Now that late summer is upon us, bumblebee nests are full of worker bees. These bumble-workers often stay out in the field at night, sleeping in flowers. I found this bee in a dewy Yellow Cosmos bloom. She was completely still, paralyzed by the cool morning temperatures.
Like mammals and birds, bumblebees are endothermic, meaning that they warm themselves from internal heat sources. Bumblebees do this by shivering their flight muscles as they wake in the morning. Until they reach running temperature, they are sluggish and can barely move a leg, let alone fly.
In the arctic, some bumblebees use their bodies’ heat to incubate eggs and young bees, just like a mother bird. Without a boost of maternal muscle-heat, the bees would not have enough time to complete their life cycle during the short arctic summer. This endothermic physiology explains why bumblebees, especially northern bumblebees, are furry: like birds (feathers) and mammals (hair), they have a layer of insulation to retain hard-won heat.
Our local bees’ nightly cold stupor saves energy. But immobility is is a dangerous habit, especially for footloose bees who like to sleep outside of the nest in exposed flowers. Yesterday, I watched a European hornet patrolling the profuse blossoms on a clematis vine. Every time it came across a bee or fly, the hornet lunged, trying to grab the victim.
Look sharp, little bee. An evil Puck is after your life.
I’ve been using some salvaged wood to make repairs to the goat barn. One of the pieces seemed unusually light. I flipped it over and found a perfectly round hole on one side: the entranceway of a female Eastern carpenter bee, Xylocopa virginica.
The bee that left this hole used her mandibles to gnaw into the wood, then she slowly tunneled through the timber. I’ve seen these bees at work on the rafters of several of the small barns that we’ve built for animals and hay. On a quiet day in early summer you can hear the crunching of chitin on wood as the bees make their slow progress. Below the holes, small piles of sawdust accumulate.
I’ve seen many entrance holes, but never had the opportunity to see the extent of the tunnels inside. So I made a series of longitudinal cuts in my wood scrap, a 4×4 dissection of sorts. Inside, I found the tunnels extended about a foot away from the hole. One or two tunnels branched. This is an impressive hidden network, like a subway with just one exit. No wonder the piece of wood was so light.
The bees make these tunnels for their young. The female makes a ball of pollen and nectar, then lays an egg. All this is sealed into the tunnel with a slug of compressed sawdust. Once the passage is sealed, the mother leaves her offspring to their fates. These futures sometimes involve woodpecker beaks. The drilling of these hungry birds will finish what the bees started. The two species, bee and bird, are an anti-carpentry team. But I also think of these animals as supreme carpenters: they’ve been making homes from wood for millions of years and they spend their lives happily sprinkled with the sawdust of their labor. So they are both über- and anti-carpenters.
Away from wood, the bees do good work as pollinators. They are eager visitors to many species of flowering plant. Some farmers even erect pieces of wood to attract them into their orchards. I’m OK with a few at our place, but a year ago we had an invasion of battalions of barn-destroyers. So I relived my glory days of college squash-playing, dispatching them with a killer backhand from a dustpan. I felt bad, but not as bad as I would have had the barn needed rebuilding. These days we just have a few carpenter bees buzzing around and I leave them alone.
Tennessee’s only native cactus, the prickly pear (Opuntia humifusa) is coming into flower. The flowers stand on top of the fleshy green stems like torches on monuments — an apt comparison in both shape and brilliance of color. The gorgeous intensity of orange and yellow in these flowers is hard to convey. Wow. I feel my wax wings start to melt.
This cactus grows in places that are too hot and dry for most other plants: rocky outcrops, dunes, gravel, and thin rocky soil. I found this cluster of plants on the lichen-encrusted sandstone outcrop behind the Fulford Hall parking lot in Sewanee. There are dozens of cactus plants there, each one bearing several flowers. I’ve never seen such profusion. Perhaps the long warm spring has suited them.
Bumblebees love the flowers. Such is the strength of their desire that several were fighting their way down between the petals of unopened flowers. Later this summer I’ll check the patch again. The pulp of the fat red fruits is edible, although the spines urge caution in this gastronomic quest.
The last hummingbirds of the season are feeding in the jewelweed patch behind Stirling’s Coffee House.
Jewelweed flowers offer nectar to the hummingbirds from a nectar spur at the end of a cone-shaped flower. The hummingbirds have to insert their beaks all the way in to reach the nectar and in doing so they receive a dab of pollen on their foreheads. Many of the hummingbirds in the patch have heads that are completely coated in pollen.
Jewelweed, Impatiens capensis, with nectar spur visible on the far right
The last thing a hummingbird sees before it sinks its beak into the flower. The pollen dusters are at the top of the flower.
Not all spurs are the same shape. Some are curled, others are straight. It turns out the the more curvy spurs result in better pollen transfer to the hummingbirds, probably because the birds have to reach down further to get the nectar.
Compare this piglet-tailed spur to the one above.
The degree of curvature is heritable, so this is a feature that can evolve through natural selection. Why, then, don’t all flowers have the same degree of curl? No-one knows, but the diversity of pollinators that visit jewelweed may favor a diverse set of nectar spur designs.
Bumblebee visiting the same jewelweed patch.
Jewelweed is also called-touch-me-not: a gentle pinch to the bottom of the seed capsule will cause the seeds to explode outwards, shooting several feet away. Gram for gram, the energy stored in these seed pods exceeds that of steel in springs.
Waiting to explode...
As an extra bonus today, the jewelweed patch also hosted a beautiful red phase screech owl. The scolding wrens gave away its location in the shrubs.
Goldenrods (Solidago sp.) are in full bloom, giving insects a welcome bonanza of pollen.
A bumblebee packs pollen into "baskets" on its hind legs. The baskets are made from long hairs.
Paper wasps (genus Polistes) also love the flowers. Some studies of goldenrod ecology suggest that these wasps may be the main pollinators of goldenrod. These wasps are normally very flighty, but on goldenrod they seem to settle down to the serious business of investigating every floret on the flower stalk.
Our Seminole squash vines have dozens of flowers, each of which is stuffed full of bumblebees (or, as Darwin called them, humble bees).
Seminole squash flower
The bees cram their heads under the central column (the pistil that gathers pollen from incoming bees), lapping at the nectar that oozes below. Occasionally a bee will break away and fly to another flower, but mostly they keep their heads buried in the flower, moving only to push themselves deeper into the nectar.
Seminole squash flower with bumblebees
The photographs above are of female flowers. Interestingly, the male flowers are a little smaller and, although they attract bumblebees, they don’t seem to elicit from the bees the same adoration and abundance.
Male Seminole squash flower
According to RAFT (Renewing America’s Food Traditions), this variety of squash is one of America’s ten most endangered native foods. This breed of squash was originally cultivated by Native Americans in and around the Everglades by girdling trees and letting the vines grow up the dead limbs. This gave the plant its other common name, “hanging pumpkin,” for the arboreal fruits. We’ve grown this variety for two years now. Its vines and leaves are enormous and they tend to smother all other plants in their path as they grow outward. They are phenomenally productive and seem to have no problems with disease. And, evidently, the bumblebees love them.
The Lake Cheston spillway is now choked with meadow beauty, increasing tenfold the number of blooms.
So many bumblebees are in attendance that the air hums with the sound of their work.