Late summer flowers

pollinators, seed dispersal, and other end-of-season floral stories

One sunny day, I sat in a small meadow in the Kowee Creek drainage, just taking in the peacefulness and a snack. Some small, red-eyed flies found me and crawled over my arms, dapping at the skin with their nonbiting mouthparts—possibly tasting a bit of salt. Several of them had substantial amounts of yellow pollen on the thorax. All over the meadow, little white flowers showed their heads among the mosses and sedges. I knew these to be flowers of swamp gentian (Gentiana douglasiana). They were about a centimeter across, with odd little pleats in between the five white petals. Because they were the only flowers to be seen, I suspected that the flies are among the pollinators of those flowers—although I did not actually see them visiting the flowers.

What a contrast with the goldenrods that bloom along the road above Eaglecrest. There, on another nice summery day, the golden inflorescences were often thronged with visiting insects: flies of various sizes, a wasp or two, hoverflies, and bumblebees.

As I traipsed through another meadow, this time on the Spaulding trail, I saw tiny white flowers that were borne on branching stems that reminded me of wee candelabras. Looking more closely, I saw that each flower, only a few millimeters across, looked like miniature flowers of the swamp gentian flowers I’d seen earlier. Could this be the same species? The answer turned out to be Yes. By diligent searching, I found a few plants that bore single large flowers on one stem and acandelabra of tiny flowers on another. So I learned that this species produces flowers that vary two- or three-fold in flower size, apparently depending on how many flowers are borne on a stem. This suggests that there may be a trade-off between size and number of flowers per stem: more flowers, then small size; one flower, then large size—as if the plant had made some hormonal decision about how to allocate its floral displays.

In the muskeg ponds, buckbean flowers were finished and the seedpods were maturing. Some had opened, shedding their seeds onto the water surface. The seeds floated nicely, but the opportunity for dispersal by water was limited, because there was no surface-water connection among ponds. That would mean that all the buckbeans in one pond are closely related to each other—the seeds being genetically at least half like the mother plant. However, insects probably transfer pollen among plants in different ponds, increasing the genetic diversity within each pond while reducing the potential differentiation among ponds.

The big tall fireweed that is so common here is producing lots of fluffy seeds to blow on the breezes. That, however, doesn’t work when rain flattens those fluffy parachutes (into nets that are beautiful with captured raindrops). I wonder how many of those seeds get airborne. Landing in a suitable place is always a lottery, but getting into the lottery in the first place is a necessary step. Rain gets in the way of seed dispersal for these plants.

Some of the tall fireweeds still had some flowers and even buds at the top of the stem. Although most of the flowers are about the same size, on one plant I noticed flowers that were only about half of the normal size. Weird! I have read that drought conditions can lead to production of significantly smaller fireweed flowers, but that would not explain this single small-flowered plant. Then I happened to peer more closely within a normal flower (shame on me for not having done this sooner!) . First, I was reminded that fireweeds produce blue pollen; although blue pollen is known from a few other species elsewhere, it seems to be unusual here. That simple observation raises the immediate question: Why blue?

The flowers mature in sequence from the lower part of the inflorescence to the tip, where buds can still be found when the older, lower flowers have already produced mature pods. Within each flower, the pollen-producing anthers mature before the female-receptive surface (the stigma). The lengths of the male phase and female phase of each flower varies; the duration of the male phase is longer early in the season, when there are fewer female-phase flowers available to receive pollen and mating opportunities are few.

Fireweed is self-compatible, meaning that pollen from the same flower, or another flower on the same plant, can be effective in fertilizing seeds, although outcrossing, with pollen from different plants, also occurs. Perhaps because seeds can be produced either by selfing or outcrossing, fireweed flowers seem to produce pods very successfully. Furthermore, as a flower ages, the lobes of the (unpollinated) stigma bend back and down, bringing the receptive surface closer to the nectaries, where a visiting bee would be likely to forage, perhaps bringing in pollen and thus increasing the probability of fertilizing seeds.

The flowers have several means of increasing the probability of outcrossing. The difference in timing of male and female parts reduces the likelihood of pollen landing on the stigma of the same flower (but not between flowers on the same plant). The flowers start to close about four hours after pollination, well before any seeds are fertilized (it takes many hours for sperm from the pollen to reach the eggs in the ovary). The flowers close faster if outcross pollen is deposited than if self-pollen lands on the stigma (slower closing of selfed flowers leaves more time for outcross pollen to arrive), and faster if there is lots of pollen deposited than if few grains are deposited.

Photo by Bob Armstrong

Footnote: in a recent essay I commented that I had found marsh felwort only in two places. No sooner than I had written that, I found lots of the little blue, starry flowers in Cowee Meadows, mostly over toward the creek. Although this plant is an annual, it’s probably been there all along; I simply was not there are the right season.


Sound production by insects

taps, pops, and chirps, buzzes, clicks, and stridulations

Back in the Midwest, in the summers I listened to cicadas calling and crickets chirping—sounds that don’t happen here in Southeast. We hear mosquitoes and bees buzzing, of course, but that’s about all we hear from local insects. It gives us a very small sample of the sounds that insects can make, both within the audible range for humans and in ultra-high frequencies beyond our range.

Sometimes, insect sounds are made in response to disturbance, as a form of defense, startling or warning the attacker. Or they reinforce a visual similarity to potentially dangerous insects—thus involving both visual and acoustic mimicry. In other cases, the sounds communicate among members of the same species–males courting females, for instance.

Insects can make sounds in five principal ways. Perhaps the best know is by ‘stridulation’—rubbing one body part again another. This is how grasshoppers, crickets, some beetles, and certain spiders make noise. Different body parts are involved for different species: for example, in some species, special places on the front two wings are scraped together, or the hind legs are rubbed against the front wings, or two mouthparts are rubbed together. The ‘songs’ are mostly made by males, and may serve to bring the sexes together for mating or they may warn off competing males (clearly, they can only work in these ways if the recipients of the acoustic signals can hear; and various kinds of insects have ears on their legs, or antennae, or their bodies).

Some moths can stridulate too. Decades ago, scientists learned that certain moths are able to escape predatory bats by making sudden evasive movements when they hear the sonar of an approaching bat. Later research disclosed that these species of tiger moth and hawk moth were able not only to dodge the bats but actually jam the bat’s sonar with extremely rapid ultrasonic clicks. The moths create a sort of blanket of sound around themselves, so the bats cannot sense them clearly in the cloud of noise. The moths are reported to stridulate by rubbing their genital parts together.

Less dramatic acoustic signaling can be done by tapping some body part against the substrate. For instance, certain grasshoppers tap their feet, cockroaches tap the tip of the abdomen, and certain beetles bang their heads. Flies and bees buzz, using the flight muscles and wings. The buzzing of bumblebees and some solitary bees is important in the pollination of numerous plants: the buzzing releases pollen, which falls onto the bees, which then carry the pollen to another flower (this buzz is said to be quite different from an angry buzz). Male cicadas have special organs in paired cavities in the front part of the abdomen. In each cavity is a hard, ribbed structure that is vibrated by strong muscles, making rapid clicks; two membranes moderate the volume and type of ‘song’. Each species of cicada has a distinctive mate-attracting song.

The fifth main means of sound production by insects is by forcibly ejecting air or fluid from the body. Bombardier beetles eject from the anus a hot fluid that vaporizes when it meets air; the high temperature is generated when two different chemical substances are combined at the time of ejection. A popping sound accompanies the fluid ejection. This unusual system is a defense mechanism.

Sound production by forcible expulsion of air is said to be rare in insects. Although naturalists have previously known that hawkmoth caterpillars could make sounds—loud squeaks or whistles, only relatively recently have researchers investigated how these sounds are made, by studying the walnut sphinx moth caterpillars. The caterpillars have eight pairs of openings (called spiracles) on their sides; these openings are part of the respiratory system. By systematically blocking each pair of spiracles in turn, experiments showed that the enlarged openings of the eighth pair were responsible for the whistling sounds. The caterpillar forces the air out by contracting the front part of the body.

Further experiments showed that the whistles had a secondary defensive function called into play when an avian predator spotted the caterpillar despite its camouflage and pecked at it. Foraging birds such as yellow warblers were startled by the whistles and typically moved away. Further research found that these caterpillar whistles mimic the alarm calls of certain birds, such as chickadees, and the whistles kept these birds away from food sources.

There are undoubtedly numerous other nifty acoustic signals used by insects in various interesting ways. They are out there, waiting to be discovered.

Stories behind the names

the faraway origins of some local plants’ English and scientific names

‘Twas the last day of July, and the big meadow at Eagle Beach State Rec Area was decorated with white flowers. Tall, flat-topped inflorescences of cow parsnip ringed the edge by the trees. Shorter and lacier inflorescences of hemlock-parsley came next and filled an area near the old dunes. On slightly lower, more central ground, the single flowers of northern grass-of-Parnassus spangled the field. And weedy little yarrow fit itself in wherever it could.

Photo by Bob Armstrong

This grass-of-Parnassus (Parnassia palustris), also known as bog star, has a wide geographic range across North America and Eurasia. Inside the saucer-shaped flower are five stamens bearing pollen, five staminodes (sterile stamens) that bear droplets on their branched tips, and a single ovary with a stigma where pollen is deposited. The droplets do not contain nectar but may help attract small flies and bees that do the pollination. Nectar is produced at the bases of the stamens and staminodes, according to a scholarly report (resolving the contradictions and confusions found on general internet sources). Insect visitations, moving pollen within a flower or bringing it from another one, are reported to be necessary for pollination and seed set. Seeds are spread by wind and water.

The taxonomy of Parnassia is confusing too. Our field guides place the genus in the family Saxifragaceae. However, several internet sources place it either in its own family or in the family Celastraceae (along with burning bush, Oriental bittersweet, and others).

I was interested to learn how this plant got its English name. It’s not a grass, so that is a misnomer. But what does Parnassus have to do with this plant?– the name appears in both the common and the scientific names.

Mount Parnassus is a fairly large mountain in Greece, not as big as Olympus and not as important in mythology. Nevertheless, in ancient Greek mythology, Parnassus was sacred to Dionysus, the god of grape harvest, wine, debauchery, and madness. The mountain was also a sacred haunt of Apollo, who was a multifaceted god of light, music, town-building, and prophesy—and a hero, a protector of flocks and crops, a lecher, a bisexual, and an archer. Parnassus was also visited by the Muses—goddesses of song, poetry, history, and dance, as well as other minor deities.

Then, about two thousand years ago, a Greek physician and botanist named Dioscorides wrote a huge set of books on medicine, useful plants, and related matters. He wrote in Greek; his books were translated into Latin and Arabic and, eventually, into other languages. They constituted the basis of the practice of western medicine for centuries. Supposedly, Dioscorides gave grass-of-Parnassus its name, having found it growing on the Mountain. I have no access to this doctor’s original opus, but it seems unlikely that he really confused this plant with the grasses; perhaps he merely said it was like a grass in some way. Then, somewhere along the line, some taxonomist just decided to apply the inappropriate name of grass when naming this species.

The generic names of two of the other white flowers in the meadow also hark back to Greek mythology. Heracleum lanatum (cow parsnip) refers to Heraclites (Hercules, in Latin)—known for his prodigious strength. As penance for his crime of murdering his wife and children in a fit of madness, he was given the fabled twelve Labors of Hercules (killing or capturing some monsters, cleaning the Augean stables that were full of manure, etc.). The very robust plants of cow parsnip might reflect his strength.

Achillea millefolium (yarrow) is related in name to Achilles—he of the vulnerable heel. Legends say that Achilles’ mother held her baby by a heel and dipped him in the river Styx to make him invulnerable, but the heel didn’t get wet, leaving it unprotected. After many adventures, including killing Hector in the Trojan war, Achilles was killed by an arrow in this heel. Yarrow indeed has good medicinal properties, but the tales telling that Achilles used this herb to heal wounds may be apocryphal.

Before I leave Greek mythology, here are two more quick examples; both are orchids with representatives in Southeast. The genus Cypripedium (moccasin flower or lady’s slipper) is named for the foot of Kypris (later known as Aphrodite in Greek, Venus in Latin; the ‘ped’ refers to foot in Latin). In variable forms, she was the goddess of love and lust, beauty, fertility, and marriage. Calypso bulbosa (fairy slipper) is a showy orchid. The ‘bulbosa’ part of the plant’s name refers to a bulbous corm at the base of the plant. In Homer’s epic poem, Calypso was a goddess-nymph who successfully seduced Ulysses (Odysseus in Greek) for seven years. Perhaps she was really bulbous when bearing two children by him!

And how do all these mythical creatures get into taxonomy at all? Well, one reason is that, historically, all young scholars, including future taxonomists, were well schooled in Greek and Latin classics, so the names and stories were very familiar to them.

Disruptive Coloration

hiding in plain sight

Just above a stony beach on the way to Lena Point, a patch of yellow paintbrush caught my eye. Inspecting one of the blossoms, I found a beautiful little green caterpillar lying in the curve of one of the outer bracts. It had a narrow white longitudinal line down its back. If that caterpillar had rested on a green leaf or petiole, perhaps the conspicuous white line would draw a predator’s attention, distracting it from the whole body of the caterpillar. Furthermore, that white line would have disguised its real shape, visually dividing it into parts that could seem to be unrelated to each other. And thus, a caterpillar-hunting bird might pass it by.

Patterns that visually break up the shape of an animal’s body are called ‘disruptive coloration’, a common anti-predator ploy of many animals. If it is to work as designed, the animal must behave in a way that suits its pattern. However, this little green caterpillar on a yellow bract was not behaving in a way that best utilized its color pattern. (Maybe it would get away with this apparent mistake by being somewhat concealed within the curved bract.)

Disruptive coloration is often combined with some form of color-matching, such that just part of an animal matches the background (if that caterpillar had been on a green stem, for instance). The blotchy browns on the back of an incubating female mallard might generally resemble a heap of dead leaves. The camouflage effect would be enhanced if the blotches obscured the outline of the sitting duck and even more so if some of the blotches matched the area around the nest.

The optical tricks of disruptive coloration take many forms—not just any color, nor any pattern, nor any arrangement of tone will do. First of all, the effect of a disruptive pattern is enhanced when the color of some patches match the background (as noted above for the mallard) and other patches differ markedly. This makes some parts of the animal fade away visually, while others stand out. In addition, the disruptive effect is greatly intensified if contrasting light and dark tones are adjacent to each other; the more conspicuous patches dominate a predator’s vision, letting the true shape of the prey animal fade back. These effects are strongest if the transition from light to dark tones is sharply defined and not gradual.

A further complexity is provided by a false appearance of relief: colored patches appear to be at different levels or perhaps sloped. This can be accomplished by gradations in tone and is more effective when a light patch becomes still lighter and an adjacent dark patch become still darker at the place where the two patches meet. This illusion can make a flat surface look three-dimensional, or a rounded surface look flat, distracting an observer from the real shape.

Breaking up the body outline may sometimes be accomplished in unexpected ways. For example, experiments have suggested that contrasting marks along the edges of butterfly wings may make the wings less recognizable to avian predators, and thus reduce the risk of predation. Sometimes, color patterns seem to tie disparate body parts together—uniting discontinuous parts; in short, this is the opposite of breaking up a continuous surface or outline. For example, the dark bands on the legs of some frogs seem to merge with similar bands on the body when the legs are folded, so a frog becomes a banded lump with no apparent froggy legs.

All of these delusionary optical tricks are well-known to artists. However, I’ve read that those who use camouflage for military or hunting purposes were initially very reluctant to believe them and so required a lot of persuasion. Of course, Mother Nature has been doing these tricks via mutation and natural selection for eons.

That’s a lot of words sparked by seeing one little caterpillar! And I haven’t even touched on the more famous ways of hiding in plain sight, such as looking like a stick or a leaf or a bird dropping or a bit of algae or some dangerous critter or….Another time, perhaps.