A very useful and informative document published by the USDA National Agroforestry Center in 2007.
A very useful and informative document published by the USDA National Agroforestry Center in 2007.
Sweat bees have been weighing on my mind lately. I stumbled across this post, which I thought was well written and informative. I hope you enjoy it as much as I do.
Sweat bees are tiny bees of the family Halictidae. They take their common name from their affinity for human sweat, which they lap off of our naked skin for the salts and electrolytes therein. Sweat bees are small (at least to us) and tend to measure between 3 and 10 millimeters in length. A few species have thick robust bodies, but most are slender and delicate. They tend to be glossy black, but some have exoskeletons which are gorgeous shades of metallic gold, green, purple, or blue.
The majority of sweat bee species nest in the ground (although a few build their homes in dead trees). The social behavior of sweat bees runs the entire gamut of bee conduct: the University of Florida Department of Entomology Website states, “species can be solitary, communal, semi-social, or eusocial.” Sweat bees therefore greatly interest entomologists who are studying the development of eusocial insects—those…
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Whenever I do education outreach, especially with small children, I like to paint a rosy picture of pollination. The bees and the plants help each other; the bee collects food from flowers, and in return they transfer pollen from the male parts of flowers to the female parts of flowers, which results in the production of seeds. We break out the cute fuzzy bee hand puppet and use velcro yellow balls (simulating pollen), which the kids can transfer from felt flower to felt flower.When I talk with older audiences, I might portray a slightly racier scenario. After all, what is pollination other than flower sex mediated by a third party? In the photograph above, look at how tenderly the Halictus hooks its hind leg around the seductively curved stigma of the flower, at the profusion of pollen she has so carefully collected on the hairs of her hind legs to carry between flowers. Despite the more adult tack I use, I still tend to emphasize that this is a mutualistic engagement; the flower has evolved nectar and enticing patterns to seduce the bees, and in return the bees transfer pollen between plants. A nice example of this are something called nectar guides, or patterns in the UV spectrum (visible to bees but not to us) that guide bees towards the nectar reward in the flower.
And so the flowers grow. And so we get fruits and nuts and seeds. And so this green planet fluorishes.
As idyllic and parabolic as this picture may be, it brushes over a Machiavellian but more accurate version of how pollination (and evolution, for that matter) really works. In a way, I feel guilty teaching this airbrushed version of pollination because in some ways it may misrepresent how evolution and symbiotic relationships work in real life: as an escalating arms race.
In this darker world, flowers evolve to attract pollinators in order to increase reproductive fitness. In parallel, bees evolve to collect sugar rich nectar and protein rich pollen from flowers. As a byproduct, flowers feed bees and bees pollinate flowers, but this is not the purpose of the plant or bee, merely a byproduct of their concurrent actions.
And thus we enter the dark underbelly of the world of pollination, full of cheats and robbers and generally bad behavior. After all, it takes energy on the plant’s part to produce nectar and nutritious pollen, and pollen that is transfered by bees between plants is pollen that the bee cannot eat. If a bee can find a way to eat without pollinating, or a plant can find a way to be pollinated without feeding the bee, this may give them an edge over their competitors. One basic example of this that we see are bees that fastidiously clean all excess pollen off themselves before leaving a flower. Especially for a small bee, pollen can be quite heavy and make it more difficult to fly. By cleaning itself before takeoff, a bee can travel between flowers more easily but does not pollinate the next plant it visits.
Let’s take a look at the aspects of pollination I leave out of my classroom visits: the sex, the drugs, and the violence.
Sex and Drugs: The Cheating Orchid
The Bee Orchid preys on the sexual urges of male bees and wasps, luring them with drugs called pheromone mimics into a senseless orgy of failed mating. The flower copies in its shape, color, and texture a female bee or wasp. Furthermore, it entices males by releasing an intoxicating perfume: the smell of a female who is ready to mate. Hapless males converge on the flower and fight each other for the chance to attempt to mate. In the process, pollen packets called pollenia attach to the male. The next time it tries to mate with an ersatz bee, the pollenia make contact with the female part of the flower. In this scenario, the cheating orchid reaps all the benefits of pollination while the males get nothing but frustration and lost mating opportunities. For a great video of bee orchids in action (not to mention a rockin’ synthesizer soundtrack), check out this neat excerpt from Wild Orchids of Israel, filmed by Doron Hirschberg:
And Now for some Violence: Big Bad Carpenter Bees
Bees are no strangers to cheating at the pollination game, either. In my Xylocopa post, maybe you noticed that the gargantuan carpenter bees, rather than venturing into the trumpet-shaped structure of the sage flower, clutched onto the outside of the flower. Perhaps you even noticed a dark, drinking straw structure unfurled from the head of the bee and piercing into the flower through the side, rather than the front entrance.
The sage flower is designed for a pollinator to enter the main opening of the flower in order to reach the nectar. In the constricted petal tube, the bee must crawl past the anthers (pollen bearing structures) to reach the nectar, thus getting covered in pollen. This carpenter bee has other plans, however.
Using its heavily armored mandibles (used to chew through rotting wood to build nests), the carpenter bee rips a hole in the base of the petals, next to the nectar reward. It then sticks its proboscis in through the hole it has ripped, like a kid in a Tropicana orange juice commercial, and drinks the nectar without ever touching the anthers of the flower. The defenseless flower, once ripped open, is now vulnerable to other smaller bees that can use the hole made by the carpenter bee to access nectar directly. This process is called nectar robbing, because the flower is robbed of its nectar but reaps no pollination reward.
So the next time you go out to enjoy a pleasant Spring day, as you watch the industrious bees trundle from flower to flower, take a moment to reflect on the dark designs of both flower and bee. Although salacious and exploitative, I don’t like to think of this interplay in a negative light. To me, the complexity of coevolution makes this relationship more interesting, more beautiful, more strange than the boring stories we tell our children. This intricate biological world we live in operates by its own set of rules separate from Western human morality, and we have much more to gain by learning and appreciating these rules rather than placing value judgments on them.
I’ve been distractingly busy with work this week, so no in-depth post today. Just some filler photos of a bee I encountered in Tahoe National Forest. As you can see from the orange on her hind legs, she is busy collecting pollen to feed her young.
I’m not sure what type of bee this is, because I didn’t collect her for identification (after all, she’s working so hard to feed her family). Based on the fuzzy thorax and the style of striping on the abdomen, I think it might be in the genus Andrena. Andrena is a fairly diverse group of mining bees, or bees that build their nests underground. Unlike honeybees, bumble bees, and some sweat bees, all members of this genus are solitary. Each female excavates and provisions her own nest; there is no hive or queen. Or a more fanciful way to look at it would be to think of each female is the queen of her own solitary kingdom.
See you next week!
When the weather complies, I like to take a slightly longer walk from my office to my research site. The advantage of this route is that it takes me past a nice planting of Autumn Sage (Salvia gregii). I was a botanist before I started studying bees. But while I certainly enjoy a nice Lamiaceae bloom, that’s not the only reason to take the circuitous path.
In a previous blog post, I shared with you some photos of the gorgeous Patagonian Bombus dahlbomii, the largest bumble bee in the world. If you live in the United States like I do, you don’t have to travel all the way to the Southern Hemisphere to spot a giant of your own.
This beauteous behemoth is a carpenter bee (genus Xylocopa). There are about 500 species of carpenter bee worldwide. If you live in California’s Central Valley, there are 2 species living in your backyard alone. With some of the most prodigious mandibles (entomologist speak for “jaws”) in the bee world, carpenter bees derive their name from the female’s habit of constructing elaborate nests in rotting wood, thus flouting human stereotypes of gendered careers.
The lovely Autumn sage attracts more than one kind of visitor, however. After all, who could resist that tasty nectar? In addition to the enormous carpenter bee, much smaller sweat bees also frequent this popular drinking spot. For size comparison:
As I mentioned in my first post, there are over 20,000 species of bees. These creatures vary greatly in all aspects, including size. This sweat bee isn’t even the smallest bee I have encountered; some could barely see eye-to-eye with an ant. The next time you are enjoying a garden on a warm, sunny day, take some time to watch a few flowers up close and observe who visits. You might be surprised by how many types of bees you encounter.