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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

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The goat's-beard "puffball" seed head is a fragile, geometrical sphere.

© Don Blegen

August 2007

Transformations

Plants and animals change form, shape and appearance as they mature through the seasons. See for yourself.

Don Blegen


A group home on hackberry
A fragile, geometric marvel
The mystery of the hovering sphinx
When plants take winged flight
Master of two worlds

Wisconsin's outdoors is filled with fascinating plants and animals. Quite often, these species are well-known and familiar to us in one stage of their life cycle but relatively unknown in another. Here's a shortcut to recognizing some of these relationships. Even after years of observing nature, it's enjoyable to see more of these connections.

A group home on hackberry

If you live near a hardwood forest, the chances are good that scattered among the maples, oaks and hickories are a few hackberry trees. Hackberries (Celtis occidentalis) are easily recognized by their warty, furrowed bark.

This tree is the host plant to the hackberry butterfly, sometimes called the hackberry emperor (Asterocampa celtis). Its caterpillar feeds only on hackberry leaves. The hatched caterpillars can be so abundant and feed so voraciously that they can strip whole areas of hackberry trees free of leaves. Usually this does not do any long-term damage. After the caterpillar goes into a chrysalis for about a week, the caterpillar emerges as a beautiful butterfly with unusual feeding habits. Unlike most butterflies, the emperor does not seek a sip of flower nectar. It has a more robust appetite for stronger flavors and feeds on rotten fruit, carrion, dung and tree sap. Hackberry butterflies drink readily out of puddles of standing water. They seem absolutely unafraid of people. In fact, they can get real familiar landing on your arm and sucking up a bead of perspiration with their uncoiled proboscis.

Hackberry butterfly caterpillars feed exclusively on hackberry leaves. © Don Blegen
Hackberry butterfly caterpillars feed exclusively on hackberry leaves.

© Don Blegen

The female butterfly lays her eggs in a clump on a hackberry leaf. Dozens of tiny caterpillars with their big appetites devour leaves right next to their nursery sites. The butterflies often raise two generations a year that hatch out in midsummer and later in the summer. If the second generation hatches too late in the season, the caterpillars can hibernate on the trees and will undergo metamorphosis the following spring.

After pupating in chrysalises, they emerge as hackberry emperor butterflies. © Don Blegen
After pupating in chrysalises, they emerge as hackberry emperor butterflies.

© Don Blegen

A fragile, geometric marvel

Yellow goat's-beard (Tragopogon pratensis) is an exotic species from the Old Country, an introduced weed from Eurasia that grows in ditches and waste places. Its blossom is nothing to get excited about, just a yellow dandelion look-alike, but what the flower becomes is something special.

Like the dandelion, the yellow goat's-beard blossom is a composite. That means the blossom is not one flower, but a compilation of many, in this case, as many as a couple hundred individual blossoms. When these flowers mature and develop into a seed head, they form a model of geometry. Each flower forms into an aggregate cluster of seeds so intricate that many people call it a "puffball," not to be confused with the fungi of the same name. The goat's-beard puffball is similar in form to a mature dandelion seed head. If picked very carefully so as not to dislodge any of the parachute seeds, goat's-beard puffballs can be used in floral arrangements.

Yellow goat's-beard has a beautiful symmetrical flower. © Don Blegen
Yellow goat's-beard has a beautiful symmetrical flower.

© Don Blegen

On close examination, the seed head has developed into an example of geometric perfection unfolding in an intricate pattern that rivals the most complex origami designs. Take a close look to appreciate it; a description in words can't do it justice.

The mystery of the hovering sphinx

The adult white-lined sphinx moth (Hyles lineata) is often mistaken for a hummingbird. It feeds on flower nectar and its darting, rapid flight looks very much like that of a summer hummer. The moth is about the same size as a hummingbird as well. Sphinx moths can hover motionless in midair, move left, then right, up, down, even backwards like a hummingbird. Its wings beat so rapidly that they blur and hum. No wonder people confuse them!

If you get close enough, you will see that the moth sucks nectar with a long tube or proboscis that coils up like a watch spring when not in use. Also look at its legs. The moth has three pair and its back is covered in tiny scales, rather than feathers.

The white-lined sphinx moth belongs to a large group of moths collectively called sphinx or hawk moths. They are all excellent fliers that have sucking tubes as long or longer than their bodies to reach deep into flowers. Most of the family grows from caterpillars that have sharp spikes or horns on their rear ends. Such caterpillars are often called "hornworms."

Many of the hawk moth caterpillars feed only on specific plant species. The white-lined sphinx moth is not so choosy. It will feed on grape, Virginia creeper, purslane, apple blossoms and other plants. It pupates on the ground forming a chrysalis with a long "handle" that contains the developing proboscis. After undergoing a complete metamorphosis inside the chrysalis, the moth changes from a wormlike caterpillar into a remarkably nimble master of flight that hovers near flowers, extends its proboscis into the center of flowers to suck up nectar, then rolls its proboscis back into a tight coil before darting on to the next blossom. Watching it perform intricate aerial acrobatics, it's hard to believe this same creature spent most of its life crawling around as an ugly green caterpillar with a spine sticking out of its south end! Truth really is sometimes stranger than fiction!

When plants take winged flight

In late March or early April, box elder trees (Acer negundo), and other members of the maples, produce blossoms that pop out even before the leaves emerge. The tiny blossoms lack the showy petals and sweet smells we usually associate with flowers. Nevertheless, these are true flowers and have all the necessary reproductive equipment to produce fruits and seeds.

The main difference is that these are wind-pollinated flowers and do not need to expend the effort to make bright colors and sweet odors that fruit trees use to attract insects to carry the pollen from one blossom to another. Wind-pollinated flowers specialize in producing huge quantities of pollen to increase the odds that a few grains will land by chance on another receptive flower. In box elders, the flowers are single-sexed coming in either the male (staminate) or female (pistillate) forms. Male flowers produce the pollen that contains the sperm and female flowers contain an egg inside an ovary. Once fertilized, the pistil undergoes a dramatic change and develops into a dry type of fruit containing a seed.

In the case of box elders and all other maples, that fruit takes the form of a samara. To kids of all ages, they are the "helicopter seeds." Actually, they develop into a double samara over the summer and greatly increase their size. Come October, the tree's leaves all fall, but the samaras hang tough. It often takes a stiff wind in November or later to split the twin samaras at their joining point and dislodge them into whirling flight.

If a seed falls directly beneath the parent tree, its chances of maturing into a new tree are close to zero because it can't get the light and nutrients it needs to grow. Seeds need to be carried outside the shadow and root-reach of its parent. The parent tree is immobile and can't distribute its progeny by moving from place to place as animals do. A winged samara is one clever way to catch the wind, whirl horizontally great distances and at times even gain altitude. On a windy day in winter, the snow may be covered with samaras that have finally spun their way free at great distances from their parent trees, guaranteeing success of another generation of box elders – pollinated by the gentle breezes of April and spread far and wide by the harsh winds of early winter.

Master of two worlds

Just about everyone knows that butterflies and moths transform from caterpillars. But another kind of flying insect, the dragonfly, makes a life change every bit as dramatic.

The dragonfly begins its life as a wingless, gill-breathing aquatic insect that can move by crawling or by jet propulsion. It finishes its life as an air-breathing aerialist, arguably the most acrobatic of all insects.

A dragonfly nymph is a fierce predator, capable of devouring other aquatic insects and even small vertebrates like tadpoles and minnows. It ambushes prey by blending in with bottom twigs and weeds or by shooting water out of its abdomen, darting at prey with amazing speed. In either case, the coup de grace is administered by a unique jaw assembly that is as deadly as that of any monster in an Alien movie. Its jaw is hinged, extensible and tipped with two forceps-like jaws that pierce and hold the victims in a viselike grip so they can be eaten.

The nymph spends up to three years living in a pond, lake or slow-moving stream. Then, on some kind of an inborn signal, it crawls out of the water into the air and climbs up a reed, a boat dock or any other vertical object near the shoreline. The nymph's back splits open and the creature within crawls out, leaving the empty case behind. This new creature crawls upward an inch or two, and the hump on its back slowly unfolds into silvery, shimmering wings. The wings are wet at first, filled with a fluid forced into them by some internal pump. Gradually, they dry as four transparent wings that are delicate-looking but possess remarkable structural strength.

In an hour or two the process is complete and the creature launches into flight. For the next several weeks or months, the adult dragonfly will rule the air until old age or frost cuts it down. Capable of speeds exceeding 40 mph, able to hover in midair, to turn so abruptly that the eye can hardly follow the movement, able even to fly backwards – the crawling nymph has been transformed into an aerobatic marvel that can pick flying insects out of the air with casual grace. It is a true mosquito hawk, devouring mosquitoes, gnats, midges, mayflies and other protein-rich flyers. Shifting, wheeling, darting, hovering, the dragonfly slices the air in sweeping arcs as its huge eyes pick up the tiniest movement in any direction, its spiked legs forming a kind of caching basket to scoop prey from the air. Its jaws crunch up one mosquito in mid-flight as the 25,000 lens facets of its two huge eyes search for and locate the next, and its powerful wings maneuver into position for the next interception.

Sometime during the summer, the female will lay her eggs. Some do so on the water's surface and the eggs sink like little stones. Others make a slit in emergent vegetation and lay their eggs in the cavity. Either way, after a short time, the eggs hatch into small nymphs with big appetites. Few survive, but the lucky ones feed fiercely and grow steadily shedding their old skins as many as 10 times before the last molt. One day, the nymph that has lurked in the dark depths for so long walks out of the only world it has known into another completely different realm to be transformed into a lithe creature of air and light, its tiny brain holding an instinctive memory of the intricacies of flight and the tactics of aerial attack.

Photographer, author and retired biology teacher Don Blegen writes from Spring Valley.