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.