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.