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Thieves in Your Garden
by Pamela Ruch - October 2014

It’s late summer and the garden is abuzz: honeybees on the mint, bumblebees on the sunflowers, hovering flies alighting briefly on the thyme flowers. Inside the rose-of-Sharon blossoms, carpenter bees are scrambling around the pollen-coated stamens with ecstatic abandon, powder-puffing their ample bodies. There may be a pollinator crisis elsewhere, but in my garden there’s plenty of action.

 


Carpenter bees’ tongues are not long enough to pollinate the tubular flowers of Nicotiana sylvestris.

 

But wait — what is that carpenter bee doing to the nicotiana? I watch it as it systematically slits the base of each tubular flower so it can get at the nectar through a side door. The bee is perforating the tender tissue, and robbing the flower! That’s right, robbing. Taking nectar without paying the price.

Watching the native bee slit and sip, slit and sip, gets me wondering about how much of this sort of cheating goes on. I begin to notice thievery all over the garden — on buddleia, salvia and on native summer phlox. I watch big bullying bees roughly shoving aside the sexual parts of leadwort flowers and going right for the sugar. Following behind, and taking full advantage of the breaches to lap up the sweet remains, are honeybees. The very bees we import from Europe because of their industrious nature, those hard-working pollinators of almond, peach and apple orchards, are stealing nectar on the sly!

 


A puzzle: Individual bees of the same species get nectar from bean flowers in different ways.

 

There are, as it turns out, a slew of insects in our gardens committing “floral larceny.” Some find themselves without the proper equipment needed to extract the nectar through “legitimate” means, so they break and enter. Others simply follow behind, using the easy access holes created by thieves with sharper appendages. Ants, for example, are frequent secondary looters. Illegitimate visitors might also include wasps, beetles and even birds. Some might switch between pilferage and proper behavior on the same floral visit; others will rob one species and then legitimately pollinate another. As I watch two carpenter bees on a bean plant, I notice one mounting flowers with obvious ill intent while the other properly goes about her business.

 


Asclepias curassavica
: a favorite of butterflies and carpenter bees.

 

Carpenter bees, docile souls though they are (males may dart ferociously about your head but they don’t even have stingers), are among the most notorious of the nectar thieves. However, their behavior is not consistently felonious. I watch them guide their bulk into the generous flowers of scarlet runner bean, and navigate the miniscule blooms of lavender. I see them clambering aboard milkweed and cosmos, grabbing the flower heads with their forelegs and sucking for all they’re worth — all in a seemingly legitimate manner. In fact, they appear to eschew the nicotiana and phlox when these other options are available. This could be a matter of preference, or they might somehow sense that some caller has preceded them, and sipped the sweetness out of yesterday’s stale blooms. When I examine the calyxes of the nicotiana flowers, just about every one has an entry slit or tiny round hole. Some have both, presumably from two separate thieves.

 


Telltale signs of a nectar thief are slits and holes.

 

Our human code of conduct has established that nectar is a reward for services rendered. Our language suggests that access to it otherwise is ill-gotten gains. Every word I use to describe this behavior — thieves, robbers, cheaters, illegitimate visitors, felonious, pilferage, larceny — has been taken directly from the scientific literature. Each one implies wrongdoing.

And yet, life in the garden goes on. Flowers thrive; bees build their nests and raise their young. Is a crime really a crime if there is no victim? This argument has been going on, literally, for centuries. In 1872, Charles Darwin weighed in: “all plants must suffer in some degree when bees obtain their nectar in a felonious manner by biting holes through the corolla.” He speculated that when a plant species declined, and it no longer grew in crowded masses, the bees would begin again to enter “in a legitimate manner.” Equilibrium would be restored.

But the question of whether equilibrium is even upset by those who access nectar in a manner that does not benefit the plant in an obvious way has not been fully answered. Bees take what they need, and flowers are pollinated. We get apples, and almonds and plums. This is the story we tell our children as we try to puzzle out the roles of the unfathomable numbers of inhabitants with which we share our gardens. There are many possible twists to this simple plot. Pollinators may be prompted to change their behavior when “thieves” extract extra nectar for their young — they may move on more quickly than they might otherwise, which may lead to more cross-pollination. Or, flowers may stock extra nectar supplies to nourish a whole range of visitors. Indeed, some plants have extrafloral sources of nectar, just for those insects (ants, mostly) not very well suited for the job of pollinating.

Answers may come in time, but for now, two things are certain. First, when describing the behavior of non-human species, we should choose our words carefully; second, nothing in nature is as simple as it first appears.

 

Resources:
Irwin, R and others. 2010. Nectar Robbing: Ecological and evolutionary perspectives. Annual Rev. Ecol. Evol. Syst 41:271-92

Maloof, J and Inouye, D. 2000. Are nectar robbers cheaters or mutualists? Ecology 81 (10):2651-2661

 


Pamela Ruch is a horticulturist and garden writer living in Emmaus, Pennsylvania. She holds a master’s degree in environmental science from Green Mountain College. Currently the director of the Urban Garden at the Nurture Nature Centerin Easton, she teaches nature journaling workshops and hosts a website, Art of Nature Journaling.

 

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