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.

All About Mosquitofish

Our pond is full of Eastern mosquitofish (scientific name Gambusia holbrooki).  They were introduced to the pond to help eat aquatic mosquito larvae in order to reduce the number of mosquitoes in our outdoor classroom.  The mosquitofish are definitely helping to limit mosquitoes, but we'll have to convince the mosquitofish to jump out of the pond and eat mosquito larvae that grow in little pockets of water in mulch, soil, tree bark and other places too.  Very soon, we will have no mosquitoes, since night-time temperatures are getting colder, and adult mosquitoes will die off for the winter.

Hello there!  A mosquitofish says 'hi' with its pectoral fin.

Mosquitofish are generalist feeders, meaning they eat all kinds of things.  They eat algae, snail eggs, mosquito larvae, other insects, and even each other!  These little fish are good survivors, since they can eat almost anything.  Interestingly, generalist feeders in the animal world tend to be more intelligent that animals that only eat one kind of thing.  Generalists' brains must be more flexible and contain more information to remember all the different kinds of things that qualify as food.

Fish are not the brightest bulbs in the Animal Kingdom, but they do have some neat behaviors.  A neat behavior in our fish is that they respond to above-water movement.  Notice what they do if you move close to the edge of the pond.  Then sit perfectly still and quiet for two minutes and notice the fish moving back into the open.  Then wave your arms and observe again.  Why do you think the fish exhibit this behavior?  Isn't it fun to interact with a fish?  Hiding in response to moving above-water things is not a behavior fish learn, which makes sense, if you think about what would have to happen for the fish to learn this first-hand (first-fin?).  Mosquitofish are born with this behavior programmed into their DNA - it is an innate behavior.  DNA is the chemical in all organisms' cells that instructs the cells how to build the organism.  Your DNA contains instructions for things like your hair color, face shape, and possibly some behaviors, though scientists are not yet sure about how many human behaviors are innate. 

Mosquitofish with some tail fin damage, likely from hungry mosquitofish 'friends'.

If you catch a mosquitofish or two with a net and put them in a glass bowl, you can observe their fins.  All mosquitofish have a dorsal fin on their back, a tail fin, two pectoral fins (see the top picture), anal fins on their lower surface, and pelvic fins in front of the anal fins.  See labeled fish fins here.  Male mosquitofish have pointy pelvic fins, which you can see in the picture below.  Females have larger, rounded pelvic fins.  Usually females are bigger than the males.  They are more likely to eat any type of food, they grow faster, and they spend lots of their bodies' energy on producing offspring.  Next time you are at the pond, find both male and female mosquitofish by comparing the body size of the fish.

Male mosquitofish revealing its pointy pelvic fin.  Females are larger and have a rounded pelvic fin.

Mosquitofish are live-bearers, meaning they give birth to live fish instead of laying eggs.  Female mosquitofish can give birth to up to 9 broods of offspring each summer, with up to 100 baby fish in each brood!  No wonder we have so many mosquitofish in our pond! 

Can you find the two mosquitofish swimming above the algae?

Mosquitofish are incredibly tolerant organisms, and they will live just fine in almost any reasonable conditions.  This means mosquitofish are great organisms to bring back to the classroom for a day or more to observe closely.  You can keep them in a glass or plastic container with 3-4 inches of water and feed them a tiny bit of fish food.  If you only want to keep them for a day or two, you can even feed them a variety of tiny bits of people food.  If you keep them a longer time, change out about half the tank water every couple of days.  With fish in the classroom, you can look for male and female fish, observe other behaviors or figure out what they like to eat.  You could also investigate the hiding response to moving things.  You could see if they are equally scared of light or dark objects.  You could see how long it takes for them to come out from under a leaf after being scared.  You could see if they hide less after seeing the same object ten times - maybe they learn that some moving things are not harmful!  If that is the case, you would be able to say you taught a fish!

Now that we've seen several organisms in our outdoor classroom, it might be interesting to start a food web of our ecosystem on a large piece of butcher paper.  A food web shows organisms with arrows showing who eats what.  The arrows go from food to consumer, representing transfer of energy and matter from the food into the eater.  So far, we can put algae, snails, dragonflies, bees, mosquitoes, mosquitofish, squirrels and walnut trees on a food web, and we will be able to add many more as the year progresses.  Here's what a small food web looks like. 

In Praise of Black Walnuts

You might want to wear a hard hat next time you go to the outdoor classroom.  There is a black walnut tree in the back corner, and it's walnut season!  If you sit there long enough, you might just witness the loud thud of a walnut hitting the ground.

Here's our black walnut tree.

Black walnuts (Juglans nigra, meaning black Jupiter nut) are beautiful trees.  I like them because they provide light shade (not too dark - their leaves are sparse and let the light through), give us delicious nuts, provide food for squirrels and are an excellent source of wood.  The dark walnut wood is so beautiful, strong and light that a full-grown walnut tree can be worth $5000 or more if it is cut down and sold for wood.  Plant a few walnut trees today and harvest them in 30 years for an excellent return on your investment.  Plus you can eat the walnuts in the mean time!  Just be sure to re-plant what you harvest.

Whole in-shell walnuts are available  in grocery stores this time of year.  They are a great snack, and since they take a while to crack open, you can't spoil your dinner with them.  The grocery store walnuts are English walnuts and ours a black walnuts, but our walnuts are still very good to eat.  In fact, their strong wal-nutty flavor makes them superior for adding to ice cream, fudge and cakes.  You just have to catch them before the animals do.

A black walnut with the husk still on.

Walnuts grow with a husk on them that makes them look like big round limes.  The husk contains a chemical called juglone that makes it smell rather pungent and stain your hands brown if you touch it too much (it won't hurt you, but you can't wash it off).  The juglone in the walnut husks also seeps into the ground under walnut trees and prevents some plants from growing, which helps prevent walnut trees from having too many competitors for sunlight and soil nutrients.  This plant warfare technique is called allelopathy, and it's fairly common among plants to have secret chemical wars going on in the soil.  Smell a walnut husk and notice the bitter juglone smell.  You can also smell the same odor in crushed walnut leaves.  Every fall, the walnut leaves fall and add a new dose of juglone to the soil.  Juglone is also a potent dye and is used by dye-makers to color fabric.  You could try this out by soaking a cloth in crushed walnut husks and water.

Black walnut with squirrel teeth marks in the husk - I bet that tasted awful!

My dad taught me a special technique for removing walnut husks: put a bunch of walnuts in your driveway and drive back and forth on them.  You should be left with a bunch of crumbled husks and intact walnuts.  You could also just wait for the husk to turn black and rot away, but by that time your walnut has probably become infested with worms or fungi.

Chewed hole in a walnut shell with the entire nut removed by a squirrel.

After you remove a walnut husk, the next challenge is to open the walnut shell.  Black walnuts have stronger shells than English walnuts.  My dad's trick for walnut shells is to wrap several walnuts in an old towel and bash them with a hammer.  Very fun.  Then you can use tweezers and a nut pick to pick out the walnut pieces from the shells.  It's a messy business, but totally worth it.

Whole walnut with husk, walnut with husk partially chewed, walnut without husk, and opened walnut.

Search around the bottom of our walnut tree and look for walnuts with the husk on, with a rotted husk, with the husk gone and with the shell open.  Look closely and you will find walnuts with teeth marks from the industrious squirrels that like walnuts for the same reasons we do.  Squirrels have gigantic, orange chisel-like teeth that you can see here.  They scrape their teeth through the husk (ick!) and the shell, then dig out the walnut with their teeth, tongue and claws.  If there are enough new green walnuts, you might want to take one with you and open it yourself - they are delicious!

Black walnut tree.  If you click on the picture, you can zoom in a see clusters of walnuts.

Walnut trees do not grow walnuts in order to provide us with snacks.  The walnuts are actually the offspring of the walnut trees.  The nut part is actually a seed.  If you put a whole in-shell walnut in the ground this fall, it will sprout and grow a new walnut tree in the spring.  The food value of the walnut - the part we like to eat - provides food for the new walnut tree until it can grow enough leaves to use the sun for food.

Here's more information on harvesting black walnuts if you'd like to do a more serious walnut harvest.

Slimy Snails

Ever walked down a beach at the ocean and picked up sea shells?  These are the exoskeletons of a group of organisms known as Mollusks.  Mollusks are defined as soft-bodied invertebrate (no backbone) animals with a hard protective shell usually made of calcium carbonate (and slugs, which have no shell).  Most Mollusks live in oceans, but a few live in non-salty habitats, including ponds and damp environments like the forest floor.

Freshwater snails in our pond.

Snails are Mollusks with spiral shells, eyes on stalks that look like antennae, and a muscular foot for gliding along surfaces.  Here's a neat diagram of snail anatomy to get a sense of snails' body parts.  The pond at our outdoor classroom is teeming with snails!  If you sit and look into the pond for a minute, you'll start to notice black globs moving very, very slowly.  Pick one up - they don't bite - they really only eat plant material.  You now have a snail in your hand.  Say hello to your snail.  S/he will probably not be very happy to see you, which s/he will demonstrate by curling up into his/her shell.  S/he thinks you're going to eat him/her.

Snail recoiling into his/her shell for protection.

OK - this post is starting to get annoying!  What's with all the gender slashes?  Well, it turns out that most snails are both male and female, which is actually pretty neat. 

Snails breathe oxygen, just like we do.  Some use lungs and others use gills for breathing.  You'd think that land snails would use lungs and pond snails would use gills, but it's not that simple.  You'll find some of each kind both above and below the surface of the water.  You'll have to decide what you think about our snails' breathing method.  If they touch the surface every once in a while, they have lungs.  If they never come up, they are either dead or breathe using gills.  Since there are over 4000 species (types) of freshwater snails, and they are very difficult to tell apart, I cannot tell you what kinds we have.

Snail scaling the rocks behind our waterfall on a DIY trail of slime.

I know what you'd really like to ask is, "what's the deal with snail slime?"  Well, snails are gliders.  If you've ever tried to slide down a Slip 'N Slide without water, you know that you get stuck and it's no fun.  Well, snail slime works like water for a Slip 'N Slide, but much, much slower.  The snail constantly makes slime, slathers it across the surface of whatever it's gliding on, and makes itself a slippery trail.  Snails wave their muscles in their foot (the part of their body that contacts the ground) and push themselves along.  Whee!  If you place a snail on a piece of glass or clear plastic and watch from underneath, you can observe this phenomenon.  You may also see the snail's mouth as it drags along the glass trying to scrape up any bits of plant matter.  An interesting fact about snail slime is that you can buy a face cream made with it here.  I don't know why you would want to do such a thing, but if you really want to, it would be much cheaper just to let snails glide on your face.  In case you're not grossed out enough already, humans make a very similar substance in our bodies - mucus.  Mucus helps keep the insides of our mouths, lungs, stomachs and noses slippery so they don't get stuck together.

Blob of snail eggs on algae.

Snail populations work on a boom and bust cycle.  Where there is a lot of plant material available, such as decomposing leaves or algae, snails have enough food to produce a lot of offspring.  Our pond has lots of plant food available, so there are a lot of snails.  If you look carefully at a clump of algae from the pond, you may see a lump of clear gel balls - those are snail eggs.  When all the plant material is gone, the snails will mostly die off, but they will repopulate again when nutrients are available.  It's easy to keep snails in an aquarium, as long as you offer them some lettuce or algae from time to time.  Be careful though, if you leave too much lettuce in the tank, you will end up with hundreds of snails!

The most common type of snail in our pond.

Since our snails require fresh water to survive, and snails were not intentionally added to our pond, where do you think they came from?  There are two likely answers.  One is that snails or snail eggs were attached to the aquatic plants that were planted in our pond.  The other explanation is that snail eggs are sticky (from snail slime!), and they sometimes stick to birds' legs.  Any water birds that have visited our pond could bring or take snail eggs to or from our pond.

Another type of snail found in our pond, plus some neat clouds reflected in the water.