September 27, 2005

On my woodland walks the past few days with Daisy, I have noticed many changes. Last week, the forest floor was pink with the leaves of the many Virginia creeper vines; today, those have turned brown and fallen, revealing the rosettes of next year's pussytoes, rattlesnake plantain, and numerous other small shoots of plants that will over-winter above the ground. Tree leaves will soon cover these with a snug blanket, but for now, only the elms and walnuts seem to be dropping foliage. Also shrub leaves are falling expanding the vistas and I can often see out to the surrounding hills.

Acorns crunched underfoot on many of the trails. The deer, squirrels, turkeys and other large birds will find plenty to eat, and many will be gathered for the long winter ahead. I heard a birder talking last week on the radio about the blue jay and its capacity for these nutritious seeds. Jays have pouches inside their mouths that allow them to carry off four or five acorns at a time that they hide for later consumption. Carter Johnson and Curtis Adkisson, in their article, Airlifting the Oaks, (Natural History, 10/86: 41-46) documented the oak planting abilities of these birds. They discovered that 50 jays transported and cached 150,000 acorns in 28 days, about 110 acorns per day for each bird, scattering their storage sites over a large area. They noted that although these birds have very good success in retrieving the majority of the seeds that they hide, those acorns not dug up have an excellent chance of germinating, as they are usually deposited in soft damp soil, ideal for growing oak seedlings.

Lots of other seed types can be found in the woods and fields, and burs of tick trefoil, avens, and other stick-tights adhere to our pant legs and socks, as well as to Daisy's long fur. Only the asters remain in full bloom. The uniqueness of the aster family is that each flower is actually a composite of many smaller flowers. If you pull apart the tight center, you will find dozens of miniscule yellow flowers growing on a disk, each with 5 tiny petals fused together, plus 5 stamens fused around a pistil. The big "petals", or rays as they are more properly called, that surround this disc are also flowers, with their petals fused together and hanging to one side. Some flower species will have either disk flowers or ray flowers, but our native asters have both. Each of the disk flowers will make one seed which, with its neighbors, will form a fluffy head of feathery white structures that help the seeds to be carried off by autumn winds. When the seeds are gone, all that remains is a pitted disk.

There are dozens of aster varieties, all with similar looking flowers, and varying only is size and color. Some may be an inch across while others are tiny fractions of that. They are usually white or blue, with a scattering of pink. Generally the species is identified by the shape of its leaves, although this method sometimes cannot be depended upon either, as the larger leaves on the stalk often dry up before the plant blooms. Our showiest native is the New England aster, which may reach 4-5 feet in height and is covered with lavender or sometimes pinkish blossoms. It obviously has lots of pollen as the blooming plants are alive with bees.

There are only a few white snakeroot plants blooming here and there, while last week they were common all along the trails. These are late summer plants that grow to about 2 feet with clusters of fuzzy white flowers, and are members of the daisy family, along with asters. The plant contains a toxic substance called tremetol, that can be transferred to humans via the milk given by cows that have eaten large quantities. I have not noticed that our plants are ever grazed so perhaps the wild animals have the sense to avoid it, but I read that it can poison cows, sheep, horses, and goats.

Moles and other burrowing animals have been busy preparing for winter, and I have to watch my step as I collapse tunnel after tunnel on the trails. They have been particularly active in the areas around the farmyard that we have kept watered, as the soil is soft and easy digging for them.

Some trees have lost their leaves early, presumably because of the drought we have been experiencing, and the aspens and some of the nut trees are turning a rather sickly yellow instead of their usual gold. We may not have the dramatic autumn show to which we are accustomed, but a few maples are showing their brilliant reds and rain is forecast, so perhaps all is not lost.

September 20, 2005

We finally received some rain this past weekend after several storms passed us by earlier this month. The effects of the lack of soil moisture had become very apparent; some trees were coloring and dropping their leaves prematurely, annual flowers not receiving supplemental water were drying up and dying, and many perennial plants were drooping as they tried to conserve what moisture they contained. Luckily, the growing season has almost finished, but concern was increasing for the survival of many of our plants over the winter if the drought persisted into the winter freeze-up. The problem, of course, is not really with the weather, but with our persistence in attempting to grow plants that are not tolerant of the vagaries of our climate.

The availability of water is undoubtedly the most important feature in any landscape, The Eastern part of the country before settlement was mostly covered with dense forest, because sufficient rainfall allowed trees to flourish. The states west of the Mississippi River became progressively drier, and first the hardwoods and finally even the aspens and cottonwoods could not survive, allowing the prairie grasses to predominate. Midwest states were mixtures of forest and prairie, and although much of the time rains were predictable and plentiful, periodic droughts killed off many of the trees and other plants, keeping much of the landscape open. The plants that survived developed a number of characteristics that allowed them in survive in times of low moisture.

All plant leaves are covered by a layer of close-packed cells, sometimes with a waxy outside coating, which prevents water loss and acts as a barrier to fungi and other invaders. The leaves "breathe", or transpire, through tiny openings in this surface layer that allow water vapor and other gasses to move in and out, and are regulated by guard cells. Normally the pores close during the night but must open in the morning for photosynthesis to occur. This exposes the plant to the risk of drying out as some 90% of the water taken up by a plant through its roots is lost in transpiration, and hot, windy conditions, especially when accompanied by low humidity, can cause difficulties. When soil moisture is insufficient to keep up with transpiration, a plant reacts by producing a hormone, abscisic acid, which will also close the pores. The leaves on most prairie plants have additional adaptations: some are long and thin, particularly the grasses, which reduces the leaf area from which moisture can escape; some have compound or deeply cut leaves, reportedly a strategy that lowers the temperatures on leaf surfaces; some have fuzzy or hairy leaves that reflect intense sunlight and also decrease evaporation; and most will roll up their leaves to reduce exposure to the hot sun and save moisture.

More importantly, two-thirds of a typical prairie plant is underground. The top few inches of prairie soil is filled with a tangle of plant roots, and other underground plant parts which make a layer of thick fibers that holds the earth tightly together. Grasses form root-like structures called rhizomes, really underground stems, which spread through the soil just beneath the surface in order to take advantage of any rain that does fall. The rhizomes store nutrients and send up new grass shoots each year. Grasses are very distinctive plants. They have narrow leaves and hollow, jointed stems. Their flowers are borne on spikes, and although they do not have petals like most plants, their pollen-laden stamens are held high above the ground to catch the wind. They have easy names that often describe some defining characteristic: big bluestem, also called turkey-foot grass; little bluestem; prairie dropseed; sideoats; June grass; Indian grass. The flower stalks usually begin to appear in late July and early August and some reach up to 9 or 10 feet. Later, beautiful grain-like seeds take the place of the flowers.

Prairie wildflowers seldom have to compete with the grasses for moisture because they usually send their roots much deeper into the ground. Wildflower roots may go down ten feet or more, and some reach to over twenty feet. In times of plentiful rains, growth is lush and flowers are abundant. During drought cycles, plants may remain in a semi-dormant condition during the growing season to conserve resources. These have showy petals that help the plant to attract insects for pollination. Beginning in mid-summer, they add a beautiful splash of color to the prairie. Typical is prairie dock, a sunflower with thick, leathery leaves that feel like sandpaper. The rough stalk grows up to 8 feet tall and is topped by a cluster of yellow flowers. The fragrant sap from this plant was sometimes chewed as gum by the early settlers.

My fall prairie garden does not contain prairie dock but has other sunflowers, asters, wild quinine, blazing star, and goldenrod. They all are weathering this dry spell with no noticeable problems, as are the native insects and other creatures that call that garden their home. Soon it will rain again, but these plants will survive in any case.

September 13, 2005

It never seems to fail that when I write about the scarcity or abundance of a particular creature, the following weeks prove me wrong. It happened again this month when I bemoaned the lack of dragonflies here at the farm. The very next day we had a green darner invade our living room, and this week, scores of the colorful insects wheeled and circled in the field across from the house.

A variety of characteristics separates dragonflies from the rest of the insect world and makes them perfectly designed for their airborne life. First of all, muscles are attached directly to their four large wings, allowing each to move independently. They can hover, fly backwards, sideways, and forward at speeds of up to 35 m/h and can stop in an instant. No other insect devotes such a large portion of its body weight to flight, as the wing muscles of a dragonfly account for 24% of its body weight, compared to 13% for the honeybee.

The head is suspended on the pointed tip of the thorax, held upright by gravity and acting as a gyroscope to tell the dragonfly which way is up. Sensory hairs inform the insect if its body tips from its horizontal position, and wing movements bring the body back into alignment. The dragonfly's large compound eyes take up two-thirds of its head and each consists of about 30,000 tiny facets that detect the slightest movement of predator or prey. Its spiny legs form a basket in which it can cradle its catch, and because the legs are directly under the mouth, the dragonfly can pass any catch to its mouth and eat while still on the wing.

Most female dragonflies lay their eggs by dragging their abdomens over the surface of a pond, releasing eggs like a bomber, although some types insert them into rotting wood or reeds at the pond's edge. Eggs may hatch within a few weeks, or may overwinter, depending upon the species. Larvae may mature and produce eggs in a single summer in some warmer areas or they may take up to five years to reach adulthood in cold water where food is hard to obtain. The larvae pass through some fifteen stages before reaching adulthood, shedding their skins and growing each time. They are camouflaged in shades of green and brown and may sit and wait for their prey to pass by, or actively stalk it. Each possesses an extendible appendage that normally is folded beneath the chin, but when the prey spotted, it shoots out at lightening speed and grasps the victim, drawing it back into the mouth.

Unlike butterflies, beetles and flies that experience a pupal stage before reaching adulthood, dragonflies have no resting period, and the adult form develops inside the exoskeleton of the last larval stage. When the development is complete, the larva climbs onto a plant or stone near the water's edge. Its skin splits down the back and the new adult dragonfly slowly extracts itself. Fluid is pumped into the wing veins to expand the wings as with butterflies and moths, and the insect then hangs and rests while the wings dry.

Adults often leave the pond area for a week or two after hatching to take advantage of insect populations elsewhere, but when they are ready to breed, they return to wetland areas. Males select and defend a territory that will attract females and there are often spectacular aerial races and battles between rivals. Even if they escape predators, adult dragonflies do not usually live much longer than two months.

A notable exception to that statement is the green darner, one of the largest, most conspicuous of the dragonflies, with a wingspan of up to 5 inches. Two different populations of green darners live in Canada and the U.S. There is a resident population whose nymphs spend the winter beneath the ice and emerge as adults in the spring, and a migratory population that arrives from southern regions each spring to breed in the north and whose offspring migrate south during August and September. Sometimes these flights involve hundreds of thousands of dragonflies, and it is interesting that some birds, particularly the smaller hawks and falcons migrate along the same paths at the same time, using these abundant insects as a major food source.

Another interesting observation about the green darner has been published by Dave McShaffrey, an Ohio biologist from Marietta College. He reported that when warm, the darner's tail was blue, but when cooled, it turned a dark purplish color, a change brought about by the movement of light-scattering sacs within the cells under the insect's skin. He suggested that the purple color might act as camouflage when the insect was too cold to fly, but as it warmed, it needed the bright blue to help it attract a mate. Watch for these fascinating insects as they move south this month.

September 6, 2005

Corn once grew on our hilly farm, but now the fields lie untilled and fallow. Still, they are far from barren. Turkeys nest, sheltered in clumps of blackberry; deer browse on the grasses and other plants; raccoons, skunks, and opossums waddle through, hunting for mice and other creatures that abound; field sparrows sing from tall milkweed stems; coyotes range down the trails that criss-cross the centers; and goldenrod turns each area into a field of gold. We consider one common species, the Canada goldenrod, a weed in our wild garden as it grows too vigorously, putting out numerous rhizomes that spread underground in all directions to form dense colonies, and there is even some evidence that it inhibits the growth of other plants by producing harmful chemicals. Nevertheless, on unfarmed fields and roadsides, this robust native is a beautiful sight.

Goldenrod flowers are tiny, but grow in numerous small clusters along their stems, so that many form large feathery sprays. Most stand about three to four feet tall but at least one grows to six feet. Some have pleasant odors. About 90 species are found in North America and our area is home to dozens. I read that the various types hybridize freely, so nobody knows exactly how many there are.

The flowers of various species of goldenrods have been used to make very popular home dyes, and the leaves, especially the aromatic ones, were used for tea by Native Americans and European settlers alike. Medicinal extracts made from such species as fragrant or anise-scented goldenrod were exported in the 19th Century to China, where they commanded high prices. Ancient diviners believed the plant could be used to find underground sources of water, and even veins of silver and gold. Many species have been moved to the gardens of England and Europe, and if goldenrod were not so plentiful, perhaps we would prize it more.

Many goldenrods have swollen lumps on their stems called galls that are the homes of two different types of insects. The round ones are home to the larval stage of the goldenrod stem gallfly. Newly-hatched larvae burrow into the stems where they hollow out little chambers and cause the plants to form swellings that shelter and feed them as well. The immature insects over-winter in relative safety, although many are still eaten by birds and other insects (and collected by fishermen, as well). The following spring, those that survive eat tunnels to the outside for later escape, and then reenter their chambers to pupate. The emerging adults then crawl out of the holes and the process begins again. There are also oblong galls that are home to moth larvae. Their adults emerge in late summer, mate and lay eggs in the foliage near the base of the plant. The larvae over-winter in the soil and burrow into the stems of the new growth, causing additional galls.

Goldenrods are extremely important to other wildlife. Bees, wasps, butterflies, moths, and flies visit for nectar and pollen. Caterpillars, aphids, and other small insects feed on the leaves and stems. The yellow and black goldenrod soldier beetles are frequently seen mating there. Then too, other wasps, spiders, lacewings, ambush bugs, beetles, and birds prey on the insects the goldenrod attracts. There is even one yellow spider, that is never found on any other plant.

Goldenrod has often been blamed for allergies, probably because it blooms in such great numbers at the height of the hay fever season. However, it has brightly colored flowers to attract insects and its pollen grains are relatively large and sticky because they are designed to be carried off by the visitors. On the other hand, ragweed flowers manufacture tiny, dry pollen that is perfect for wind transport. A single ragweed plant can generate a million grains of pollen per day and samples have been collected 400 miles out at sea and 2 miles high in the air. These pollen grains carry many different proteins on their coats that are needed by a flower to identify usable grains for its pollination. When pollen enter a person's nose or contact eye membranes, these proteins are released to the mucous membranes and exposed to the immune system where "foreign" proteins are usually dealt with. However, for some people, this does not happen, and instead, the immune system produces a class of antibodies which cause specialized cells to release histamine, a chemical which is responsible for producing swelling, redness, and itching. Some pollen types carry proteins that are more allergenic than others; for example, pine is a prolific pollen producer, but very few people are allergic to its pollen proteins, while many are very sensitive to the proteins of ragweed.

Although many of our common "weeds" originally came from overseas, the ragweeds are native. There are three species in Wisconsin, two annuals, the giant and the common, and a perennial variety. Because they do not need insects, ragweed flowers do not have to be attractive and are an inconspicuous green color. Their enormous crops of seeds are rich in oil, and provide food for small mammals and many birds, including goldfinches, song sparrows, and juncos, especially during the winter months as the seeds stay on the plants into the winter and are held high above any snow. So they are not all bad.

They also found that not all males of that species have horns, and it turns out that horn presence and size is not an inherited trait but depends upon the food a particular larva eats. If conditions are poor and the dung is low on nutrition, a larva will only grow so big and then will transform into a small hornless adult, but the more nutritious the dung ball, the larger a larva will grow. Only after it reaches a certain size will a hormone be produced that stimulates horn growth, and the more hormone in the larva, the bigger the adult beetle and larger its horns.

The scientists also extracted DNA from 48 other similar species and concluded that all horned beetles had a common ancestor with a single small horn, and that new generations tended to grow bigger horns on new parts of their bodies. They also noted that developing horns seemed to cause other features to become less prominent. Beetles with the largest horns often had smaller eyes and antennae, presumably making it more difficult for them to find mates and food. On the other hand, the researchers thought that horn size might also limit wing size, so that smaller beetles should have proportionately larger wings, but were puzzled to find no such relationship. You can see the interesting dilemmas that are present in these various observations, and why these beetles have proved such fertile ground for investigation. Next week we will look at a couple more incredible insects that may be living in your neighborhood.