Hello! I'm Veronica. I'll Be Your Nectar Guide Today

The plant below is called Veronica.  That's its scientific name and its common name.  In our outdoor classroom, it's located on the rocks behind the pond, and it's blooming like crazy right now.  Veronica flowers have something really neat called nectar guides. 

Nectar Guides on Veronica Flowers

Nectar guides help bees find flowers.  They point to the part of the flower that contains the nectar, which is what bees are looking for.  Nectar is sugary plant sap found in the base of many flowers, and it is perfect bee food.  I like to think of nectar guides working a lot like the stripes and lights on airport runways telling airplane pilots where to land their planes.

Why would flowers advertise where their nectar is?  It turns out flowers are offering the nectar in a bargain.  Do you see those tiny white structures poking out of the flowers in the picture above?  Those are anthers, and they contain a dust called pollen.  Flowers must have pollen moved from one flower to another in order to be able to grow seeds to grow a new generation.  While a bee sips the nectar in a flower, those anthers are in the perfect place to dab some powdery pollen onto the bee.  Then the bee rubs off the pollen at the next flower it goes to.  The flowers are giving the bees a meal in return for moving their pollen from one place to another.  (Do you remember the name for a close relationship between two organisms where both organisms benefit?  The answer is at the bottom of this page.)

Bee-pollinated flowers usually have nectar guides.  Flowers that are small, fragrant and with a shallow cup for nectar are usually bee-pollinated, and we have lots of bee-pollinated plants at our outdoor classroom to discover.  You may not always notice nectar guides on bee flowers because sometimes the guides are invisible to human eyes.  Strangely enough, there are more colors of light than humans can see.  Rainbows actually have more stripes than humans see, in colors we haven't imagined.  Bees can probably see one more stripe on the rainbow than we can.  We call this color ultraviolet, and know it exists because we can detect ultraviolet with machines.  But how do we know bees can see ultraviolet?  Because scientists have given bees eye tests!  Scientists tested bees' eyesight by making fake flowers.  On some flowers, they painted nectar guides with an ultraviolet dye.  When you offer fake flowers to bees, the bees are way more curious about the ones with the ultraviolet nectar guides than the ones without nectar guides.  Scientists have detected ultraviolet nectar guides on real flowers (sunflowers have ultraviolet nectar guides).

Go back to the picture above and see if you can find the nectar thief.  A nectar thief is something that steals nectar without moving pollen - a parasite!  The nectar thief on our Veronica flowers is an ant toward the left of the picture.  As we learned last week, ants eat sugar, so it's no surprise that they would like flower nectar.  The ants are too small for the anthers to dust them with pollen, so they slip in, drink the nectar and slip out again without helping the plant.  Ants mostly use smell and taste to find their way in the world, so they probably don't even notice the nectar guides.  If you are jealous of bees for seeing one more color than we do, then you're really going to be mad at ants.  Scientists think ants can smell and taste an enormous number of things humans can't, with much more precision.  If you don't believe me, try closing your eyes and finding your way around using just your nose and tongue, and you will appreciate just how much better ants' senses are.

Answer: Mutualism

Down on the Aphid Ranch

Originally this post was just going to be about vines.  There are four basic plant forms: trees, shrubs (small, branched trees), herbs (non-woody, soft plants), and vines.  Vines are woody but not strong, and they grow as tall as trees by climbing up other structures, often trees, and they usually have roots that are good for holding on, like this:

English ivy with roots that are good for holding on to buildings or trees.

 Some vines are evergreen like the English ivy on the back wall of our classroom:

English ivy doesn't lose its leaves in winter.

And some are deciduous like the milkweed vine on the lamppost by the playground:

Milkweed vines lose their leaves in winter.

Like I said, I was originally going to post about vines.  BUT when I was looking through my vine pictures, I noticed a very lucky but accidental detail on this picture of the English ivy:

New growth on the English ivy with some curious dots on the stem.

Look very closely at the stem, and you will notice there are ants walking on that stem:

Ants going up and down the ivy stem.

I started to wonder what ants were doing walking on an ivy stem, since there is not likely to be much ant food at the top of an ivy vine.  Then I looked even closer and I saw this:

An farmer ant and her aphids.

Now we have a story!!!  The picture is a little blurry, which means you're going to have to go out to the outdoor classroom and see this for yourselves.  The dark spots are insects called aphids (which can also be whitish or greenish), and the reddish brown spot is an ant.  What the ant is doing is called aphid farming.  It's a bit gross, but it's so amazing that it's completely worth learning about.

To explain aphid farming, we have to go back to plant sap.  Remember plants do photosynthesis and make sugars, which are dissolved in plant sap, making plant sap slightly sweet?  Aphids have pointy, needle-shaped mouthparts they poke into soft plant tissues, and they suck the plant sap out of plants for their own food - much like the psyllids we learned about back in the fall.  Since aphids live closely with plants, they are said to be in a relationship called a symbiosis.  In this relationship, the aphids are harmful to the plants because they 'sap' their energy.  The aphids benefit by getting food.  A symbiosis where one organism benefits and the other is harmed is called parasitism. 

Here's where it gets slightly gross.  Aphids drink a lot of plant sap, and they digest most of the sugar in it, but not all.  The leftover sap with a tiny bit of sugar in it goes on through and out the other end of the aphids' digestive system.  In all other organisms, this substance would be called feces or poo, but in aphids, the substance is a clear and sugary liquid, so it's called honeydew.  (Do NOT confuse this kind of honeydew with the delicious green melon you find in the produce section.)  If you have ever noticed sticky, clear spots on the hood and windshield of your car if you park it under a tree in summer, you have seen the results of the mist of honeydew that rains from the aphids in the tree.  Take a deep breath...it's really only plant sap run through an aphid!

OK, here's where it gets really gross, but also really, amazingly neat.  The sugars in the honeydew are technically a food source (like any other sugar), and ants eat sugar.  Put those two facts together, and you know what that ant is doing with the aphids on the leaf in the picture above.  Yes, some ants eat honeydew.  The ants know a good food source when they find it, so they protect the aphids and fight off aphid predators.  They even move the aphids around to better sap sources if their honeydew production slows down.  Some ants even keep aphid eggs in their ant nests in the ground during winter and place them on new plant growth in the spring so the aphid eggs have food when they hatch.  The ants are said to farm the aphids - just like humans farm cattle!  Dairy cattle ranchers protect the cows and move them around to new pastures with more food.  Cattle farmers also protect calves and raise them to adults.  And cattle are farmed to provide a liquid food source: milk! 

It's amazing to me that humans are not the only type of organism that does farming.  Ants live in groups and have very complex behaviors, as exhibited by the aphid farming.  Their behaviors often mimic human behaviors: they have 'jobs', fight battles, farm aphids (and fungi - neat story for another time), build large complicated structures and much more.

Ants and aphids are in a symbiosis - they live very closely together.  Their symbiosis involves both organisms benefiting from each other.  The aphids get protection, and the ants get food.  A symbiosis where both organisms benefit is called a mutualism.  Humans and cattle are in a similar mutualism.

The new growth on our ivy is very likely to have a constant supply of aphids and ants, so you should be able to find them any time!

Mosses, Lichens and Succession

Life has a way of taking over here on Earth.  Any surface without living things on it will eventually have life growing on it if you wait around long enough.  A new sidewalk of poured cement will have plants growing through cracks after twenty years.  New roofs will eventually become soft and covered with mold, moss and even plants.  Fresh lava from a volcanic eruption will cool, harden and in several decades be covered by a forest (Neat example here).  The invasion and growth of life on nonliving surfaces is called succession, and it's happening right here in our classroom.

Green and grey lichens growing on rock.

The nonliving surfaces we have at the classroom are mostly the rocks.  The big boulders and the flat rocks around the pond are too recently dug from the ground to have life on them yet, but they probably will by the time you graduate from high school.  The rocks with the waterfall behind the pond and the rocks that make up the wall at the back of the classroom have been exposed at the Earth's surface for long enough to have some neat life growing on them. 

Organisms that can colonize bare rock are called pioneer species.  Lichens are usually the first pioneer species, and they look like color splotches on the surface of rocks - white, green, grey, yellow or even orange.  Lichens are actually two organisms for the price of one: a fungus and an alga living together.  The fungus and alga form a mutualism - an interaction where both organisms benefit.  If you remember from the beginning of the year, algae grow in our pond - algae can only live where they don't dry out.  In lichens, they live surrounded by cells of fungus so they can live outside of a pond.  In return for this good protection, the algae provide the fungus with food from doing photosynthesis.  Together, the organisms that form lichens make acids that slowly dissolve the rock on which they grow, which makes tiny crevices in the rocks.

White, green and grey lichens plus dark green mosses growing on a rock.

Once lichens have been growing on rocks for a while, mosses are able to survive there too.  Mosses are plants that don't have flowers or stems or roots - just tiny green leaf-like structures and microscopic hair-like structures.  Mosses send their hair-like structures into the crevices the lichens made in order to anchor themselves on the rock.  Then the mosses grow bigger.  They die back during harsh weather and grow more in good weather.  As they die back, their dead parts decompose in place, and they turn into a tiny bit of soil.  After several years, mosses build up enough soil underneath themselves that other plants can move in.  Mosses can also start to grow in cracks and pockets in rocks.

Just as mosses build habitat for small flowering plants, the flowering plants provide habitat and food for more creatures.  Flowering plants have roots that hold the soil in place, and they also add to the soil as they die back each winter and decompose.  Mosses and plants can host tiny insects, adding to the variety of life growing on a formerly bare rock.  As the years go on, the soil builds and builds and larger plants, shrubs and eventually trees can grow on what was once bare ground.  Eventually a mature forest might be found where once there was bare rock, and succession has been a success.

A rather large moss behind the waterfall.

Next time you are near an older neighborhood or a vacant lot in Nashville, see if you can recognize succession.  Old houses have mossy roofs.  Ancient stone walls are covered in plants with trees growing through them and lizards living between the stones and roots.  Old parking lots or yards are infiltrated with weeds and dotted with butterflies drinking from the weeds' flowers.  You can see the results of succession at the River Campus too.  Most of what is now the wetland used to be an open farm field with only grass - only 15 years ago!  Now it has grown into a young forested wetland with lots of plants and small trees.  Life certainly does take over!

Looking Over Clover

To any person who has spent enough time sitting on a patch of lawn to get a little bored, the leaf in the picture below will be instantly familiar. 

One clover leaf.

It's a leaf of the white clover plant, and there is plenty of it at out outdoor classroom right now.  One clover leaf has three parts, which is reflected in the Latin name of the plant: Trifolium repens.  Tri- means three, and folium means leaf.  Repens means reclining, which this plant does well, as it spends its entire life within about 3 inches of the ground.  Clover leaves usually have faint white lines in them, and they are never heart-shaped.  Another common lawn plant called oxalis has leaves divided into three heart shapes, and sometimes people get confused about it.

A patch of clover.  See any lucky ones?

White clover has several claims to fame.  First, they are tough little plants, and they survive well on lawns even under heavy foot traffic, so they grow everywhere there is a lawn.  People who are sticklers for uniform-looking lawns consider the plant a weed, but many people value the plant for its ability to grow in harsh conditions where grass can't grow.  Second, clovers are known and loved for their sweet-smelling flowers, which are white or pinkish clusters on stems.  I bet you have made a flower chain from clovers before.  Bees love the flowers even more than humans do, and they make great honey from it.  The sight of clover flowers on a lawn should serve as a warning to wear shoes, since bees are likely to be on the flowers, and stepping on a bee will get you stung.  Clover's third well-known benefit is its value as a food source for animals.  Clover seed is often included in the mix of seeds farmers plant for growing cattle forage (the plants cattle eat).

A small clover plant with leaves, stems and roots.

Clover also has a secret.  Most people don't know much about the hidden power that makes clover so important in nature and explains some of its better-known characteristics.  If you dig up a small clover plant and look at the roots, you see something that is not usually present on plant roots: tiny lumps.  Those lumps are called nodules, and they are actually little areas where clover keeps its own pet bacteria.  The clover provides food and housing (and maybe even affection) to the bacteria in return for the services the bacteria provides to the clover.  The bacteria produce an otherwise almost unobtainable nutrient called nitrogen.  Nitrogen is a nutrient used to make protein - the microscopic parts of organisms that provide much of their actual structure as well as much of the machinery to conduct life's processes.  Other plants can only get nitrogen by absorbing leftover nitrogen from dead clover-type plants or from decomposing animals or animal manure, but clover has its own constant supply.

Root nodules on a clover - where nitrogen is fixed.

Clover's source of nitrogen means it can grow on poor soil where grass can't.  It also means it has a high nitrogen content, making it more nutritious than grass for animals to eat.  When clovers die, they leave behind richer soil with more nitrogen, where other plants can now grow.

Clover is related to bean-type plants (pinto beans, Limas, black beans, lentils, peas), and all types of bean plants have the same pet bacteria for making nitrogen (actually called fixing nitrogen).  This type of interaction between two organisms that live in close contact and help each other is called mutualism.   Can you think of other examples of mutualisms?

Have you ever found a four-leaf clover?  Sometimes the plant makes an error when growing its leaves, resulting in our four-leaf symbol of good luck.  If you look at a patch of clover for long enough, you will probably find a four-leaf clover.  If you do, press it flat between pages of a book for a week or so, then you can glue it to paper or press it between clear tape to preserve it.

Help! I've Got Hackberry Leaf Galls!

Last week students in our outdoor classroom sent the picture below, wondering what it was.  It's a very logical question, since those...things are growing out of what is obviously a leaf, but no normal leaf has weird miniature mushroom-shapes growing out of it.

Hackberry Leaf Galls (photo: M. Sherman)

The leaf above comes from a hackberry tree, whose bark I think is fantastic, and which we will explore later in the winter.  We have a gigantic hackberry tree in the outdoor classroom, and it's at the end of the row of parking spaces near the road.  Here's our hackberry:

Hackberry tree with most leaves already gone for the winter.

If you search through the fallen leaves around the classroom, you can find lots of hackberry leaves right now.  They have toothed edges (lots of tiny points), and they narrow to a tip.  Also, the wider end of the leaf usually is lopsided with one side larger than the other.  Most of the hackberry leaves have one or more of those big lumps on the lower side of the leaf.  The lumps are called leaf galls, and they are scar tissue the tree has grown in self defense against a parasite.

Three hackberry leaves, two with galls, one without.

So, what exactly is a parasite, you ask?  A parasite is a small organism that lives on a larger organism and often uses the larger organism for food, harming the larger organism in the process.  The larger organism is called the host.  There are lots interesting types of parasites in this world.  Dogs and cats sometimes have fleas for parasites.  Deer often have ticks.  Humans can sometimes have lice.  And plants can have parasites too.  The parasite on our hackberry leaves can only live on hackberries, not humans.  It is a type of insect called a psyllid (SIL'-id).  Psyllids look just like tiny cicadas - smaller than a grain of rice.

I broke open this gall, but it was empty.  The adult has already emerged from it.

Hackberry leaf psyllids lay their eggs on the underside of hackberry leaves in the spring.  The eggs grow into immature psyllids that look like this.  The psyllids damage the leaves, which causes the leaves to grow a lump of scar tissue (a gall).  The psyllids eat hackberry sap and live inside the gall as they grow larger through the summer.  In the fall, the psyllids grow into adults and drill out of the gall.  They fly or crawl to find crevices in bark or buildings to overwinter safely.  When the weather warms up in the spring, they lay eggs and start the cycle again. 

Hackberries grow well in Middle Tennessee, yet they almost always have hackberry leaf galls damaging their leaves.  The trees don't seem overly harmed by the gall psyllids' damage.  This is normal parasite behavior.  Most parasites don't cause extensive harm to their hosts.  They take just a little food from them but not enough to kill them.  If a parasite ate too much of its host and killed it, the parasite would be out of food and would die too.  Parasites use their hosts in a sustainable manner so that their food source will be available in the future.

Tube Flowers and Their Pollinators

Butterfly bushes (Buddleja sp.) are very well-named.  The ones in our outdoor classroom are usually surrounded by several butterflies flying from flower to flower and filling their butterfly bellies with nectar.  If you look closer, you'll notice that lots of types insects like butterfly bush nectar, and even hummingbirds have been known to drink from these flowers.  Because of the shape of butterfly bush flowers, not all nectar-feeders are able to use these plants.  All butterfly-bush-feeders must have long, thin mouthparts that fit into the flowers.  Notice the long curved proboscis on the skipper in the photo below.  The proboscis works like a silly straw, curving and extending into the base of each flower for a sip of nectar.

A skipper sipping nectar on a butterfly bush.

Below you can see one individual flower of the butterfly bush.  The green bit is the base of the flower where nectar is produced.  The purple petals form a tube that opens at the top of the flower.  The tube shape does a good job of keeping out insects that steal nectar without pollinating the flower.  Insects that can reach their mouthparts into the flower receive a dusting of pollen as they sip nectar.  When the insects move to the next flower, they drop off the pollen, allowing the flower to produce seeds.  Nectar-sippers and flowers have a trade-off where each organism benefits from the arrangement: flowers are pollinated and the pollinators get food.  This relationship is called a mutualism, and it is a type of symbiosis where two organisms benefit from the interaction.

A single tube-shaped flower of the butterfly bush.

The purple tube-shaped flowers have orange centers to help insects find their way into parts of the flower where the nectar is produced.  Most flowers have nectar guides in their centers.  Usually nectar guides are yellow or orange regions with lines pointing to the center of the flower.  Next time you are at the outdoor classroom, look for nectar guides in butterfly bush flowers and any other flowers you'll see.

Yellow/orange nectar guide inside a butterfly bush flower.

Below you can see two more organisms that are mutualists with butterfly bushes: bees and longhorn beetles.  Both pollinate the flowers and get fed in the process.  There are some insects that 'cheat' the butterfly bushes out of their pollen.  Some types of caterpillars, beetles and ants chew through the base of the flower, drink the nectar, and leave without pollinating the flower.  Look carefully at our butterfly bush flowers for some crime-scene evidence:  if you see holes chewed through the base of their tubes, you know the nectar has been stolen with no pollination payment in return!

Bumblebee and longhorn beetle working the butterfly bush flowers.

Interesting side not:  The bumblebee in the photo above was not actively feeding.  It was just holding on and resting.  This time of year, the temperatures are dropping, and insects that don't overwinter are nearing the end of their lifespan.  It could be that this bee is slowing down because it is old.  Alternately, the bee could be finding its home for the night, since I took this photo in the early evening.  Bumblebees often sleep in large flowers or near small flowers so they have a food source in the morning (wouldn't you love to sleep in a flower?).  A third possibility is that the bee is just slow because the temperature is lower.  Some bees just slow down when the temperature drops, stay in a torpor through the cold winter, and then speed back up again in the summer when it's warm.