BY SHARON REEVE, UCCE MASTER GARDENER OF SAN DIEGO COUNTY
Plants are anchored in one spot, but they are cunning. They have mastered the art of enticing more mobile organisms to do their bidding. It is the goal of every living thing to procreate and to live on through their offspring. Plants are no exception. There are many pollination strategies employed by plants. Wind pollination is highly inefficient, and self-pollination does not allow for evolution, so many plant species have evolved to entice and use insects and animals to pollinate themselves. One of the strategies used by plants to lure pollinators is to supply nutritious, high-protein pollen in the hopes that some of the pollen is not eaten but taken to other plants for pollination. Many plants also produce sweet nectar to lure in animals. Everyone loves sweets, as do insects, animals, and birds. Plants make sweet nectar to attract visitors to their flowers with the ultimate goal of the visitors accidentally carrying male pollen to the female stigma of another plant of the same species. Some orchids even go so far as to create structures that look like female bees to attract male bees. Male bees fooled by these look-alikes will attempt to copulate with them, and, in doing so, will spread the pollen of the orchid. This trickery is a cost-saving measure in that the orchid does not have to manufacture nectar or prodigious amounts of expensive pollen. While bees are the main pollinator of plants, there are other organisms that augment pollination, namely butterflies, hummingbirds, flies, wasps, bats, and beetles. Here, we focus on butterflies, flies, and bats.
Butterflies are the flashy members of the order Lepidoptera. Many of them have evolved to use highly toxic plants as caterpillar host plants to keep from being eaten. Bright colors also advertise sexual fitness, serve as camouflage, or mimic other more toxic butterflies. In the animal kingdom, orange is the color of danger and is frequently employed by butterflies. Dark wing colors act as solar collectors to warm the butterfly on cold days. Butterflies can see in the UV light spectrum. The pigmented scales that make up the wing can also look very different under UV light. Plants frequently have markings only visible in the UV spectrum that advertise the location of nectar and pollen. Butterflies use their long, coiled proboscis (mouthpiece) like a straw to sip nectar. Plants with wide, flat flowers like California native buckwheats (Eriogonum sp.) are choice nectar plants for many butterflies.
We think of pollination occurring during the day, but there are a number of organisms that pollinate only at night. Bats and moths take over when the sun goes down. In the dark of night, color and scent become incredibly important, which is why bat-pollinated plants bloom primarily white and are very sweetly scented. Bats are effective pollinators as they are able to transport large amounts of pollen on their furry bodies. Plants have evolved to hang away from the plant to give easier access to incoming bats. In plants like agave, pollen and nectar structures are prominently displayed along the huge flowering structure the plant makes before it dies. Agaves only bloom once, and when they do, they grow a bloom spike that is several times larger than the plant, sometimes as high as 15 feet. This is a massive investment of energy and the final chapter in this plant’s life. Agave tequilana (the source of tequila) pollen is especially nutritious and 50% protein, while the nectar keeps bats flying with 22% sugar.
Not only do plants produce nectar for pollinators, they can also create scents that are irresistible for their pollinator of choice. For example, flies feed on carrion, and plants in the genus Stapelia bloom accompanied by the stench of rotten meat. It isn’t really rotten meat, only the plant that has refined the scent of its flowers to attract large quantities of flies to pollinate. I have many species of Stapelia in my garden and when they bloom they attract a steady influx of flies. This strategy to attract flies is not limited to only the genus Stapelia as other members in the family Araceae do this. In fact, the aptly named skunk cabbage has the ability to raise the temperature of its flowers to make them smellier while it is blooming.
While plants look demure and defenseless, they are actually mighty and clever, with marvelous and wondrous ways to assure pollination.
Sharon Reeve has an MS in ecology. She is a landscape designer specializing in wildlife gardens.
CunningPlants Use Tricks to Lure Pollinators originally published in the winter 2022–2023 issue.