfamily Xylocopinae.

This photo above is a male Ceratina, probably Ceratina pacifica but also possibly its closest relative, Ceratina punctigena. The males are very hard to tell apart from each other and can only be distinguished with difficulty under a microscope. One can immediately tell that it’s a male, though, by its white “lip” (clypeus). The shape of the white mark kind of reminds me of the Joker from the Batman movie, The Dark Knight--except inverted in color.

Small carpenter bees excavate the centers of woody stems to construct their nests. In the summer and fall, young females would bore into woody stems to hibernate, and the following spring or summer, these females would fully excavate their winter homes into functional nests and begin collecting pollen. We have roughly 20 species of Ceratina in North America, so I will write more about them later.

(By K. James Hung)

About a month ago, I had the pleasure of leading a small team of undergraduates to survey bees during what will hopefully become the annual Bioblitz at the Lake Hodges trails in Escondido/Rancho Bernardo, CA. Even though the weather was very suboptimal for bee activity (it was overcast and even rained at one point), we did find a highly noteworthy bee species: the chimney-bee-cuckoo, Leiopodus singularis.

Huge thanks to botanist and photographer, Dale Hameister, for taking the above photo of this male Leiopodus I found foraging on mustard blossoms. As far as I’m aware, this is the only photo of a properly identified, non-preserved male Leiopodus on the internet. Way to go, Dale! As its species epithet suggests, this is a singular, lonely bee. This is the only member of its genus found in North America; all the other Leiopodus species are in Central and South America. Leiopodus is the only genus in the bee tribe Protepeolini.

The above photo is, to my knowledge, the only photo of a properly identified, non-preserved female Leiopodus on the internet. I took this photo at Mission Trails Regional Park, which has some of the nicest coastal sage scrub ecosystems I’ve ever seen. I highly recommend going on a hike there in the spring!!

(By K. James Hung)

I had the pleasure of helping to lead a pollinator-themed hike at the SD National Wildlife Refuge today alongside Lisa Cox and John Martin. The drought hit the San Diego ecosystem rather hard, and a lot of plants that should be leafy and blooming are dead and dry this year. No doubt some perennial plants were killed by the drought, whereas others did not grow fresh foliage or did not attempt to bloom. Likewise, many annual plants either did not bother to germinate, or were stunted or killed by the dryness (and possibly by the immense heat wave that swept through the region this past week). However!! There were still a few things blooming and we did get to see some pollinators!

The bee photographed above is a male Hylaeus. One could immediately identify this bee to genus based on its sleek black form and pale markings on the face. Males tend to have extensive markings, while females often have just two little strips on the insides of the eyes. This feature earns this bee genus the common name of "yellow masked bees," although a good number of species have white markings rather than yellow (like the handsome fellow photographed here). I'm not going to attempt identifying him to the species level because Hylaeus species around here all look so similar to one another, even under the microscope!

Hylaeus is unique among bees in that the female does not carry pollen using specialized external body parts (such as pollen baskets or pollen brushes). Instead, she swallows pollen grains and regurgitates them back at her nest (which may be tunnels in wood, holes in the soil, or a variety of other cavities they can find). For this reason, it has been really hard to study what plant species serve as the pollen sources for Hylaeus species—as one would need to either dissect foraging females (as my academic elder sibling Professor Erin Wilson at UC Riverside had done during her PhD at UC San Diego), or examine pollen in excavated Hylaeus nests. Hopefully, the Hylaeus species photographed above accepts pollen from the plant this specimen is sitting on (Eriogonum fasciculatum, a.k.a. California buckwheat), because it’s one of the very few plant species blooming in the environment!