Amazing Spiders

The Golden silk Orb-weaver (Trichonephila clavipes) is a large
orb-weaver found in the Southeastern United States, Mexico, Central and
South America.  Another common name is Banana Spider. 
Palm Beach County, Florida.

Spiders hold a special place in the human psyche.  They are both feared and revered.  Many people suffer from arachnophobia, the fear of spiders.  This fear comes in part because all spiders produce venom that they use to paralyze or kill their prey.  A bite by members of a handful of species is painful but rarely fatal to people.  Two of the dangerous spiders found in the Southeastern United States are the Brown Recluse and the Black Widow.  But spiders are not hunting us. When spiders bite people it usually comes from accidently disturbing the spider.  Beyond the fear, spiders are honored in many cultures.  The nursery rhyme about an Eensy-weensy spider teaches young children persistence.  Anansi, the trickster spider of West African folklore, outwits the powerful and became a symbol of resistance for slaves in the Americas.  The twentieth century American mythos gave us The Amazing Spider-Man. In this familiar tale a radioactive spider bites mild-mannered Peter Parker and he takes on spider characteristics including wall climbing and web slinging . 

 

A spider exoskeleton left in a web after molting.
Mecklenburg County, North Carolina.

Spiders are a major group in the class Arachnida that also contains ticks, mites, scorpions and horseshoe crabs.  Spiders have eight jointed legs, a cephalothorax and abdomen, fangs that inject venom and silk-producing organs in the abdomen.  Spiders have an exoskeleton and go through several molts to achieve the adult size.  A molting spider’s exoskeleton will split along the top of the cephalothorax and the spider will crawl out leaving the old exoskeleton behind.  Female spiders are often larger than the males and in some species the female eats the male after mating.  With nearly 50,000 described species, spiders are a very successful group and live on all continents except Antarctica. 

 

Web of an orb-weaver spider.  This web shows the radial and spiral silk
threads typical of this group. The spider is waiting in the middle.
Rowan County, North Carolina.

Detail of an orb-weaver spider web decorated with dew. 
Rowan County, North Carolina.

The silken web of spiders is one of their most interesting features.  Silk is a protein that is strong and light.   Spiders use their webs to catch prey on silk threads. Spiders have other uses for their silk.  They can suspend themselves by a thread; some use it to weave egg cases and others use threads to fly.  That’s right, some spiders can fly.  A spiderling can shoot fine silk threads from structures called spinnerets.  The threads catches a breeze and off fly the baby spiders. This amazing feat is called ballooning and allows spiders to disperse over long distances.  Ballooning spiders are among the first predators to arrive on newly formed volcanic islands.   

 

Yellow Garden Spider (Argiope aurantia) is also know as the Writing Spider.
Rowan County, North Carolina.

Closeup view of the Yellow Garden Spider on its web.
The body of females may be over an inch long. 
Rowan County, North Carolina.

Spiny Orb-weaver (Gasteracantha cancriformis).  This orb-weaver has a large
abdomen with red spines.  The specific name is from Latin meaning "crab form" and its
resemblance to a crab is evident.  Mecklenburg County, North Carolina.

One common group of spiders is the Orb-weavers in the family Araneidae.  These spiders are often brightly colored and make the familiar web with radial strands and circular threads.  Their webs can be quite large and are usually vertically oriented.  Most people have the experience of walking through the woods and getting a face-full of Orb-weaver web.  Some Orb-weavers,  called Writing Spiders, weave a zigzag design in the center of web.  This may help attract prey to the web or allow the spider to hide in the center.  Orb-weavers usually make a new web each day.  The spider eats the old web, digests the silk protein and reuses it in the next-day’s web. 

 

Marbled Orb-weaver (Araneus marmoreus).  This spider has a leaf fragment
caught in her web and is removing it.  Rowan County, North Carolina.

This female Marbled Orb-weaver's abdomen is very large and she is 
about to lay eggs. Another common name of this spider is Pumpkin Spider,
for obvious reasons.  Marbled Orb-weavers are found in Europe, Asia 
and North America.  Rowan County North Carolina.  

Orchard Orb-weaver (Leucauge venusta).  This spider makes a horizontal web
and has delicate green and yellow markings on the abdomen. 
Rowan County, North Carolina.

Arrowhead Orb-weaver (Verrucosa arenata) has a large,
white triangular shield on its abdomen. 
Mecklenburg County, North Carolina. 

The body of Golden Silk Orb-weavers can be over 2.5 inches long. 
Its web is very strong and yellow in color. 
Palm Beach County, Florida. 

Some spiders do not use a web to capture their prey.  A major group is the Wolf Spiders in the family Lycosidae.  These spiders have eight eyes and make burrows in the soil.  Wolf spiders rush from their burrows and chase down their prey.  Female Wolf Spiders make a silk egg case and carry their eggs with them.  After the eggs hatch, the tiny spiders ride on the female’s abdomen. 

 

Wolf Spiders (Tigrosa sp) do not make webs but like wolves,
run across the ground hunting their prey.
This female is carrying her silk egg case behind her.
Rowan County, North Carolina. 

Another group of spiders that do not make webs is the Ground Crab Spiders in the genus Xysticus.  Ground Crab Spiders are ambush predators.  They wait for a small animal to come by, seize it with their long front legs and kill it with a venomous bite. 

 

Ground Crab Spider (Xysticus sp).  This spider waits to ambush
its prey rather than making a web. Rowan County, North Carolina.

Fall is coming on and spiders are abundant now.  With the first frost, some adult spiders will hibernate and others will die.  Many baby spiders will spend the winter tucked into a silk egg case.  When spring comes, the juvenile spider will emerge and begin another year of amazing activity.  

Tiny orb-weaver spiderlings are setting out into the world.
Mecklenburg County, North Carolina.

Weird Worms

 

Broad-headed Planarian (Bipalium kewense). 
This large flatworm has a shovel shaped head and preys on earthworms. 

I saw weird worms two days in a row.  While walking around my neighborhood, I saw a worm crawling on the sidewalk and thought, “That is a really long earthworm”.  When I took a second look, I saw its head was much wider than the body so I knew this was something different.  I took a quick phone photo and walked on.  The next day I saw another of these bigheaded worms so I picked it up and carried it home in a tissue. 

Some internet searching disclosed it was not a segmented worm, like an earthworm, but a giant flatworm.  Flatworms are in the Phylum Platyhelminthes, a group which includes the parasitic tapeworms, flukes and flatworms (the planarians).  Flatworms have a single opening to the digestive system so its food comes in and the waste exits from the mouth. Flatworms move by a combination of muscular contraction and a structure called a creeping sole that secretes a slime layer and has cilia to aid in locomotion.  The planarian claim to fame in developmental biology is, if you cut the worm in half, each half can regenerate an entire worm.

Bipalium kewense crawling on a 
wet sidewalk.

Both the worms I found were Bipalium kewense, a giant predatory flatworm. Bipalium kewense has several very descriptive common names including; Hammerhead Worm, Broad-headed Planarian, Shovel-headed Garden Worm and Arrowhead Worm. Bipalium kewense was discovered in 1878 in a greenhouse of the Royal Botanic Gardens at Kew, England.  The worm probably originated in Southeast Asia and has been introduced around the world in the plant trade. Bipalium kewense is considered an invasive species in the United States. 

 

Video of Bipalium kewense crawling.  The final scene of this video is courtesy of 

Dr. Carmony Hartwig and shows Bipalium consuming an earthworm.  

The natural habitat for Bipalium kewense is leaf litter and soil where it is a voracious predator of earthworms and other invertebrates.  This invasive worm can do economic damage to earthworm farms, decimating the beds.  I photographed and videoed the worm I collected against different backgrounds. In the worst tradition of wildlife filmmakers, who in times past would put predator and prey together to see what would happen, I put an earthworm in the path of Bipalium kewense.  The flatworm and earthworm crawled around each other but no violence ensued.  But, my friend Dr. Carmony Hartwig found one of these planarians eating an earthworm and made a graphic video.  After completing photography, I returned the worm to where I found it.  I wondered if that was the right thing to do since it is an invasive species. 

Bipalium is a very large worm.  This specimen was about seven inches long.

I have never seen Broad-headed Planarians before and now two blundered into my path in the same week.  The weather has been rainy and many worms are crawling on sidewalks and roads.  But, I can’t help but wonder if something else is going on.  Do my observations mean this invasive species is experiencing a population increase?  Does it reflect an increase in the earthworm population? Is it the result of climate change?  I will be watching for more of these weird worms.

 

Nettles

Spurge Nettle (Cnidosculus stimulosus) grows in dry,
sandy soil.  This plant was one of a group in Weymouth Woods State Park,
Moore County, North Carolina.

When I hear the word nettle, my skin starts to itch.  The name accurately describes what these plants do.  Brush up against a nettle and you get pain, itching and inflammation.  Hairs on the stems and leaves of nettles may contain powerful toxins that cause a painful reaction called urticaria.  The plant structures that cause this uncomfortable condition are urticating hairs.  There are several plants in the Southeastern United States called nettles, but they are not closely related to each other.  All these nettles share a common feature, hairs or spines on the stems and leaves.  These structures often contain noxious chemicals and deter grazing animals.  

Solanum carolinense or Horse Nettle is a relative of potato and tomato. 
Horse Nettle is a common plant in fields and along roadsides. 
Rowan County, North Carolina.

A closeup view of Horse Nettle flowers with their five white
petals and five bright yellow anthers.
Rowan County, North Carolina.

Horse Nettle (Solanum carolinense) is a member of the Nightshade family, the Solanaceae.  This family  family includes many familiar plants; potato (Solanum tubersum) and tomato (Solanum lycopersicum), tobacco (Nicotiana tabacum) and Deadly Nightshade (Atropa belladonna).  Horse Nettle is a low-growing herb with lobed leaves.  The leaves and stems bear hairs and large hooked spines.  Horse Nettle produces blueish-white flowers that have five petals and five bright yellow anthers.  The fruits look like yellow cherry tomatoes and each contains dozens of seeds.  Horse Nettle is one of the most toxic plants in this part of the world because they produce solanine glycoalkaloids.  When ingested solanine glycoalkaloids cause nausea, vomiting, headache and even death.  These toxins are in the leaves, stems and fruits, so no part of the plant is safe to consume.

 

Horse Nettle leaves and stems have large spines. 
Rowan County, North Carolina.  

A maturing fruit of Horse Nettle looking very
much like its close relative, tomato.
Rowan County, North Carolina

The Horse Nettle fruit on the left is nearly ripe. The
others will turn yellow in a few days.
Rowan County, North Carolina.

Wood Nettle (Laportea canadensis) is a true nettle in the family Urticaceae.  Wood Nettle grows in Eastern North America near water as a member of the forest understory.  This plant has large bright green leaves that bear stinging hairs.  The hairs break off in the skin and release neurotoxins that cause sharp pain and raise a rash that can last for several days.  Despite their threat of pain, many people harvest and eat Wood Nettles.  These hardy folks boil the plants and this inactivates the toxins.  Wood Nettle is reputed to taste like spinach. 

 

Wood Nettle plant growing on the flood plain
of the Yadkin River.  Rowan County, North Carolina.

The stinging hairs of Wood Nettle.
These fine hairs contain toxins that give a painful sting.
Rowan County, North Carolina. 

The third species on this nettle tour is Spurge Nettle.  It has a marvelous scientific name, Cnidoscolus simulosus and grasping this plant is definitely a stimulating experience.  Spurge Nettle is in the family Euphorbiaceae and is primarily a plant of the Southeastern Coastal Plain where it grows in dry, sandy habitats.  This plant has large, dark green, lobed leaves and produces white flowers with five petals. The fruits of Spurge Nettle are capsules and each contains three seeds.  Of course, since it is a nettle, the leaves, stems and fruits are covered with urticating hairs that contain chemical irritants. Spurge Nettle has a large, starchy taproot that after boiling tastes like pasta.    

 

Spurge Nettle in flower.
Moore County, North Carolina.

Flowers and developing fruits of Spurge Nettle.
Moore County, North Carolina.

Closeup of the utricating hairs of Spurge Nettle.  
Moore County, North Carolina. 

The three-chambered fruit of Spurge Nettle.  Like the rest of the plant,
the fruits are covered with stinging hairs.
Moore County, North Carolina.

People all over the world have a complex relationship with nettles.  North American nettles may be poisonous, sting when touched and some are edible.  Folk medicine traditions describe many uses of nettle from treating asthma and kidney ailments to preventing baldness.  The Tibetan holy man, Milarepa, is said to have lived to a ripe old age in his mountain fastness by eating only nettles.  A side effect of this diet was his skin and hair turned green.  I make no recommendations on nettles as food or medicine, but they are attention grabbing members of our flora.   

The Sphinx, the Weed and the Parasite

 

Carolina Sphinx Moth (Manduca sexta) hovering
over the flower of Sacred Datura (Datura wrightii). 
The moth's proboscis is extended toward the flower.
Rowan County, North Carolina.

This is a story of the integration of three lives.  The sphinx is a giant moth whose caterpillar is a major agricultural pest.  The weed is Jimsonweed is a handsome plant with large showy flowers and produces hallucinogenic compounds.  The parasite is a wasp that lays its eggs in the larva of the Sphinx and new wasps burst forth like aliens from the chest of an unfortunate sci-fi character. 

 

Sacred Datura plant flowering at night.
Rowan County, North Carolina.

First the weed, Jimsonweed.  It goes by many names.  Its scientific name is Datura wrightii, also known as Sacred Datura and it is native to the Southewestern United States and Mexico.  We have several plants in our yard that came to us by way of Austin, Texas.  There are several Jimsonweed species and they are in the same family as potato, the Solanaceae.  This interesting and important plant family includes other well-known plants like Tomato, Tobacco, Eggplant, Pepper and Deadly Nightshade.

Sacred Datura is a desert plant with large gray-green leaves and, as expected from a desert plant, is quite drought tolerant.  It produces a variety of toxic alkaloids that when consumed can induce profuse sweating, drowsiness, visual impairment, hallucinations, psychosis and even death.   The sacred in the name comes from its use in religious ceremonies of native people in the desert Southwest and Northern Mexico.  One of the active compounds in Sacred Datura is scopolamine, a drug now used to combat motion sickness, usually in the form of a transdermal patch.  In the bad old days of spies and enhanced interrogation, scopolamine was a major ingredient in “truth serum” although its effectiveness is questionable.   

 

Early and nearly mature flower buds of Sacred Datura.
Rowan County, North Carolina.

Sacred Datura flower on the afternoon the
flower will open.
Rowan County, North Carolina.

Sacred Datura petals on a flower that is about to open.
Rowan County. North Carolina.

Jimsonweed produces abundant, large, white, trumpet-shaped flowers throughout the summer.  The flower shape and color give this plant another of its many common names, Angel Trumpet.   The flowers develop for several days, with the petals rolled up within the green sepals.  Each day the flower gets longer and finally on flowering day the petals emerge and turn white. In late afternoon, the flowers open to show the five petals fused that make the trumpet.  As evening comes, the flowers release a strong and pleasant fragrance reminiscent of gardenia.  The white color and fragrance gives a clue to what Sacred Datura is doing at night.  The plant is sending an unmistakable signal to its pollinator, the Carolina Sphinx Moth (Manduca sexta).  

 

Carolina Sphinx Moth about to feed.
Rowan County, North Carolina.

Carolina Sphinx Moth sipping nectar from a Sacred Datura flower. 
The moth's long proboscis is visible reaching into the flower.
Rowan County, North Carolina.

Carolina Sphinx Moth approaching a Sacred Datura flower.
Rowan County, North Carolina.

Carolina Sphinx Moth has a four-inch wingspan, is dark gray in color and has five paired, orange spots on the sides of its abdomen.  The moth also has a long proboscis, a feeding structure that can be over eight inches long.  The proboscis is the key to the moth’s relationship with the Jimsonweed.  Datura lures the moth in from a distance with is fragrance, gives a visual target with the white flowers. The payoff for the moth is the sugar-rich nectar.  The nectaries for the flower are at the base of the trumpet-shaped tube, eight inches down.  The Carolina Sphinx Moth hovers over and even flies into the flower to collect the nectar.  But collecting nectar is not straightforward.  In order to drink, the moth must thread its proboscis down one of five nectar tubes on the inside of the petals.  

Infrared video of Carolina Sphinx Moth feeding on Sacred Datura.

Rowan County, North Carolina.

More infrared video of Carolina Sphinx Moth feeding on Sacred Datura. 
Rowan County, North Carolina.

While collecting nectar, the moth brushes against the stamens of the flower picking up pollen.  It then flies to another flower and transfers pollen to the female stigma.  There the pollen makes a tube that grows through the stigma, down the style to the ovary at the bottom of the flower.  There the pollen nucleus fuses with the Datura egg.  The fertilized egg and surrounding tissue develops into the seed that is contained in the fruit.  The fruit of Sacred Datura is covered with spines and these give the plant yet another common name, Thornapple. 

 

Sacred Datura the day after flowering.
Rowan County, North Carolina.

Sacred Datura flower two days after flowering.
The sepals and petals have fallen off but the long
style and stigma are still attached to
the developing fruit. 
Rowan County, North Carolina.

The spiny fruit of Sacred Datura showing why another common
name for the plant is Thornapple.
Rowan County, North Carolina.

Mature fruit of Sacred Datura.  The fruit has broken open
and the seeds are visible.
Rowan County, North Carolina.

The Carolina Sphinx Moth comes from a large caterpillar called the Tobacco Hornworm.  This larval stage eats, as the name suggests, tobacco but also thrives on other plants in the same family, including tomato.  A female moth lays an egg on the host plant where the larva grows and molts several times. The final larval stage of Carolina Sphinx Moth is over three inches long and can quickly defoliate the host plant. 

 

Tobacco Hornworm is the caterpillar of Carolina Sphinx Moth.
This caterpillar is on a Tomato (Solanum lycopersicum) and is eating leaves.
The white structures are cocoons of the wasp Cotesia congregate 
that has parasitized the caterpillar.
Rowan County, North Carolina.

This is where the final part of the story comes in, the parasite.  Actually, it is a parasitoid wasp, Cotesia congregate, that injects its eggs inside the body of the Tobacco Hornworm caterpillar.  The wasp eggs hatch and the emergent larvae consume the caterpillar from within.  Two weeks later wasp larvae dissolve their way through the exoskeleton of the caterpillar and make a white cocoon on the outside. Within the cocoon, the wasps metamorphose into their flying form.  These wasps mate and parasitize more Tobacco Hornworms.  A caterpillar parasitized by Cotesia dies before it can transform into a moth so the wasp is an effective form of biological control for Tobacco Hornworm.  

This intricate relationship, this perfection of interaction, between the plant, the moth and the wasp has been honed for millennia by evolution. Sacred Datura attracts and feeds the Carolina Sphinx Moth.  The moth has the sensory system specialized to find the plant at night and a proboscis long enough to reach the nectar supply deep within the flower.  The moth then pollinates the Datura plant.  The wasp Cotesia parasitizes the Tobacco Hornworm to propagate the species.  All the interactions are pieces of an elaborate living puzzle.

POST SCRIPT - About two weeks after posting this blog I noticed the leaves of one of the Datura's were being eaten.  Sure enough, several larvae of Tobacco Hornworm were consuming the leaves.  

The leaves of this Sacred Datura have been eaten.  
Rowan County, North Carolina.

The Carolina Sphinx moths were not only collecting nectar and pollinating the flowers but were also laying eggs on the leaves.  Although it probably does not, this moth can complete its entire life cycle on one plant.  

The Datura leaves were being eaten by several Tobacco Hornworms,
the larvae of the Carolina Sphinx Moth.  Note this caterpillar has not been parasitized
by the Cotesia wasp and is very healthy, measuring in at 3.5 inches.

The Eyes Have It

 

A single inflorescence of Oxeye Daisy, Leucanthemum vulgare.
Yellow disc flowers are surrounded by white ray flowers. 
Rowan County, North Carolina.

Do you ever feel like you’re being watched?  Eyes may be upon you when you walk the woods or meadows.  Several plants in the Southeast got their names because they appear to have eyes.  

 

Blue-eyed Grass,  Sisyrinchium angustifolium flowers in the spring. 
Orange County, North Carolina.

Blue-eyed Grass (Sisyrinchium angustifolium) is the first of the eye plants to flower in the spring.  Blue-eyed Grass is not really a grass but is in the Iris family.  It is a monocot and has flower parts in threes, which is characteristic of that group.  Blue-eyed Grass has three blue petals and three blue sepals.  These petals and sepals look the same so, since there is not enough terminology in botany, they are called tepals.  Blue-eyed Grass leaves are long and narrow so they look like leaves of grass.  Between the blue flowers and the grass-like leaves, the name Blue-eyed Grass was obvious. 

 Two plants with eyes in their names that often occur together in summer fields are Oxeye Daisy (Leucanthemum vulgare) and Black-eyed Susan (Rudbeckia hirta).  Both these plants are in the Sunflower family, the Asteraceae.  

 

A group of Oxeye Daisies in a meadow.  Rowan County, North Carolina.

Despite looking All-American, Oxeye Daisy is native to Eurasia and came to our shores in the early 1900s.  It is now naturalized in the 49 continental states and most Canadian provinces.  Oxeye daisy  is a very successful plant and is considered an invasive species in some states. What appears to be a single flower is really a group of flowers, an inflorescence.   Oxeye Daisy inflorescences are made of two flower types.  The yellow eye in the middle is composed of dozens of disk flowers.  The disk flowers have greatly reduced petals but have pollen-producing anthers and the female carpel with its pollen collecting stigma. The outer rim of the inflorescence that looks like petals are really flowers, the ray flowers.  These flowers have carpels and five fused, white petals that stick out to the side. The ray flowers direct pollinators toward the central disk flowers.  

A single daisy disk flower.  It has five small yellow petals and a
two-lobed stigma above the petals.  The anthers are not visible 
in this picture.  Rowan County, North Carolina.  

Daisy ray flower with five white fused petals and
the stigma.  Rowan County, North Carolina.

This Oxeye Daisy has attracted a couple of predators.  On the right is a crab spider (family Thomisidae) 
and on the left is a ladybird beetle (family Coccinellidae).  Rowan County, North Carolina.

The original scientific name for Oxeye Daisy was Chrysanthemum leucanthemum bestowed by none other than Carl Linnaeus, the godfather of biological classification.  Linnaeus’s scientific name for Oxeye Daisy absolutely sings.  The genus and species names have the same number of syllables and they rhyme.  The original scientific name means “golden flower, white flower”.  Plant taxonomists revised the genus Chrysanthemum in the late 20^th century and renamed Oxeye Daisy Leucanthemum vulgare.  Quite a come down to go from “golden flower, white flower” to “common white flower”. 

 

A stand of Black-eyed Susan (Rudbeckia hirta). 
Rowan County, North Carolina

Black-eyed Susan is native to North America and grows over most of the continent.  It has black disk flowers and bright yellow ray flowers.  Black-eyed Susan flowers attract many pollinating insects and birds eat the mature fruits.

 

A single inflorescence of Black-eyed Susan with black disk flowers 
and yellow ray flowers.  Rowan County, North Carolina. 

Perhaps the strangest plant that might watch you is Doll’s Eyes (Actaea pachypoda).  This member of the Buttercup family grows in the eastern United States and Canadian provinces.  In North Carolina, it is most often found in mountain forests.  Doll’s Eyes produce white flowers in the spring and during summer makes white fruits with a single black dot that gives the plant its name.  Another common name for this plant is White Baneberry.  That name is a warning since the fruits and other plant parts are poisonous.  When eaten by people, Doll's Eyes fruits depress cardiac function and may cause death.  The toxins do not affect birds that eat the fruits and disperse the seeds of this interesting plant. 

 

A Doll's Eye plant with white fruits. Watauga County, North Carolina.

A closeup view of Doll's Eye fruits.  The fruits are white and spherical
and each bears a black spot that gives them their doll eye appearance.
Watauga County, North Carolina.

Be careful while hiking, these plants may be watching you.  The beauty of these plants may be in the eye of the beholder.