A Reassuring Hum

by Sue Avery

One of my favorite sounds of summer is the rhythmic hum of bees as they move from flower to flower. I love to watch these industrious insects as they dance on the pink florets of Joe Pye weed or dive into the hairy throat of penstemon. I marvel at the variety of buzzing visitors on blooming goldenrod and the constant taking off and landing on the face of a sunflower. The bees come in all stripes and sizes – some slender with heart-shaped faces, some with yellow or masked faces, some hairier than others, some tiny or huge by comparison. There are even some that are a metallic green.

Bees and flowers have evolved closely for about 130 million years and it is a matter of “give and take” when a bee visits a flower. The shape and color of petals, alluring scents and sweet nectar attract the bees, which in turn take sustenance and a supply of protein-rich pollen for their nests. Put simply, where there is no pollen there are no bees. Bees are prime pollinators because their offspring are raised solely on a diet of nectar and pollen. The female bee in particular transfers pollen at a high rate as she repeatedly visits many flowers in order to provision her nest. If there were no bees, we would have far fewer colorful flowers and a restricted diet. A third of the food that we eat comes from pollinated plants.

Flowers have evolved brightly-colored petals as advertisements amongst leafy green and as storage for rewarding reserves of nectar. Petals reflect ultraviolet light and often have nectar guides. The striations of contrasting color on wild geranium petals and spots on horsemint lead the way into the depths of the flower where the nectaries lie. Some flowers, such as those in the mint and pea families, have flattened lip-shaped petals, which act as landing pads for flying visitors. A bee perceives light at the UV end of the spectrum, it recognizes symmetry and patterns of color, and by using the sun as a compass it learns to navigate its way to and from a flower and the nest. Bees smell with their antennae and they obtain information about flowers from scents that waft from glands in petals or by perceiving pheromones left by previous visitors. Male bees collect floral oils from petals to attract a mate.

The length and shape of a bee’s tongue determines which flowers they will visit. Long-tongued bees visit deep, tubular-shaped flowers, such as penstemon. Bumblebees, whose tongues measure up to 18mm in length, can easily access the nectar of wild columbine that is stored in the tips of petals shaped as narrow tubular spurs. Smaller bees with short tongues visit flowers with a more open access, such as those in the daisy family, which are visited by a whole host of pollinating insects and many different kinds of bee. Open, bowl-shaped flowers, such as Virginia rose, produce copious amounts of pollen but have relatively lower amounts of nectar than tubular flowers. Pollination takes place more easily in these flowers and so there is not such a need to entice bees with a sugary reward.

A distinguishing feature of bees, and one that makes them such efficient pollinators, is their hirsuteness. Furthermore the hairs on a bee’s body have branched tips, which easily trap pollen. When a bee forages it is more often than not carrying pollen from another flower. On dancing over a daisy, or when disappearing into a floral tube to find nectar, bees transfer pollen to strategically-placed female parts of the flower. The legs of the bee have a comb for brushing off pollen, which is moistened and pressed into a pollen basket or packed between stiff bristles on the hind leg or abdomen. Only the female bee actively collects pollen, which she manipulates midflight with much dexterity. After all, she is too busy to pause too long on the face of a flower. It’s on to the next one for more nectar and pollen before returning to her nest. Some bee species are selective on which plants they visit to collect pollen and their life cycle is closely tied to these plants. Hence, they are particularly vulnerable to changes in their habitat. Bumblebee queens will overwinter and build their nest close to spring ephemerals and many of these early-blooming plants rely solely on these bees for pollination. There is also variance amongst species on foraging distance. Larger bees might fly a mile or so from their nest, smaller ones no more than 200 yards.

It is easy to see the huge diversity of bees just by looking closely at their habits as they visit the native plant gardens at Seatuck. There are estimated to be 447 species of bees in New York State, grouped into six families. Most of them are solitary nesters, which means they do not form a social colony. However, the Apidae includes some bees well known for making colonies, such as honeybees (introduced from Europe) and bumblebees. Carpenter bees, who are also in this group make solitary nests in wood. Some members of this family, bumblebees in particular, are pollinators of plants that require what is known as buzz pollination. Blueberry flowers have tubular anthers on which pollen is firmly attached and only shaken loose when a visiting bee rapidly vibrates its flight muscles in close proximity to the flower. Bumblebees have been imported to Australia and parts of Asia with the prime purpose of pollinating tomato crops. Otherwise the tomatoes are laboriously pollinated by human hand. To the musically inclined, the frequency of a buzz pollinator’s hum is of the middle C musical note! The Halictidae, known as sweat bees, are a family that shows a wide range of nesting behavior, from solitary to social. These are tiny bees, some as small as 4mm long, and many have a shiny metallic sheen in colors of green, copper, gold or black. I often see strickingly beautiful green sweat bees on the yellow flowers of prickly pear cactus or evening primrose.

The mining bees, Andrenidae, excavate soil to build underground nests. These are solitary bees but after several years in a suitable habitat a colony forms and the females might share a nest entrance. Look for their activity in early spring in the terrace garden at Scully, where year after year quite a colony forms in bare patches of the lawn. Mining bees collect pollen from early blooming plants such as maple, willows and violets. Colletidae are the polyester bees, so called because they line their nests with a watertight substance, which they apply with their paintbrush-shaped tongues. Then there is the Megachilidae family, which includes the leafcutter bees and mason bees. These bees find hollow plant stems or crevices and adapt them for their solitary nests. Leafcutter bees will partition and line each brood cell with pieces of cut leaf. If you find leaf margins with perfectly rounded cuts you are most probably looking at the handiwork of a leafcutter bee. The mason bees mix mud and other malleable material with saliva to partition and seal each brood cell. Perhaps we will get to see some of the tubes, provided within the Seatuck insect hotel, daubed in this way. Lastly, a very few species belong to the Melittidae family, which collect and use floral oils in their nests.

Unfortunately, there has been a dramatic decline in some bee species in recent decades. Disease, invasive plants and the use of pesticides are considered to be contributing factors. European honeybees are also thought to be responsible for introducing disease and out-competing native bees for pollen and nectar. Scientists have found that bumblebees exposed to neonicotinoid pesticide have impaired brain function leading to difficulty with navigation during foraging. Climate change, degradation of habitat and methods of agriculture have reduced the availability of the very plants that bees have evolved with and rely on for survival.

Just by planting flowers and gardening to create a favorable habitat for bees we can go a long way to reverse this decline. We can start by reducing areas of lawn and instead grow flowers of all shapes and colors that bloom in succession from early spring through fall. We can grow native, open-pollinated plants. Cultivars and hybrids are sometimes sterile with no pollen and may have an altered petal structure. We can group the same plant species together so that bees do not have to travel so far to forage. We can allow for some rough areas on the lawn or edges of the garden: dandelions, clover and other weeds provide nectar in early spring; bare ground and plant debris are sites for bees to build their nests; leaf litter is shelter for overwintering bumblebee queens. We can refrain from using pesticides, which not only kill the target pest but also bees and beneficial predatory insects.

Gardens that cherish our native bees also welcome other pollinators, such as butterflies, and a myriad of other insects. Pollinator, predator or prey, each has a role to play in a healthy ecosystem. Birds visit such gardens to feed and raise their young on a rich diet of insect protein and seed from pollinated plants. These gardens are alive with color, movement and sound.  And a bee’s hum is a comforting sound. One that reassures us that bees are still in business, sipping nectar, collecting pollen and enriching our world.