The first Pollinator Week was observed in 2007 in America after the Senate’s unanimous approval of a resolution that acknowledged the week as a necessary step in recognizing the urgent issue of declining pollinator populations. Pollinator Week is an annual event celebrated all over the world in the last full week in June. The event is organized and conducted in support of pollinator health by the Pollinator Partnership.
The week is observed as an international celebration to protect the ecosystems that sustain all pollinators – be they bees, flies, wasps, beetles, moths, butterflies or hummingbirds.
As we continue this weeklong event, let’s focus on one that most of us probably do not think of as a pollinator of flowering plants – butterflies.
The pollinating butterfly families are mainly skippers (Hesperiidae) and common butterflies (Papilionoidea).
Second only to bees as a pollinator, butterflies have color preferences with purple, yellow, white and orange blooms being the top choices. Butterflies are less efficient than bees at moving pollen between plants. Highly perched on their long thin legs, they do not pick up much pollen on their bodies and lack specialized structures for collecting it.
However, when it comes to cotton (genus Gossypium), butterflies play an unexpected role. A recent study revealed that 40 bee species, 16 fly species, and 18 butterfly species visited cotton flowers at different times throughout the day. Flies would be out early, perhaps because they tend to nest in the fields. Then, butterflies would arrive; by the time the day’s temperature became quite hot, bees were out in force. Researchers also discovered that various insects tended to visit different parts of the cotton plant. Bees preferred to forage on inner flowers, closer to the main stem. Flies and butterflies landed on outer flowers, possibly because they’re less nimble fliers. These preferences essentially mean roughly 50% more flowers are visited, thanks to flies and butterflies, than if bees were the only pollinators. This phenomenon, which goes by the technical term pollination complementarity, isn’t unique to cotton. In almond orchards, wild bees and domesticated honeybees visit different parts of the trees. Complementarity could be more common than currently realized. (SOURCE: S. Cusser, Haddad, N. M., and S. Jha. “Unexpected functional complementarity from non-bee pollinators enhances cotton yield” Agriculture, Ecosystems & Environment. Volume 314, 107415, ISSN 0167-8809, https://doi.org/10.1016/j.agee.2021.107415 (2021))
Butterflies probe for nectar, their flight fuel, and typically favor the flat, clustered flowers that provide a landing pad and abundant rewards. Butterflies do not have any chewing mouthparts. Instead, they eat by sipping liquids, most often nectar, through their proboscis. A butterfly’s proboscis can be found curled neatly on the lower side of the head when the butterfly is not eating. When a butterfly does eat, the proboscis is extended through hydrostatic pressure into a relatively straight “straw” which it can then insert into the deep tubes of a flower in order to sip the nectar.
SOURCE: From landing lights to mimicry: The molecular regulation of flower colouration and mechanisms for pigmentation patterning – Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/A-UV-visible-nectar-guide-Photography-of-Rudbeckia-hirta-in-either-visible-left-or_fig3_230730335 [accessed 19 Feb, 2023]
Butterflies have good vision, but a weak sense of smell. Unlike bees, butterflies can see red and they also see ultraviolet light, which makes flower markings very distinct to them; those flower markings, called nectar guides, direct the butterfly to the nectar source on such flowers.
Nutritionally, nectar serves as a source of water, carbohydrates and amino acids for butterflies; the latter allows them to meet their nitrogen requirements. Interestingly, butterfly-pollinated flowers tend to have higher concentrations of amino acids than do flowers pollinated by bees and other animals. This is remarkable since insects like butterflies, whose larval stages feed on plant foliage and adult stages on nectar, have long been assumed to obtain most or all of their nitrogen-rich compounds needed for reproduction from larval feeding. Going against this assumption, it has been shown that both nectar consumption and larval food intake can affect the life span and fecundity (number of offspring produced) of some butterfly species. For example, a study found that nitrogen-rich compounds (amino acids) present in nectar significantly increased the fecundity of the nectar-feeding butterfly Map (Araschnia levana), which is found in Europe, Asia and Russia. However, it was enhanced only if the female fed on a poor-quality plant as a larva. Therefore, this suggests that nectar can act as a necessary dietary complement if a butterfly fed on a nitrogen-poor plant as a larva. (SOURCE: Mevi-Schutz J, Erhardt A. Amino acids in nectar enhance butterfly fecundity: a long-awaited link. Am Nat. 2005 Apr;165(4):411-9. doi: 10.1086/429150. Epub 2005 Feb 11. PMID: 15791533.)
Each species of butterfly has a particular host plant and nectar plant, the former being the plant on which it lays its eggs and caterpillars eat, and the latter being the plant from which butterflies drink nectar. This is why it is extremely important to conserve the native biodiversity of each ecosystem; if a butterfly species loses either its host or nectar plant, it can no longer survive and vice versa.
As the only butterfly species that completes a two-way migration, Monarchs (Danaus plexippus) from as far north as Canada set out on a fall migration to glide south until they reach the oyamel fir forests of Michoacán Mexico. Individual butterflies live four to five weeks on average, so it is their descendants—most likely their great-great-grandchildren—that will return to the northern states in the spring and complete this epic journey. Accordingly, these unique and wondrous butterflies are a cultural icon in each nation comprising North America. Read more.
Today, take a moment to stop and watch these graceful floral visitors and acknowledge their essential contribution in pollinating so many plants that we humans rely upon for food. Please check out Pollinator Week and Pollinator Partnership for brochures, resources, and suggested activities to learn how each of us can help ensure that these beautiful pollinators will forever be part of our world.
Curious By Nature 