very busy bees

The number of bees in the backyard has quadrupled (or more) since New England Asters and Yellow Oxeye Daisy have begun blooming. On warm days the bumblebees and honeybees swarm over the flowers, probing quickly and moving on.

But on closer inspection, I saw a number of smaller bees that were sharing the pollen and nectar resources as well.

The Common Eastern Bumblebee dwarfs the tiny metallic Green Sweat Bee, but there are so many flowers blooming now, there is little interference from competitors.

With the help of my trusty macro lens, I tried to zoom in on what these tiny bees were doing.

Miniscule Small Carpenter Bees were the perfect size to get their head and tongue into the tiny crevices in the disc flowers of Rudbeckia flowers.

Small Carpenter Bees, like their larger cousins, are good at chewing their way into plant stems, constructing nesting chambers in the central pith for their larvae.

A Dark Sweat Bee and an unidentified, slightly out of focus bee with very long antennae and a very fuzzy thorax shared one flower head.

Sweat Bees were supposedly named for their attraction to moist, salty sweat on exposed skin of humans.  Species in this very large bee family are typically small, often less than an inch in length, may be eusocial (with a queen and worker castes), and are one of the most important pollinators of commercial crops, like squash, legumes, sunflowers, watermelons, apples, cranberries, blueberries, strawberries, tomatoes and peppers, as well as native flora appearing in all seasons in in woodlands and fields.

I followed one of the metallic Green Sweat Bees (an Agopostemon species) around the patch of New England Aster as it inserted its incredibly long tongue deep into the aster flowers.  Males have a yellow and black striped abdomen (mimicking a wasp?), while the female is a glossy green all over.

They are a challenge to photograph because their head is usually buried in the flower, and they pause only very briefly on a flower, dipping deeply into it, before moving on.

It looks like this sweat bee has a leg coming out of its mouth, but that is its long, flexible tongue being pulled out of one floret.  When it is not feeding, the tongue folds down on its ventral surface. Notice that this male’s body and legs are relatively pollen free, unlike the female in the next shots.

I don’t know if this female Green Sweat Bee is the same species as the male in the previous photo, but this shows how different the two sexes are in coloration.  And unlike the case of sexual dimorphism in bird or mammal species, the female Green Sweat Bee is hardly drab or well camouflaged.

Her hind legs and head are covered with pollen, unlike the male in the photo above.  She buried her head deeply into each flower as she foraged, transferring pollen as she went.

It’s possible someone that lives near me has some honeybee hives, because their numbers are way up this year. But there are still far fewer of them present on these early fall blooms than the Eastern Bumblebees and the small Sweat and Carpenter bees that swarm over these flowers.

Ornithophily

Word of the day:  Ornithophily — or obligate pollination by birds, and typically by hummingbirds.  Last summer, I wrote about the coevolutionary “perfect fit” of Ruby-throated Hummingbirds and Cardinal flowers.

As the hummingbird dips its beak into the long flower tube, the top of its head picks up pollen from the flower’s anthers.  The male (anther) parts of the flower are first to project from a new flower.  A day or two later, the anthers fold down and the female (stigma) projects from the flower tube to receive pollen from younger flowers.  In this way, the plant ensures that it gets cross-pollinated.  See Back Yard Biology, Aug 17, 2013/

Plants that depend on birds for pollination typically provide much higher volumes with higher sugar content of the nectar than insect-pollinated flowers. In contrast, insect-pollinated flowers tend to be heavily scented but have meager nectar with low sugar content.  So it’s no wonder so many insects find ways to enjoy the riches of bird-pollinated flowers without performing the vital pollination service.

A large clump of Scarlet or Crimson Beebalm in my garden, with its ornithophilous flowers, awaits its pollinators — the Ruby-throated Hummingbirds.

Honeybees (but there was only one in the garden) land on the lower part of the flower and climb into the long tube to reach the nectaries at the base of the corolla.  Their slender bodies fit perfectly into the floral tube, completely avoiding the anthers and stigma projecting from the flower.

Side view of the same approach by the honeybee as it walks into the flower tube.  The Y-tipped stigma and lobe-shaped anthers are clearly far away from the dorsal surface of the bee.

This bee had a good long drink of nectar in this flower before moving on.

Even the bumblebee tried getting some of that rich sucrose each flower in the cluster provides.  However, the bumblebee’s chunkier body didn’t permit it to actually crawl into the flower.  Some Bumblebee species have a long hairy tongue that helps them reach deep into the flower.  I don’t know if this is one of those species.

I think Bumblebees might also have a different strategy to harvest nectar from flowers they are too large to crawl into.  Its body weight is enough to pull the flower down and allow nectar to flow down the floral tube toward the opening where the bee could lap it up.

Bumblebees might be large enough to contact the anthers and/or stigma as they try to crawl into the flower. At least that’s what it looks like in this photo.  

Another nectar thief, the Clearwing Hummingbird Moth also enjoys the rich nectar of Scarlet Beebalm without coming close to contacting the flower’s reproductive parts.  Photo by Kate St. John.

Ornithophily has its risks.  If birds don’t find the flowers or weather throws off the timing of the arrival of the birds and flower blooms, the plants risk not getting pollinated at all.  But in the case of the beebalm flowers, bumblebees might be able to make up for the lack of bird pollinators by transferring some pollen.  Why else would they call it bee-balm, and not bird-balm?

In search of pollinators

The plight of the honeybees got top billing in the Minneapolis paper today, with a feature article on our endangered food supply that is so dependent on bee pollinators, honeybees in particular.

Bees of all sorts love the nectar of the late summer blooming sedums. I rarely see such a concentration of honeybees on a plant these days.

You might have known about the California almond crop dependency on honeybee pollinators (in fact, almonds are 100% bee pollinated), but broccoli, various fruits including cherries and blueberries, cucumbers, and melons (among 100+ foods we eat regularly) are also heavily dependent on bees for pollination and fruit set.  Honeybees are in trouble for a variety of reasons, many of which have to do with the impact of agro-chemicals on insects of all sorts.

Butterflies are less important for pollination of agricultural crops, but vital to the pollination of certain wildflower species. Butterfly weed (Asclepias tuberosa) probably got its name originally as a result of its attractiveness to a variety of butterflies (as well as bees).  But where are all the butterflies these days?

Their bright orange advertisement should bring pollinators running (or flying) to it, but ants were the only insects on this plant sitting in the middle of a 10 acre prairie.

Ruby-throated Hummingbirds enjoy the nectar that butterfly weed flowers have to offer, but they don’t move pollen from plant to plant. I never saw butterflies, and rarely any bees, on this plant in my garden, but they did manage to make a few seed pods.

Our local butterfly populations seem sparse compared to what they were a few years ago, whether a result of harsh winters, late springs, drought in areas through which they migrate, habitat destruction in their overwintering areas, or too many chemicals in the environment.

In a 3 hour walk around Tamarack nature center this morning, I saw this one Swallowtail butterfly (nectaring on Hoary Alyssum), one Red Admiral, and one Wood Satyr. Three butterflies in three hours — not a very impressive count.

In China, they pollinate fruit crops by hand — I hope that isn’t what we will have to resort to in the future.

Nectar feast

Late-blooming Sedum species provide a bounty of nectar for overwintering and migratory bees and butterflies.

Bumblebees, honeybees, and tiny green sweat bees ignored each other as they crawled over the open flower heads of this Autumn Joy Sedum (a member of the stonecrop family).

Flowers produce only tiny amounts of nectar, but there are so many of them that a clump can support dozens of foraging insects.

Empty pollen baskets indicate that the bees are foraging just on the nectar. I was surprised to see so many honeybees on this plant.

Bumblebees of different sizes — might be the same species but different sizes based on their caste (e.g., worker vs queen).  There were some tiny bumblebees less than 1/4 the size of the big one in this photo.

In walking around the neighborhood this morning, I noted that more than half the landscaping includes this species.   What a feast for the bees!

Buzzz….

I keep wondering where the bees are, and finally they are starting to show up — just a few bumble bees, as well as honeybees.

Bumblebee coming in for a pollen snack from Compass Plant flowers

Bumblebee working on purple prairie clover.  That’s quite a load of orange sticky goo in its pollen baskets.

Bees seem to bury their heads in a flower, and you rarely get a glimpse of their long tongue that laps up the nectar.

The tongue is that brown triangular shape between the bees legs. It is actually encased in a sheath, so that only the tip is immersed in the nectar at the bottom of the flower structure.

Since bumblebees (and other bees, ants, and bats) are nectar dippers, the tips of their tongues are specialized mops with hairy fringes that can soak up a syrup of at least 52% sugar.

The tip of the bumblebee tongue that protrudes from the sheath is formed of fine filaments that collect and hold droplets of sugar-rich fluid.  The saturated tip of the tongue can be withdrawn into the mouth in between flower visits. (Photo from bumblebee.org)

In contrast, suction sippers like butterflies, moths, and hummingbirds prefer a less viscous nectar of around 30%, in order for the mixture to flow well up the capillary tube “tongues” they insert into flowers.  You can read more about this research here.

Milkweed flowers provide just the right mix of sugary nectar, and are usually loaded with bees at this time of the year.  However, bee visitors are still rare this summer.

The bees still have a month or two to provision their nests and young before the weather turns cold again.  But does a short summer mean fewer bees next year?

Pollen eaters

Much has been written about the benefits of the intimate relationships between plants and their pollinators.  Plants provide the nectar (sugar) reward for the services of an animal that moves pollen from one flower to another.  Nectar isn’t the only reward, however; animals collect that pollen for their own uses.

You don’t really need that much pollen to fertilize the neighboring flowers.  This little syrphid fly will ingest the pollen as it cleans itself.

Unlike the solitary syrphid flies (hoverflies) that feed directly on flower pollen, bees collect pollen to take back to their hive to feed their larvae and for storage for future consumption.

The rear pair of legs have specialized hairs that form a “pollen basket”.  Full baskets make the bee look like it is wearing pantaloons.  A famous bee researcher (Karl vonFrisch) once measured the time it took to fill a honey bee’s pollen basket — just three minutes in some cases.

A small bee on a big anther must fill its baskets in just one stop.

So many flowers, so much pollen, it sounds like an easy way to gather food.  But nothing in nature is that easy.

Grains of pollen from many plant species differ in size and structure, but have one thing in common — they are really tough to break open.  From Wikipedia:  http://en.wikipedia.org/wiki/File:Misc_pollen.jpg

The pollen coat is so tough that it can resist decay for millions of years in bog and sediment deposits.  It cannot be broken down by freezing, grinding, or boiling in acid. So how does a mere animal with a relatively soft, chitinous exoskeleton manage to break into the rich interior of a pollen grain?

By tricking the pollen grain into opening its germination pore, just as it would if it landed on the sticky surface of a flower stigma.

Pollen grains of horse chesnut (buckeye) split open around the germination pore when bathed in a sugar solution.  

Immersing pollen in a sugar solution in an insect’s gut is all that is needed to initiate the germination process, which normally would result in the growth of a tube from where the pollen grain landed on the flower stigma down into the ovary.  In another chamber of the insect’s (or bat’s or bird’s) digestive tract, then, digestive enzymes can attack the interior of the pollen grain through the germination pore, and release the carbohydrate, lipid, and protein stored there.  It turns out this pseudo-germination trick is used by most pollen eaters.  (Read more about this here.)

But Heliconius butterflies exhibit a different strategy.

Heliconius butterflies sipping nectar, taken at the Insectarium in New Orleans, LA.

Butterfly mouth parts are adapted for sucking nectar not ingesting pollen. To get around this potential disadvantage, Heliconius butterflies collect pollen on the tip of their proboscis, secrete some of the nectar they have sipped onto the dry pollen mass, and then agitate the mass with their proboscis for many minutes, while the germination process begins.  The volume of nectar that is eventually re-ingested then contains amino acids and fatty acids that the butterflies need for egg production. (Read more about this here.)

Perhaps other butterfly species do this as well.  If a curious young grad student hadn’t noticed that Heliconius butterflies sometimes spent 10 minutes at a flower instead of their normal 3 seconds, this amazing behavior might have gone unreported.