Spurs: Hard to Get Nectar

Violet.

© Beatriz Moisset

 Many flowers are very particular about their clientele. They have developed ways to make themselves attractive to certain flower visitors while discouraging others. They do so by adopting a certain shape. The spurs of many flowers serve this purpose. A petal or a sepal develops an elongated hollow spike. This is what botanists call a spur.

Violet (Viola mirabilis). Note the spur

Wikicommons. © Antti Bilund

Violets have a spur. Nectar is collected at its bottom. A pollinator needs a tongue long enough to reach the hidden nectar waiting in this special vessel. The rest of the flower is so designed that the insect gets covered with pollen while performing this task. If it is carrying pollen from a previous flower visit, it is likely to deposit it on the stigma. Only long tongued insects can take advantage of this flower and they need to develop an efficient way to approach this specially shaped blossom. After a few times they get better and better and proceed faster. The most common pollinators of violets are small, solitary bees.

Bumble bee visiting a jewelweed blossom

© Beatriz Moisset

Jewelweed (Impatiens) also possess a spur. The flower itself is a small chamber just a little larger than a bumble bee. The petals form a curtain that slightly blocks the entrance to this chamber. Bumble bees are pros at collecting nectar from these flowers. Their plump bodies fit inside the chamber like a finger in a glove and their long and flexible tongues are suited to the curved spur.

Columbine.

© Beatriz Moisset

Columbines have not one but five spurs. Each petal is shaped like a long hollow horn ending on a knob. This is where the nectar gathers. Long tongued insects and hummingbirds pollinate these flowers. In most species, the flower nods or points downward, and the spurs point to the sky. This arrangement seems to be agreeable to their most common pollinators, hummingbirds.

Columbine.

© Beatriz Moisset

By contrast, the flowers of the alpine columbine remain erect, don't nod. They are also creamy white, a color favored by moths. And thus, they are preferably pollinated by large moths, the so called hawkmoths. A few other species of columbines, including the Colorado blue columbine, also face upwards and are also pollinated by moths.

Columbine and carpenter bee

stealing nectar

© Beatriz Moisset

Jewelweed and ants

stealing nectar

© Beatriz Moisset

This specialization has advantages but it also has some disadvantages. Not all flower visitors behave like honest pollinators. These difficult flowers are an invitation to cheating. Some visitors learn to take a shortcut, especially if their tongues aren't long enough to reach the bottom of the spur. They approach the flower from the side. Perhaps, they can smell the sweets through the walls of the spur. A quick bite or a stab through the delicate petal may be all it takes to reach the hidden food. Carpenter bees, bumble bees and even ants have been seen performing this robbery.


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Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2017

Ants, the Unlikely Pollinators

© Beatriz Moisset

Ants are seen visiting flowers with great frequency. People often ask me: Do ants pollinate? I answer with another question: What do you think? Are ants capable of pollinating flowers? Do they have what it takes to carry pollen from one flower to another, preferably of another plant?

Ants stealing nectar from the spur of a jewelweed. © Beatriz Moisset

Most pollinators can fly from plant to plant. Ants, lacking wings, don't go very far. Moreover, ants may be coated in some sort of antibiotics which may be detrimental to pollen. In some cases ants steal nectar from flowers, causing damage and reducing the likelihood of later pollinators' visits. Some plants resort to extrafloral nectaries, nectar-producing glands located in other plant parts, to keep the ants and other nectar robbers away from the valuable treasure reserved for legitimate pollinators.

Ants pollinating wood spurge. © Beatriz Moisset

Despite all these drawbacks, there are instances in which ants are pollinators. One case is that of spurge, or Euphorbia. This plant grows very low near the ground and tends to intertwine its runners with those of nearby plants. This increases the chances of ants going from the flowers of one plant to those of another without the need to fly. Perhaps the pollen of spurge is more resistant to the chemicals on an ant's body. So, ants pollinate spurge; although, there are also small bees that perform this job just as well.

A few other plants, also low-growing, are pollinated by ants. Finally, there are some interesting cases of orchids pollinated by ants in Australia in a highly specialized way. So, yes, ants join the ranks of pollinators. They may even be the pollinators of choice for some plants in harsh, dry climates.

Ant on Queen-Anne-lace. © Beatriz Moisset

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Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2012 

Robbers and cheaters and innocent bystanders

Bumble bee robbing nectar

Some flower visitors don't hesitate to rob nectar without paying their dues. They either don't bother or can't enter the flower the "legitimate" way, and thus, ensure picking up pollen along the way and delivering it to the next flower. Instead they take a shortcut, slashing the throat of the flower and going right to the source. Carpenter bees can be among the most notorious robbers because of their strong and sharp mouth parts that enable them to perforate the walls of a flower; but other large insects can be just as bad.

Abelia flowers with slashed throats

Tubular or trumpet shaped flowers are the most frequent victims of this larceny because their nectar is hard to reach. Here are some abelias that have been robbed. You can see the scar at the base of the flower.

Sometimes smaller bees or other insects take advantage of the shortcut and visit the wound, like this beetle, which also happens to parasitize the nests of bumble bees.

Sap-feeding beetle Epuraea aestiva

 In this case something more tragic happened. A small bug ventured deep inside the flower and became tangled, its legs sticking out of the hole, and unable to go in or out or turn around. I thought that I may be able to help it and by the way find out the identity of the victim; but my clumsy old fingers couldn't perform this delicate task. I never found out who this innocent bystander was. Any guesses?

An insect trapped inside the flower

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Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2012

Partners and Robbers

A jewelweed blossom is worth examining carefully; it is a little marvel of engineering, with a shape perfectly adapted to its pollinator, a plump bumblebee with a very long tongue and a thirst for nectar.

The shape of the little sac fits the body of the bumblebee like a glove; the side petals open like a pair of curtains to allow its entrance; the length of its spur, full of nectar is just right for the tongue of the bumblebee. And, finally and most important to the plant, the anthers (that carry the pollen) and the stigma (which receives the pollen) are placed so that the hairy back of the bumblebee rubs against them when entering the flower. The pollen is deposited on the bee and later on it is transported to other flowers.

For pollination to take place the bee has to enter the front of the flower otherwise it would fail to touch the parts of the flower that matter.

Despite this marvelous system, some very nice pollinators can turn into robbers and cheat the flowers that they usually serve diligently. This happens when the pollinator chooses to take a shortcut and bypass the well planned scheme of the flower. Such is the case of this bumblebee. When it takes nectar by slashing the spur from the outside it doesn't come near the pollen carrying organs and doesn't perform pollination.

Pollinators: Robbers and Thieves
List of articles

Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2012