Drama on the Flowers

by Carlos de la Rosa
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Ant holds bee by leg. Gotcha! The ant is holding this flying bee by the leg. If lucky, the bee will get away. This bee has already lost part of a leg to a previous similar encounter.

The bright yellow flowers of the goldenbush (Isocoma menziesii) nod in a gentle afternoon breeze. It is late fall on Catalina Island and the splash of color catches your eye. Up close, a whole production is unfolding. Numerous bees hover over the expanse of flowers, a butterfly awkwardly scuttles off to visit the delicate flowers of the narrow-leaf milkweed (Aesclepias fascicularis), a fly struggles to extract itself from a spider’s web, and ants are swarming on the flowers and running up and down the stems of the plants. What else is going on? Several dramas unfold every day in and among the flowers of Catalina’s plants. These interactions between plants, insects, and animals illustrate a number of ecological concepts in quite dramatic and interesting ways. It’s the true theater of life, filled with danger, heroes and villains, sex and death, a struggle to survive, natural selection at work, a battle of tiny jaws and claws repeated endlessly day and night.

The first concept one can explore is that the more complex the flower, the more likely it is that it evolved specifically for a species or group of insects for pollination. And, the insects more than likely have developed characteristics that maximize the benefits from these specific plants. This joint evolution, a form of an “arms race for reproduction,” is known as co-evolution. Many plants reproduce sexually by producing male and female “gametes” in the form of pollen and eggs that when joined will form the seeds for the next generation. Sexually reproducing plants use flowers in the production and packaging of these gametes and many of these flowers use insects as the means to transport their gametes to other flowers. A pollen-laden insect is a great reproduction messenger, bringing the pollen from flower to flower ensuring that a plant will not self-pollinate, something that for some plants is not a good thing

Ladybug eating an aphid. Ladybugs are fierce predators of aphids, the yellow insects sucking sap from the stem of this plant. Both, the larva and the adult of the ladybug feed on aphids. Lunch time for ladybugs. Aphids multiply very fast and can eventually harm the plant they are feeding on. Ladybugs eat the aphids, but often not fast enough!

These plants have evolved in ways that attract and reward their insect visitors, particularly those that get involved in the transport of pollen to other flowers. The sweet and often not-so sweet collection of scents produced by flowers act as attractants to a variety of insects and birds, like hummingbirds. Some smells are quite disagreeable to us humans, like the smell of rotting meat produced by some flowers of certain succulent plants. Why would a plant smell like rotten meat? To attract flies, of course! And flies get fooled and walk around the flower looking for the piece of decomposing flesh and in the process pick up a lot of pollen that they take to the next flower. A cruel deception, you may think, but it must work for both the flower and the fly, because it keeps happening and evolving and it is fairly common in nature.

 

Bee with pollinia drinking nectar. Bees, such as honey bees and other species, visit flowers not only to drink their nectar, but also to collect pollen, which they use as food back in their nests for their growing larvae. This bee drinking nectar from a milkweed flower also has accidentally collected the flower’s pollinia, or pollen sacs, which can be seen as yellow structures attached to the bee’s legs.The bee will carry these sacks to the next flowers it visits.

Color is also an important attractant, although insects and even birds see color differently than us. Many insects, for example, can see into the infrared region of the color spectrum, something we can’t detect with our naked eyes. So a flower that to us looks uniformly yellow can appear very different to an insect, with contrasting patches, lines, “landing zones” and other features that we can only see when using ultraviolet light and a camera that can see UV. And then there is the reward: nectar. The word nectar encompasses a suite of sugars (mostly sucrose, fructose and glucose) produced by specialized glands called nectaries. Most of the nectaries are found in flowers, although they can also be found on leaves, pedicels of leaves and other locations on plants. Nectar is an important source of energy for insects such as bees, butterflies, wasps and ants, as well as birds like hummingbirds and many species of bats.

We now have the ingredients for an all-out war. With a smörgåsbord of scents and colors and the sweet loot of nectar, a broad assembly of pollinators and opportunist, predators and potential prey will gather around the colorful battlefield. Where there is nectar, there are nectar-feeders, and where these are, there is likely to be a predator around. This is the next piece in the complex web of life. Spiders, ants, praying mantises, wasps and other creatures, including lizards and frogs, hang around flowers because of the abundance of potential prey. Some, like Argentine ants, attack insects visiting the flowers either to catch and kill them or to defend other plant-associated resources, such as aphids, from which they obtain benefits (the so-called honey-dew aphids exude for the ants). And often there will be competition for the nectar, doled out in small quantities by the flowers.

And so we go back to the goldenbush flowers of the introduction. Argentine ants (Linepithema humile) have claimed the territory for themselves. They are nectar hogs, not the sharing kind of creature. Any bee that approaches a flower will get rushed and attacked as an intruder. Argentine ants are not native to Catalina Island. Originally, they come from northern Argentina, Uruguay, Paraguay, Bolivia and southern Brazil and have become invasive in the US, displacing many native ants. Our native bees are not used to the Argentine ant’s aggressive behavior. The bees land on the flowers and as they begin to sip the nectar, the ants confront them and injuries occur. I photographed several of these interactions, finding a number of bees with missing legs or segments of legs that had fallen prey to the bellicose ants. And if losing a limb or two wasn’t bad enough, their nectar-gathering time gets also severely reduced. A bee that would normally spend a 10 or 20 seconds exploring the flower head and sipping the nectar can only spend a second or two before getting mugged by the ants. This reduces not only its fitness and ability to forage efficiently, but also reduces the fitness of the goldenbush because the bees can’t get enough pollen on them to go to the next flowers.

Argentine ants attack bee. A swarm of Argentine ants on a wooly sunflower will prevent insects from landing and drinking the flower’s nectar. Some may even lose their lives to the ants. Here, a sweat bee lands on the wooly sunflower to collect nectar. The ants make their move and start swarming towards the bee. The attack is swift and efficient. The bee has precious few seconds before an ant gets a hold of it, which could lead to harm or even death.

We can only wonder what the long-term effects of these changes in the relationships between ants, bees and flowers will bring. Invasive species, a topic for a separate essay will be explored in more detail another time. Suffice to say that Catalina is a fertile ground for active evolution and natural selection, some prompted by the effects of human activities, others by the global changes we are experiencing in climate. It is an evolving story and we could use more researchers to help us understand what beneficial role we could play in this ongoing drama.

 

Milkweed bug on milkweed. A milkweed bug, bright in its warning colors that say “Don’t eat me! I taste really, really bad!” doesn’t drink the nectar of the narrow-leaved milkweed flowers but pierces the stems of the plan with its sucking mouthparts and drinks the sap, probably the main reason why it tastes so bad!