No two rainbows exactly alike

Raining one minute and sunny the next, the ever changing weather of spring creates prime rainbow viewing opportunities. Just as no two snowflakes are alike, no two rainbows are alike. Rainbows can be bright, dim, a half-circle, a small sliver or be flanked by a secondary rainbow. 

Rainbows can be a small sliver under a storm cloud

The brightest rainbows occur when there are large water droplets, often during thunderstorms or heavy rainfalls. Red, green and violet shine the brightest in these rainbows. 

Rainbows with a weak red color indicate smaller water droplets and in a fine mist, only the color violet may be visible.  

Rainbows are an optical phenomenon created by sunlight and water droplets, visible only to those in certain locations. Rainbows form by light refracting and reflecting inside water droplets. 

Sunlight, while it appears white, can be separated into a spectrum of different colors: red, orange, yellow, green, blue, indigo and violet. The spectrum appears when the sunlight is refracted (bent), such as through a prism or water droplet. 

Rainbows can be very close to the horizon

Rain on gray, dreary days doesn’t produce rainbows because a key element is lacking--sunlight. Sunlight and water droplets are the two key components of a rainbow. The third is the viewer. 

To see a rainbow, the viewer has to be facing away from the sun and facing towards a rain shower (or waterfall with mist). A rainbow is visible because the sun’s rays of light are being reflected (just like an image in a mirror) inside the water droplets of the rain shower back towards your eyes. 

If the sun is too high, the rainbow will be below the horizon and you won’t see it. Rainbows are only visible when the sun is low in the sky (morning and evening) for this reason. However, when in an airplane, it is possible to see the entire circle of a rainbow.

For a primary rainbow (the main rainbow), the sunlight entering the water droplet is bent and separated into the spectrum of colors. The individual colors then reflect off the back of the raindrop and bend a second time when the light exits the front of the raindrop. Each color refracts and reflects at a certain angle, which is why the color spectrum is always in the same order (red, orange, yellow, green, blue, indigo and violet). 

Additional colors beneath the violet of a primary rainbow are called supernumerary bows

From the millions of raindrops that create a rainbow, your eye only registers one color from each raindrop. As the colors leave a raindrop, only one color will be at the right angle to intercept your eye. 

Since red light is bent the least, it will always appear on the outside of the primary rainbow, while violet is bent the most and will always appear on the inside of the primary rainbow. 

However, on secondary rainbows (the rainbows that appear outside of the primary rainbow) the colors are reversed, with violet on the outside and red on the inside. The reversal is because the light entering the water droplet undergoes two reflections inside the droplet before exiting. 

The second reflection also absorbs some of the light’s intensity, so the exiting light is typically at one-tenth of the intensity of the primary rainbow. The resulting rainbow is also twice as wide.

The colors on a secondary rainbow are reversed with violet on the outside

While each color has a specific angle that it typically refracts and reflects at, some light rays deviate slightly. This deviation is what causes the lighter sky beneath the primary rainbow. These deviating rays are only seen beneath the primary rainbow because they exit the water droplets at a higher angle, which reaches your eye. 

On the other hand, the sky is darker between the primary and secondary rainbows because no internally reflected rays, even deviating rays, exit at an angle received by the observer. 

Basically, every raindrop is refracting and reflecting the same colors of light across the spectrum, but only one color from each raindrop will be at the correct angle to strike your eye.

 

Two people standing two feet apart would see two different rainbows because different colored rays are striking their eyes. Thus, every rainbow is truly unique because every person sees their own personal rainbow.

Note: Published in the Bonners Ferry Herald on April 18, 2013.

Spinning a web comes naturally for spiders

Without a single lesson, a young spider can build its own web. As the spider grows, so does the size of the web. 

While every spider can produce silk, only 85 percent use silk to spin webbed traps. The two-dimensional orb web is the most recognized web but others include sheet webs, funnel webs and cobwebs.

Orb webs need at least three attachment points but more attachment points are used if possible.

All spiderwebs are made of silk but not the same type of silk. Spiders can produce up to seven different types of silk, each with a specific purpose. Different silk is used to make egg cocoons, release draglines, wrap prey, and create different parts of a web.

A separate silk gland, located inside the spider’s abdomen, produces each type of silk as a liquid. The silk is drawn out of the abdomen by a leg, breeze or the weight of the spider dropping--it is not squeezed out like toothpaste. 

The act of pulling the silk makes it solid, not by contact with air (as demonstrated by spiders that spin webs underwater). Pulling the silk changes the orientation of the fibers and solidifies it.

Dew and rain can't dissolve a spider's web because the silk is insoluble to water. However, the silk will absorb water and swell.

Silk is pulled from the spider’s abdomen through spinnerets, each one connected to a different silk gland. A spinneret resembles a shower-head with multiple tiny spigots. As the silk emerges from the spigots as extremely fine strands, they combine into a single solid thread. 

The diameter of silk is extremely small--0.00012 inches for a garden spider. The average human hair is 0.0039 inches in diameter.

A spider can use between 65 and 200 feet of silk for one web. Spiders will often roll up and eat an old web to conserve protein, as they may spin a new web everyday if the web is damaged.

The average orb web takes approximately one hour to complete. Orb webs are constructed in a very systematic manner.

Orb webs are the most commonly recognized spiderwebs

To begin constructing an orb web, a spider will release a fine silk line into the breeze and wait, as if fishing, until the line touches and adheres to a nearby object. Then the spider will tighten the line and add more strands until the bridge thread is strong enough to support the entire web. 

Then the spider makes a separate loose thread between the first two attachment points and moves to the middle of this thread. From there, the spider will attach a new thread and drop down to a lower attachment point, making a “Y” in the process. The “Y” makes the first three spokes of the web. 

From the hub (middle of the web), more spokes are added at precise angles, which are measured by the spider’s legs. The spokes of a garden spider’s web are 12 degrees apart. The bridge and spokes are made of non-sticky silk.

Once all the spokes are completed, the spider will start in the middle and add a temporary spiral outward. This spiral is a non-sticky guideline for when the spider returns to the center making a permanent, sticky spiral. 

As the spider returns to the center, it will eat the temporary thread while laying down the sticky thread in a spiral. At each spoke, the spider will dab the thread against the spoke and give it a tug so that it breaks up into a line of sticky beads. 

A spider waits in the middle of its web

The sticky spiral is terminated before the spider reaches the center, so that the spider has room to move in the middle. 

When finished, the spider will either settle in at the hub or sit nearby with a “signal thread” held by a front leg to stay in touch with the web. The signal thread enables the spider to feel the vibrations of a captured insect. 

Web-spinning spiders are in contact with silk threads virtually their entire life without a single lesson on how to make it work. 

Note: Published in the Bonners Ferry Herald on April 11, 2013.

Mourning cloak butterflies first to flutter around

Spring is full of firsts--the first robin, the first flower and the first butterfly. Not necessarily in that order though. The first butterfly is often fluttering around before the first flowers bloom or even emerge from the warming soil.

Emerging from under a piece of loose tree bark or from a crack in a rock on a warm spring day is the mourning cloak butterfly. Just as turtles bask in the sun to warm their bodies, the mourning cloak butterfly will crawl out and open its wings to the sun to warm up. 

The mourning cloak’s dark wings enable it to absorb heat from the sun’s rays on warm late winter days. 

Mourning cloak butterflies often look tattered in the spring because they are one of the few butterflies to overwinter as an adult

Mourning cloak butterflies are one of the few butterflies to overwinter as adults (anglewings also overwinter as adults). 

Like many other species in the spring, the first order of business is to find a mate. The males will perch in a sunny spot in the afternoon and wait for a receptive female. 

After mating the female will lay eggs on a twig of a host plant--willows, cottonwood, aspen, paper birch, hackberry or elm trees. Once hatched, the caterpillars will live communally in a web and feed together on the leaves of the plant. 

The caterpillars are black, covered with tiny white dots and marked with a row of large orange spots along its back. The two-inch-long caterpillar also grows several rows of black spines. 

Unlike a turtle’s shell that grows with it, a caterpillar’s skin doesn’t stretch as it grows. Thus, the caterpillar molts (sheds its skin) several times before pupating. The last molt a caterpillar undergoes produces a pupa. 

When a mourning cloak pupates, it will create a chrysalis to undergo metamorphosis. After 10 to 15 days (fewer days if warmer), an adult butterfly will emerge, typically in June or July. 

The undersides of the mourning cloak’s wings are cryptically colored. The grayish black pattern that appears like dark tree bark helps protect the butterfly from predators.

Even though the mourning cloak butterfly is one of the longest living butterflies at 10 to 11 months, it doesn’t flutter around the whole time. The butterfly enters hibernation in both the summer and winter. 

After emerging as a butterfly, the mourning cloak will feed briefly before finding a sheltered spot to estivate until autumn. Estivation is the summer equivalent of hibernation to avoid heat and the lack of moisture. 

Then in September, the mourning cloak butterfly will emerge once again to feed and store energy for winter hibernation (known as diapause in insects). Mourning cloak butterflies prefer to feed on tree sap and occasionally on rotting fruit and flowers. Tree sap is more readily available in early spring than flowers because the sap begins to rise in the trees. The sap will ooze out of damaged areas, including sapsucker holes.

Then as the day length becomes shorter the butterfly will find its winter hiding spot and produce an antifreeze that prevents it from freezing solid. 

The mourning cloak then waits in a suspended state until the first warm days of spring when it can emerge, bask in the sun and be the first butterfly in the woods.

Note: Published in the Bonners Ferry Herald on April 4, 2013.

Some deciduous trees forgo showy flowers, pollinate early

Buds are beginning to swell on some plants, such as the red twinberry, as the amount of daylight increases. Some plants will wait longer to ensure their leaves don’t endure cold spring nights. Other plants will wait to leaf out until after they have flowered. 

Not all plants have showy flowers like roses and apple trees, which flower after the leaves have emerged. 

Many of the native deciduous trees in north Idaho flower before they leaf out, such as aspens, cottonwoods, paper birch, alders and some willows. The flowers lack showy petals because they do not need to attract insects. Instead, the flowers are in the form of catkins, which are typically pendulous and are composed of a large quantity of same sex flowers. 

Willow catkins either appear before the leaves emerge or with the leaves

Male catkins release pollen before the leaves appear because they depend on the wind to disperse the pollen. Leaves would obstruct the wind and decrease the likelihood of pollen landing on a female flower.

Unlike flowers pollinated by insects, the pollen of wind-pollinated plants is very light and fluffy so even the slightest breeze can carry it away. Also, the pollen isn’t as sticky as pollen produced by insect-pollinated flowers because it doesn’t have to stick to an insect. Instead, the female stigma (where the pollen grain must land) is extremely sticky.

Wind-pollinated flowers also produce way more pollen than insect-pollinated flowers. A single birch catkin can produce more than five million grains of pollen.

On wind-pollinated plants, the male and female flowers are often located on separate plants. Cottonwood catkins are on separate trees, along with trembling aspen and willows. 

Aspen catkins forming seeds

By having male and female flowers on separate trees, it ensures cross-pollination and increases the viability of the species. Thus, it is crucial for copious amounts of pollen to be released by the male flower in order for at least one pollen grain to reach a female flower downwind.

Some trees, such as alder and birch, have both male and female flowers on the same tree. These plants are often “self-incompatible” which means that a pollen grain originating on that plant won’t germinate if it lands on a stigma of the same plant. 

Alders produce both male and female flowers on the same tree

Each plant produces a unique protein that prevents self-fertilization. This protein is also responsible for the allergic reaction and hay fever many people suffer from during spring. 

While less than 20 percent of plants are pollinated by wind, the copious amount of pollen produced makes them noticeable. Grasses and conifers are also wind-pollinated. 

As latitude and altitude increase, the number of wind-pollinated plants becomes more prevalent. Where the growing season is shorter, plants can get a jump-start on the season by flowering before the leaves emerge and insects appear.

Pussy willows are one of the first signs of spring

Despite snow on the ground, the pussy willow is one of the first to flower in late winter with its gray, fuzzy catkins. The pussy willow’s early catkins are one of the first signs of spring and the promise of more showy, colorful flowers to come.

Note: Published in the Bonners Ferry Herald on March 28, 2013.

No, you don’t have maggots in your house

Not a single fly buzzes through the house all winter and on a sunny spring day they all seem to come out of the woodwork--quite literally. Flies buzz and bounce off the inside of the windows trying to escape.

No, you don’t have maggots in your garbage that hatched into flies. The flies are probably cluster flies, blow flies or face flies. And they have been there since last fall. 

In the fall when the photoperiod (day length) becomes shorter and the temperatures cooler, the “clustering” flies gather on sun-warmed south and west sides of buildings. As night time falls, they crawl into any crack or crevice they can find. Then one day they don’t come out at all.

The flies will enter a suspended state, called diapause, similar to bears and marmots hibernating for the winter. Their metabolic activity decreases and they don’t reproduce or eat.

When the temperature increases and the photoperiod becomes longer they emerge from their resting place--often to the inside.

Distinguishing between the types of flies in your house requires a close look. 

Cluster flies are black, three-eighths to a half-inch long with short, yellow hairs on the thorax (middle region). Their wings also overlap when at rest. They are named for their tendency to cluster together in houses.

Blow flies are a metallic green, gray, blue or black color and are strong fliers. 

Face flies resemble house flies, which are gray with four dark, longitudinal stripes on top of the thorax. Face flies typically invade a house in the summer. 

All flies follow the same life cycle of eggs to maggots to pupa to adult fly. But each fly has a preferred medium for each stage. 

Blow flies tend to lay eggs in manure, pet waste or fresh carrion. The sudden presence of blow flies in your house may indicate a dead animal within the home, such as a mouse or squirrel. However, blow flies will seek shelter in homes for winter but the numbers are probably fewer.

House fly larvae feed on garbage, animal waste, compost or spilled animal feed. Adult females can lay 100 to 150 eggs at a time. 

The larvae of face flies develops in fresh cattle dung and are more common around farms and ranches. 

Cluster flies are not a “filth” fly. They don’t develop in garbage or dung, but instead are parasites of earthworms. A female adult fly will lay eggs in cracks in the soil. When the maggots emerge they will seek out and enter earthworms as parasites. Then they pupate in the soil after leaving the earthworm. They emerge from the soil as an adult fly and know which way is up because they are attracted to light. 

The attraction to light perpetuates for adults since they are attracted to lamps and bright windows in houses throughout the winter and spring. The cluster of flies in your windows and light fixtures will die if they don’t escape outside to find food or water. 

At least they aren’t there because you forgot to take out the garbage.

Note: Published in the Bonners Ferry Herald on March 21, 2013.

Rare White Raven

Ravens are black, rarely white. I'm lucky to have a white raven frequenting the field near our house.

Two ravens harassing a white raven

I didn't get a close look but the eyes don't appear red. Albino birds have red eyes and also lack any kind of pigmentation. The white raven could be leucistic, which means it has less than normal pigmentation resulting in a pale appearance.

White raven against a snowy hillside

Rare white raven

Photos copyright Laura Roady

Comets offer a glimpse of deep space

One doesn’t forget seeing a comet trail across the night sky for weeks. Many may remember Hale-Bopp visible in 1997 or Halley’s comet in 1986.

Typically, comets visible to the naked eye are seen once every five to ten years. But this year we have two chances. If clouds block the view this month, there will be another chance in November. 

Starting early in March, Comet Pan-STARRS (comets are named after the person, spacecraft or telescope that discovered them) became visible in the northern hemisphere. The comet was previously visible in the southern hemisphere. This comet has a narrow window to be seen, which is after sunset and before it goes below the western horizon. 

Illustration credit NASA

Comet ISON will be visible in November and is predicted to be brighter than comet Pan-STARRS and visible longer at night. 

A comet’s brightness depends on its composition and how close it orbits the sun. Like dirty snowballs, comets are composed of ice, dust, rock and gas. The comet’s frozen center is called a nucleus and often is only a few kilometers across. 

As a comet orbits closer to the sun, the sun’s heat causes the ice to change to gas. The closer the comet is to the sun, the faster the ice vaporizes.

The vaporized gas creates an atmosphere, called a coma, around the comet’s nucleus. The coma can be hundreds to thousands of kilometers in diameter. 

Solar wind and pressure from sunlight blows the coma materials away from the sun, forming a long tail. The tail always points away from the sun. 

Comets actually have two tails--a gas tail and a dust tail. The gas tail is the visible coma. The dust tail often is too dark to see. 

As the surface of the nucleus heats up closer to the sun, small particles of rock are released and form the dust tail.

Comet ISON is predicted to have an extremely bright tail because this may be the first time the comet has entered the inner solar system and passed closely to the sun.

Comet ISON is believed to have originated in the Oort Cloud. The Oort Cloud is 465 trillion miles away at the edge of our solar system, about one light-year away, and contains several trillion icy bodies. 

An icy body becomes a comet when it is nudged from its orbit at the edge of the solar system and falls into an eccentric orbit closer to the sun. The nudging can occur from a giant molecular cloud, stars passing nearby or tidal interactions with the Milky Way’s disc. 

Comets originating from the Oort Could are called long-period (or long-term) comets because they have orbits that are longer than 200 years. Some long-period comets may take thousands to millions of years to complete one orbit. These comets, such as comet ISON or Pan-STARRS, will only be seen once in recorded history. Hale-Bopp has a orbital period of 2,537 years. 

Comets with orbits less than 200 years are called short-period comets, such as Halley’s comet which completes an orbit about every 76 years. Many short-period comets originate in the Kuiper Belt, which is a disc-shaped region beyond the orbit of Neptune. Pluto is a member of the Kuiper Belt.

The nudge that puts an icy body into an eccentric orbit around the sun allows us to see something from deep space. Comets are considered leftovers from when the solar system was created around 4.6 billion years ago. 

If the weather cooperates, two icy bodies formed billions of years ago that have traveled trillions of miles over thousands of years will grace our night-time skies for a once-in-a-lifetime view this year. 

More information: 

Comet Pan-STARRS will be visible until March 24 just after sunset. The comet will start low on the western horizon in early March and move higher into the constellation Cassiopeia by the end of March. The comet will be visible to the naked eye and will appear as a fuzzy star with a small tail, about as bright as the stars in the Big Dipper. The comet will only be visible for short time after sunset and will become dimmer as the month progresses. Binoculars will enhance the view of this once-in-a-lifetime comet.

Note: Published in the Bonners Ferry Herald on March 14, 2013.

Who-Whoo is that calling in the dark?

A deep whoo, whoo, whoo-whooo, whooo-whooo resonates across the field as evening quickly fades away. The three to eight loud, deep hoots come from a great horned owl. February and March are the best times to listen for owls calling as it is nesting season for most of them. 

Great horned owl

Owls call to attract a mate and establish a territory. Typically larger owls make lower-pitched calls than small owls. Male owls also have  lower-pitched calls than females.

Cold nights don’t deter owls from sitting on eggs as early as February. Great horned owls have been known to successfully incubate eggs when nighttime temperatures drop down to as low as minus 27 degrees Fahrenheit. 

When owls nest, they don’t build their own nest. Instead, they take over the nest of others, such as crows, ravens or eagles, or nest in tree cavities or on rock ledges. 

An owl’s eggs indicate where the owls nests. Screech owls nest in woodpecker holes and their eggs are very round because they cannot fall out of the cavity. Whereas, barn owls have more oval eggs because they nest on ledges in barns or on rock cliffs. A round egg could easily roll off a ledge, but an oval egg rolls in a circle. 

Owls are raptors, also known as birds of prey, like hawks, falcons, eagles, osprey, vultures, condors and kites. All raptors are good hunters because of their eyes, beak, talons and wings.

Western screech-owl

Raptors have excellent eyesight, up to ten times stronger than our eyesight. If our eyes were comparable to an owl’s eyes, they would be the size of tennis balls. 

Unlike our eyes, an owl’s eyes are fixed in the socket and they only see in shades of gray. An owl’s eyes don’t move because they are packed full of rod cells. They have no cone cells which would allow them to see in color. 

The density of rod cells helps them see at night under the light of the moon and stars. They cannot see in complete darkness.

To compensate for their eyes being fixed in the sockets, an owl can rotate its head 280 degrees quite quickly. 

Barred owl with skeleton

An owl’s eyes are front-facing which leaves less room for a beak on its skull. Other raptors have side eyesight, such as eagles, and have a larger beak. A larger beak enables the raptor to crunch bones into smaller pieces to swallow.

Since an owl has a small beak, it cannot crush bones into small pieces. Therefore, an owl swallows bone in bigger pieces, which is evident in the owl pellets they regurgitate. 

Great gray owls, the largest owl in Idaho, can swallow a whole mouse. The mouse moves down to the owl’s crop, which separates the meat from the indigestible parts (bones, fur and feathers). Six to eight hours later the owl will silently cough up a pellet, the width of its throat, with the indigestible remains. 

Largest to smallest: Great gray owl, barn owl, northern saw-whet owl, northern pygmy-owl

Unlike other raptors that tear meat off the bone, owls eat the entire animal for the nutrition. They absorb calcium from the bones and other nutrients from the indigestible parts before they are regurgitated.

Like all raptors, owls use their sharp talons to capture prey, which ranges from rodents to birds to squirrels--even skunks for great horned owls. All birds have nails at the end of their toes, but raptors have very sharp, long, pointed nails that are curved, which are referred to as talons. 

All raptors also have over-sized wings to help them carry the weight of their prey, which can be as much as half of the bird’s body weight. Fast-flying raptors have narrow wings that come to a point with stiff feathers and a smooth leading edge. This configuration allows the raptor to fly fast but not quietly.

Fast-flying raptor's wing on top, owl wing on bottom

An owl’s wings are configured to fly slow and silently. Their round-ended, wide wings with soft feathers and fringe along the leading edge act as a muffler, allowing the owl to silently ambush its prey. With silent flight, the only time we will hear an owl is when they call. 

Note: Published in the Bonners Ferry Herald on March 7, 2013. 

Note: Thanks to Beth Paragamian, an IDFG wildlife education specialist, for bringing the live owls and owl mounts to KNWR for an owl program.