Cirque de Squirrel

It's a good thing you know what squirrels look like, because I don't have a picture of a squirrel for you!  I wanted to write about them this week, but when I went to take pictures, they were gone for the day.  That's OK, though, because there is plenty of squirrel evidence visible in our outdoor classroom.  If you visit and don't see actual squirrels, look for clues instead.

Squirrels are messy eaters.  They unwrap their food, eat what's inside, then drop their food wrappers all over the place.  If you walk around the outdoor classroom and look down at the ground, you can see their food wrappers (complete with squirrel teeth marks) all over the place!  (You may notice that humans are also sometimes messy eaters - I picked up several human food wrappers out there this week.  Somehow human food wrappers are less adorable than squirrel-chewed walnut shells.)

Evidence of squirrels.

Another visible sign of squirrel activity is squirrel nests.  If you look to the top of the magnolia tree in the front yard of the beautiful building next to our classroom, you can see a squirrel nest.  Do you see it in the picture below?

Can you see the squirrel nest in the top of this tree?

Here is the squirrel nest a little closer:

Squirrel nest in the top of a magnolia tree.

Squirrels are probably the easiest topic for me to make interesting, because just about everything squirrels do is either hilarious, cute or annoying.  Here are a few fun things you might notice about them this time of year if you stop to watch them for a while.

1. Acrobatics.  Squirrels climb up and down all sorts of surfaces.  They are the only mammals that can climb down trees face-first, which they do by turning their back feet around as they descend.  Squirrels chase each other on mad dashes through the tree tops, often making great leaps from one tree to another like circus performers on a trapeze.  They also have a great high-wire act - squirrels commonly run across electric and telephone wires as easily as we run on sidewalks. 

2. Nest design.  Squirrels make extremely well-insulated nests in crevices in buildings or trees or constructed in tree branches or on top of bird nests.  They layer their nests with feathers or thistle or dandelion down (those feathery parts of the seeds).  When their nests are made of leaves, they can add layer after layer of leaves to make a hollow ball for sleeping.  The layers of leaves keep the rain out and the heat in.  Since squirrels don't hibernate, they need to keep their body temperature warm all winter, so their nests are important for keeping them warm at night, just like your nest, er, I mean, bed.  Look for squirrels carrying leaves or other materials to build nests next time you see one.  (You can try out a leaf nest for yourself.  If you layer about 50 tightly-packed leaves carefully over a balled-up paper towel then sprinkle water over the top, the paper towel is unlikely to get wet.)

3. Variety of Behaviors.  Squirrels are generalist feeders.  We always think of them as eating only nuts, but they also eat tree bark, berries and seeds.  Generalist feeders tend to have a much wider variety of behaviors than animals that eat only one thing.  Generalists must be curious about new food sources and adapt their food searching to a variety of challenges, which means their brains must be flexible and able to improvise.  Nothing against cows, but compare the variety of behaviors of squirrels to cows, and you can see what I mean.  Try making a list of all the things a squirrel does next time you see one.  I'll start: chase, dig, search in the grass, make a loud alarm call, climb up bricks.....

4. Problem Solving.  If you've ever had a squirrel figure out how to access the seeds in your bird feeder at home, you have seen the evidence of squirrels' ability to solve problems.  Once they locate a food source or nest site, they will try many new strategies to succeed in their plans to eat or build a nest.  Notice how ingenious this squirrel is at getting to what he wants despite human attempts to keep him out of the bird feeder.  Squirrels are an inspiring reminder to try many different strategies to succeed at a task.

5. Memory.  Squirrels have an unusually good memory for where they leave food.  They store food for the winter in a method called scatter-hoarding.  It's the opposite of how humans store food - all in one place in the kitchen pantry.  Squirrels leave little patches of food buried or hidden in hundreds of places, and they remember where they leave the food (they don't find their stashed food by smell - they find it by memory).  Scatter-hoarding is risky because squirrels can't guard all their food at once.  However, if their food is discovered and stolen from one location, they still have hundreds of backup locations that are unlikely to be raided.  Look for squirrels burying their food - the squirrel is almost 100% likely to come back and dig up that food later in the season. 

6. Deception.  I'm not condoning lying, but it sure is amusing to watch squirrels lie!  If a squirrel knows it is being watched by another squirrel, it will not actually hide its food.  Instead, it will pretend to hide the food by digging a hole, pretending to drop in a nut, and covering up the hole.  The watching competitor squirrel will be fooled, then the squirrel will go and hide the food in private so as not to reveal the hiding place.  It is easy to verify if a squirrel has lied.  Next time you see one bury a nut, go check and see if the squirrel has actually done so or if it has fooled you too.

Why Are There Cages of Meat in the Outdoor Classroom?

Note to lower-school teachers: please read this all the way through before you decide to share it with your students!  It was tough to figure out how many details to share for your audience.

Something is rotten in the State of Tennessee, and it just so happens to be right here in our outdoor classroom!  Unfortunately (or fortunately, depending on your perspective), the chance to see this first class example of rot will only be available for another few days.

Scientists will study anything.  And when I say anything, I mean ANYTHING!  Scientists know that even the strangest research topics can lead to useful discoveries.  For example, the discovery of new rainforest organisms can help lead to the development of new medicines, a protein discovered in jellyfish helps to grow better crop plants, and learning about the internal structures of spinach can help us build better solar panels.  The strangest details in nature can help humans change the world, so scientists study nature.  All of it.  Even when studying nature involves looking at dead organisms.  And that is why high school science students have left pieces of rotting meat in our outdoor classroom.

High school students studying rotting meat.

Decomposition (AKA rotting) is nature's way of recycling nutrients.  With no decomposition, we would have no new growth.  Decomposition is a familiar process, especially this time of year when leaves are piling up and rotting (if they are not raked up and removed).  Leaves decompose and break down where they fall, and if you don't rake them up, they will be mostly broken down into soil by spring.  Decomposed leaves return their nutrients into the soil, providing the nutrients for next year's growth.  In Middle Tennessee, we tend to have great soil because leaves from our trees decompose and add to the soil every fall.

High school student documenting the decomposition process.

Animals that die also decompose, just like plants.  Their nutrients are recycled into the soil and into organisms that use dead animals for food.  We are probably not as comfortable with the thought of animals decomposing because the sight of dead plants is so much more common than the sight of dead animals.  Also, the decomposition of animals can be a little smelly at times, since animals contain substances called nitrogen and sulfur, which are not present as much in plants.  Nitrogen and sulfur can turn into odorous compounds during decomposition (also noticed in the odor of urine (for nitrogen) and rotten eggs (for sulfur)).  But never fear - the smell isn't that bad, and it won't hurt you!  Go take a look to see what organisms are nature's recyclers of dead animals.

Animal-proof cage for decomposing meat, allowing decomposition to occur.

The high school science students have built two wire mesh test chambers for studying the organisms that decompose pork meat.  The wire mesh keeps out rats and vultures that might eat the meat before it can decompose.  The students placed the meat in the outdoor classroom last week, and they are now checking the meat daily and documenting what organisms they see on the meat (and you thought your homework was difficult!).  The teacher for their class tells me that the meat will be totally gone in a few days or up to a week and a half, depending on how warm the weather is.  The warmer the weather, the faster nature's recycling organisms will break down the meat.

Two tiny black ants summitted this mountain of meat, and beige-colored blowfly eggs coat the cut bone.

According to the high school teacher, there will be an enormous variety of organisms present on the meat over the next few days.  Mostly, there will be bacteria, which are microscopic organisms that live in and on the meat and break it down.  Bacteria will look like a white, beige or grey slime on the meat.  There will also be immature blowflies soon.  Blowflies look like metallic house flies, and they primarily lay their eggs in rotting meat.  The immature forms are called maggots, which look like fat, short, white worms.  In a day or two, you will be able to see maggots feeding on the meat (should you be so lucky).  Currently, there are a few ants on the meat.  The high school teacher tells me that ants usually show up later in the decomposition process, but I saw two ants that seem to have climbed to the top of the meat.  I thought they appeared to be very satisfied with themselves, standing on what must have been a mountain of food from their perspective!

If you wanted to investigate nature's recycling system for yourself, you could collect leaves or dead insects and monitor their decomposition in paper cups over a few weeks.  See what conditions are good for decomposition.  Is moist or dry better for rotting?  Will a dead insect decompose faster if it is sitting on moist soil or if it is alone in a dry cup?  Will dead leaves break down faster if they are open to the air or sealed into a cup with plastic wrap?  What about a leaf left whole versus a leaf torn into bits?  What leaves have decomposed more in our outdoor classroom - the ones in the pond or the ones laying around on the ground?  (See the leaf skeleton post for more on leaf decomposition.)

Why Don't Fish Need Mittens?

Brrrr!  It's been cold the last few nights!  Air temperatures dropped into the mid 20's, which is way lower than freezing.  I bundled up in many layers to survive being outside for about an hour last evening.  I felt a little bad for the fish in our outdoor classroom - they are stuck in cold water without any hats or mittens or even hot cocoa to warm them up.

A mosquitofish alive and well after several nights of freezing temperatures.

Humans are like tropical animals in terms of their thermal comfort zone.  We are comfortable living in temperatures in the 60's to 90's on the Fahrenheit scale.  We have created many devices to keep ourselves at a comfortable temperature: clothes, buildings, heat, air conditioning, insulation and ice cubes all help us maintain comfortable body temperatures whether we are in the tropics or in the Arctic.  Animals can be classified as endotherms or ectotherms, and we are of the endotherm variety.  Endotherms use some of the energy in the food they eat to keep their bodies warm.  Even though the temperature of the air inside our buildings is usually around 72 degrees, our bodies stay at 98.6 degrees.  Mammals, birds and even some fish like tuna can keep their body temperature warm using energy from food.

Mosquitofish are happy as clams in a much broader range of temperatures than we can stand.  They can live in the very warm water of shallow sunny pools in the summer, and they can survive a fairly cold winter too.  Mosquitofish are ectotherms, like most fish, amphibians, reptiles, insects and mollusks.  They don't keep their body temperature warm - they let it cool off when the environment cools off.  And as the temperature drops, they simply slow down.  Their bodies move more slowly, they eat less food, and they stay more hidden.  Many ectotherms hibernate, essentially sleeping in a cold state until the weather becomes warm enough to move around again.  If you watch our mosquitofish, you will notice that they are much slower on cold days than warm days. 

Mosquitofish can't survive if the pond freezes all they way through.  Fortunately for them, water temperature usually doesn't get as low as air temperature, so the pond is going to be warmer than the air temperature, and it won't usually freeze.  Also, ponds freeze at their surface, then the ice acts as an insulator, keeping the lower layer of the pond from freezing.  So even if you see ice on our pond this winter, it is likely that the mosquitofish will be swimming slowly in the water under the surface. 

Do mosquitofish feel cold?  I don't know.  I suppose you would have to put a mosquitofish in a fish tank with a cold area and a warm area and see where it chooses to spend its time!

Here are some other ways you can see organisms responding to the temperature at the outdoor classroom this week:

It's easy to see which plants survive freezing right now.  I'll write about this more in the deep winter, but it's probably easier to see now before the dead plants blow away and decompose.  The dead leaves in the picture below didn't survive freezing.  Either their seeds will survive the winter or their roots will survive in the ground, but it will not grow again until the spring.  The plant on the left is just fine with freezing temperatures, and it will stay growing, though very slowly, through the winter.  there are lots of winter-growing plants in our classroom.

The fern on the left survived freezing, the plant on the right did not.

The honey bees are still drinking at our pond on warm days!  They must have a fairly warm location for their hive.  Bees do some temperature regulation of their hives by eating food then shaking their wings really hard inside the hive to generate heat.  Our bodies do a similar thing - they shiver to generate heat.  Bees also flap their wings to fan the hive if it gets too hot.  Even though insects are ectotherms, bees have some endotherm ability.  Neat!

Honey bees are still drinking from our pond on warmer days despite the freezing nights.

A Visit From the Psyllid Fairy

What happens when you lose a tooth?  You get a visit from the tooth fairy.  What happens when you write a blog post about hackberry leaf gall psyllids?  You get a visit from the psyllid fairy!!!

Envelope of psyllids and leaf galls - what a great surprise!

A parent of a lower school student, and an accomplished naturalist, learned about hackberry leaf gall psyllids after bajillions of them emerged from the leaf galls of the hackberries around her house.  She had saved some psyllids to identify them and brought some to my mailbox in an envelope after she saw last week's post.  Here's what was in the envelope:

Two hackberry leaves with galls and five hackberry leaf gall psyllids.

Those tiny dots in the picture above are hackberry leaf gall psyllids.  The large brown things are hackberry leaves.  I decided to have a microscope photoshoot with the psyllids, so I used a camera with a narrow lens and held it up to the eyepiece of a microscope to take the following picture:

Adult hackberry leaf gall psyllid at 20x magnification.

The psyllid in the picture above is long dead and a bit dried out, but it still looks pretty good for a dead bug.  Psyllids are true bugs, and true bugs are insects in the group called Hemiptera.  Hemipterans have mouthparts that are good for sucking plant sap, which is what psyllids are up to when they are living inside leaf galls.  You can see the mouthpart of the psyilld pointing down from the head, which is on the left side of the insect.  You can also see one of its antennae pointing to the left of the head. 

Two dried hackberry leaves, each with a leaf gall.

This time of year, the above leaves are all the evidence you'll see of hackberry psyllids.  The adult bugs have hidden away in bark or in cracks around the outside of your house.

Many thanks to the psyllid fairy for the fabulous psyllids!

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.

Nature's Crayons

I promise this is the last post on plant pigments!  It's a short one, too.  I just want to take advantage of the last of the glorious fall colors. 

The first thing I noticed at the outdoor classroom this week is that the pond has turned brown.  The brown color is from tannins in the oak leaves that have fallen into the pond.  Our pond water has basically turned into oak tea.  The mosquitofish in the water don't seem to mind.  They are a very tolerant species.  High concentrations of tannins in water can alter the water chemistry, changing the types of organisms that can live in the water.  If we had fragile aquarium fish in our pond, we would want to change the water, but our organisms (fish and snails) are adapted to a wide variety of water conditions, including tannins.

Tannins from oak and maple leaves have turned the water brown.

The next thing I noticed at the classroom was leaves of every plant color you can think of.  See if you can name the pigments in the leaves from our classroom.  Here's a reminder of the plant pigments:

• Chlorophyll = green
• Tannins = brown
• Carotene = orange
• Xanthophyll = yellow
• Anthocyanins = red and purple

Xanthophyll in a maple leaf.

Tannins in a maple leaf.

Chlorophyll in magnolia leaves, xanthophyll in the leaf petioles.

Anthocyanins in sourwood leaves.

Chlorophyll and anthocyanins in oak leaf hydrangea leaves.

Anthocyanins, carotene and xanthophyll.

Anthocyanins, carotene and xanthophyll.

These pictures are just the tip of the iceberg.  When you walk through the outdoor classroom this week, see how many differently-colored leaves you can find.  Bring your fall Crayons if you like, and draw what you see.

Winter, Spring, Summer, Abscission

It's happening everywhere right now!  Plants are chopping off their own organs, and they are piling up in yards all over town!  How come no one is worried about this epidemic of leaf death??!!  Well, it happens every year, so I'm pretty sure the plants are going to recover.  Still, why on earth would plants get rid of their most important organs?  That's what we'll address in today's post.

Closeup of leaf abscission zone on sourwood.

In the picture above, you can see the color difference between the pale pink of a leaf petiole (technical term for a leaf stem), and the bright red of a sourwood twig.  The line between those two differently-colored plant parts is called the abscission (ab-SIZH-uhn) zone. 

Fresh leaf scar where the abscission zone dissolved and the leaf fell off.

This time of year, the layers of abscission zones are changing.  One layer is hardening and filling up with a corky substance called suberin.  Suberin is waterproof and heals what would otherwise be a wound where the leaf falls off.  The leaf scar in the picture above is dry and not losing sap because suberin has sealed the wound.  The second layer in the abscission zone is made of thin-walled, weak cells that self-dissolve when the plant is ready to shed its leaves.  Abscission zones are usually quite noticeable this time of year on any plant that is in the process of losing its leaves.  Take a look at the next two pictures and find the abscission zones.

Sourwood leaves and petioles (stems) about to undergo abscission.

The abscission zone is at the base of the leaf petiole where it attaches to the twig.

It is extremely unusual for living organisms to shed any part of themselves except for the production of offspring.  Some lizards have tails that fall off to distract predators, and many plants lose their leaves in the fall - but I can't think of other examples of falling-off body parts.  Of course, most organisms constantly rebuild their outer-coverings and some organisms can replace body parts that are bitten off, but voluntary amputation is strange, indeed! 

The loss of body parts comes at a huge cost.  Plants work all summer to catch enough sunlight to grow more leaves and get bigger, and leaf abscission every fall would seem to waste that energy.   But as with the lizards that lose their tails, there are also benefits.  Lizards' bodies escape to live another day and regrow another tail.  Plants benefit from shedding leaves by not having to maintain those leaves during the winter.  Leaves are tender tissues that would become disfigured and die when frozen.  Try putting some lettuce leaves in the freezer over night and then take them out to thaw.  You will notice they turn to mush when they return to room temperature.  In order for plants' leaves to survive winter, they would have to be tough, like holly, magnolia or spruce leaves, which take much more energy to produce.  Plants with leaves that survive freezing grow more slowly than ones that shed their leaves.

Dogwood with remnants of chlorophyll along veins and lots of anthocycanins (red pigment).

Plants have many ways to minimize the costs of losing their leaves.  They move all available nutrients out of their leaves and down into their roots to save the food for the next growing season.  Leaves fall near the plant that grew them and decompose, releasing their nutrients into the soil and further increasing the amount of nutrients recovered by the plant.  In this way, deciduous plants grow their own mulch.  Some plants, like walnut trees, even deposit compounds in their leaves that suppress the growth of competitor plants as the leaves decompose throughout the winter and spring. 

Rainbow of fall colors.

As leaves senesce (slow down and die) in the fall, they turn the variety of amazing colors we are so familiar with.  Plants' normal color is green, due to the most important compound in the world: chlorophyll.  Chlorophyll is the substance in plants that allows them to absorb sunlight and use the energy from sun to make food, a process called photosynthesis.  In the fall, chlorophyll breaks down, revealing other colorful substances plants use for photosynthesis: xanthophyll (ZAN-tho-fill), a yellow pigment, and carotene (CARE-oh-teen), an orange pigment.  As temperatures drop, some plants make anthocyanin (AN-tho-SIGH-uh-nin), a red pigment that helps the plants store sugars for winter.  Some plants reveal tanins (TAN-ins) in their leaves in the fall.  Tannins are brown in color and are thought to be waste molecules produced by plants.  They have a bitter flavor, though some tannins are pleasant, including the ones found in tea leaves.

Leaf scar on a buckeye showing scars where the leaf veins were sealed off with suberin.

So leaf abscission is a trade-off that works in parts of the world with four seasons.  Plants in the tropics and plants in colder regions keep their leaves.  Tropical plants don't have to deal with cold, so they don't shed their leaves unless there is a yearly dry season.  Plants nearer the poles of the planet don't have a long-enough growing season to start from scratch every year, so they have to grow slowly and produce evergreen leaves and needles.  We lucked out, and we get to see the beautiful fall colors that accompany leaf abscission.

Weeds: The Superhero Gang of the Plant World

The lawn in our outdoor classroom is lush, thick and inviting.  It looks like a perfect sea of even, green grass.  Just look at it!  If you stop and really look, though, you'll start to see weeds.  They are stealthy and hidden, but they are everywhere!

A clover plant thriving in a nutrient-depleted patch.

Weeds, by definition, are plants that humans consider to be growing in the wrong place.  They annoy us in our lawns, we spend time removing them from our gardens, and when they grow amongst our crop plants, they reduce the amount of food that is produced, so they cost us food, time and money.

Still, I rather admire weeds.  If you look at them from the plants' perspective, weeds are the ones that manage to survive even after people have done everything they can to get rid of them.  To make our outdoor classroom, humans removed all the vegetation and reseeded with very thick grass to completely out-compete the weeds for sunlight and nutrients, but the weeds found a way.

Spring cress, false-strawberry and a dandelion battling their way into our lawn.

Weeds usually have some unique 'special power' (well, growing ability) that lets them grow in hostile habitats.  Some weeds, like the spring cress in the picture above, can grow when it's too cold for other plants, so they take off while the grass pauses for winter (plus they have exploding seed pods!).  Clover's super power is to produce a nutrient called nitrogen that other plants can't make, so it can grow in nutrient-depleted habitats.  Dandelions, are shape-shifters: generalists that can adapt to just about any condition (plus their seeds fly on the wind).   The spurge's power (seen below) is speed: the ability to grow and make seeds so fast they can live their lives before people notice them and kill them.

A spurge weed with milky sap - tear the stems and notice it oozes a white liquid.

Some conditions are too harsh even for weeds.  Notice the worn pathways in the grass where students walk.  There don't seem to be any grass plants or weed plants there.  Now we just need to find a weed whose special powers are to grow despite dozens of people walking on them every day!

Another reason I admire weeds is that they provide variety to the types of habitats available for other organisms.  The more types of plants that grow in an area, then the more types of insects and birds and mammals and other species you can have.  Variety of types of living organisms is called biodiversity.  A pure, uniform lawn is like a desert in terms of biodiversity, because it only has one type of organism.  Weeds increase the biodiversity of our outdoor classroom.

Do you think weeds are more likely to be found in the middle of the lawn or at the edges of it?  You can experiment to find the answer.  Use a small hula hoop as your measuring device.  Throw the hula hoop randomly onto the grass in the center of the lawn and count how many weeds are present in the circle.  Then randomly toss the hoop on the grass at the edge and count weeds again.  Do this a couple more times, and you should have your answer.  Now you just have to figure out an explanation for why you think weeds prefer one habitat over the other.

Busy Fall Ants

Edward O. Wilson is one of my scientist heroes, and he has studied ants for most of the 83 years of his life.  As a child, he loved to go outside and observe ants for hours because they exhibit such a variety of behaviors.  E. O. Wilson eventually became the world's leading myrmecologist (ant expert), as well as an expert on ecology, animal behavior and conservation biology.  Thanks to him, I know some really amazing things about ant behavior, and I always think of him when I observe ants.

A foraging ant.

The ants at our outdoor classroom are busy, busy, busy this time of year.  Frost is coming soon, and the ants are foraging for their last bits of food to help get them through the cold weather coming our way.  If you stop and observe the rocks around the pond, you will start to see some patterns in the ants' behaviors as the ants bustle around in a mad rush to get ready for winter.  Below are some patterns in ant behavior that I observed.

An ant and her shadow.

The ant above was exploring to find food, also known as foraging.  Any ant exploring on its own in a zig-zag or random fashion is most likely foraging for food.  When the ant finds food, it will pick up the food and bring its food back to the ant's nest to share with the other ants in its colony.  If there is more food than it can carry, the ant will do something incredible.  It will leave a scent trail on its return to the nest to signal to its nest mates to go and get the rest of the food!  How amazing that these tiny creatures can communicate such complex information to each other.

Ants following a scent trail.

Ants are social insects that live in colonies.  The ants in a row in the picture above are interacting as a social group by following a common scent trail.  Either they are all going to get food or they are moving their colony.  Ants usually maintain a nest in a space in or near the ground.  The nest stores their food and eggs.  The ants in the picture above are all sisters!  I know this because all worker ants are female and are sisters.  The sisters work together to keep the colony alive and take care of their mom, the queen.  The queen stays in the ants nest and lays eggs.  If you look closely at a line of ants, you might be able to see if they are carrying bits of food or eggs.  If they are carrying ant eggs, they are moving the colony.  There is a colony of ants outside my back door that moves its nest every time it rains: from under the flower pot in dry weather to under a loose brick when it's rainy.  They never seem to get tired of carrying eggs around.

Ants deciding if they are friends or enemies.

If you observe a line of ants, you will probably notice ants are going in both directions, like in the picture above.  That means the ants run into each other.  Every time an ant runs into another ant, it needs to determine if the other ant is a friend or an enemy.  Enemy ants must be run off the territory or killed and eaten, and friendly ants must be allowed to pass.  Ants don't recognize each others' faces; rather, they smell each other with their antennae.  It takes just a flash for the ants to touch antennae, recognize each other, then head on their way. 

Ants are extremely important creatures on Earth.  They live in the soil and on trees and other plants, and they help recycle nutrients in ecosystems.  Ants build soil, eat pest organisms, and provide food for other insects and for birds.  Some plants are pollinated by ants, and some seeds are dispersed by them too.  E. O. Wilson has estimated that ants account for about the same amount of mass on Earth as humans do! I wonder which has had a greater impact on our planet.  I know humans have built cities and houses and reshaped the ecosystems, but ants have built the soil that all other terrestrial ecosystems are built on.

How to Read Bark Scars in Sourwood Trees

Sourwood trees are among the first to turn colors in the Fall.

The sourwood trees in our outdoor classroom are the first to put on their fall colors for the season.  Sourwoods are wonderful, smallish trees with beautiful foliage and interesting bark.  They are named for the sour taste of their leaves, which you can experience if you touch a bit of torn leaf to your tongue.  The leaves contain oxalic acid, which tastes pleasantly sour (all acids taste sour).  Tasting the leaf is not harmful, but the leaves are not considered edible and shouldn't be eaten.

The small orange-leaved tree in the picture is one of our sourwoods.

We have two sourwood trees.  Above you can see the location of one sourwood - it's the orange-leaved small tree in the center of the picture.  See if you can find the second sourwood tree when you visit the classroom.

Lenticels in young bark of the sourwood tree.

Sourwood bark is wonderful - it has so many visible features that give clues to what the tree is doing and what it has gone through during the tree's life.  A lot of people think tree bark is a dead part of the tree, but the opposite is true: tree bark is a living, important tree tissue that changes as trees grow.  Bark is mostly responsible for moving sugars (a tree's food, made from photosynthesis) between the leaves and roots.  Bark is filled with phloem tubes for transporting the sugar.  The above picture of a young twig contains tiny spots called lenticels.  Lenticels are tiny holes in the bark to allow air to get into and out of the inner tissues of the twig.  Compare the above twig to the one below.

Sourwood twig with cicada damage.

The twig in the picture above is about the same age as the one in the previous picture, but something looks wrong!  This giant gash in the bark is the healed wound cut into the bark by one of last year's cicadas.  Cicadas cut into young bark and lay their eggs in the gash where the developing offspring can feed on tree sap.  The living bark responds by slowly growing a scar to heal the wound and seal off the wood, which is what you see above.  

Older twig with young bark splitting as the twig grows larger.

Bark naturally stretches and tears and re-heals to allow tree twigs and trunks to increase in girth.  The twig above shows the first tears in young bark as the twig is getting thicker through the years.  The stretch marks get bigger as the tree gets bigger, and large branches and trunks might have deep furrows in the bark.

Scar from where a branch broke off the tree.

When branches fall off or are broken off, the bark around the broken area swells up and heals over the scar.  The scar above looks like a pretty big scar, so I suspect the branch that used to grow here was torn off unevenly.  Notice the larger tears in the normal bark above and below the branch scar.

Large gash in bark that is healing over - possibly damage from planting the tree.

Here is an even bigger scar from some major damage to the trunk.  Something cut into the bark of this tree.  Perhaps it was damaged as it was being transported or planted here.  Such an injury can weaken or kill a tree, because it can let diseases into the tree, just like a wound in our skin can become infected.  I wish more people realized this so they wouldn't carve their initials into trees' bark.  Nevertheless, this tree appears to be healing from its damage.  You can see exposed wood through the gash in this bark.  If the wound to this tree were to have cut through the bark all the way around the tree, the tree would have died, since the bark would be unable to move sugars up and down the tree.  Plant managers who need to kill trees use this technique - it's called girdling a tree.

Check out the bark on our sourwood trees and look for lenticels, branch scars, normal tears in the bark, and possible injuries to the bark.  Then take a look at other types of trees and see if you can read the scars in the bark.  Can you tell where branches used to be?  Can you see how the bark split at the tree got bigger?

Click to zoom in and see how the leaf veins connect.

When you check out the bark on our sourwoods, be sure to look at the leaves too.  Sourwood leaf veins are large, and it's easy to see the network of how the veins connect.  Also be sure to look for the remnants of flowers, now turning into fruits, at the ends of some of the branches. 

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.