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I saw this critter in Hawaiian Paradise Park on the east side of the Big Island (Hawai’i) south of Hilo. I first saw a larger one that was gray-bodied and it had the same fan-shaped head. At first I thought it was a kind of earthworm or other kind of worm. But when I photographed this 2.5 in. one with the yellowish body and dark dorsal line, I noticed what appeared to be a slime trail. The larger gray one was about 6-7 in. long with a uniform thin body (not segmented like an earthworm), perhaps a bit thinner in aspect ratio that his one. It seemed to move faster than the typical slugs in Hawaii (Veronicella cubensis?) but perhaps it was the more animated movement of the fan-shaped head that created that illusion. The points of the head articulated like a slug’s "antennae". I didn’t want to turn it over to examine the ventral side. Might this be a juvenile form? Any idea what it is?
Les Chibana
Volcano, HI

Hi Les,
Thanks for sending this unusually colored Arrowhead Flatworm, a Planarium.

Update (04/26/2006): Arrowhead Flatworm in Maui
Aloha, I am impressed with the photo you just put up on your home page from the Big Island. We found this Arrowhead Flatworm in our outdoor shower a month ago, just after several days of rain. It was 4″ long and yellowish with black stripes down the entire length of it’s body. We had never seen one before so I contacted our local Dept. of Ag to inquire if it is considered an invasive species. Apparently the answer depends on your point of view. If you want earthworms for your garden, then the flatworm is invasive. If you have an abundance of the Giant African Snail, then you may appreciate the flatworm as it is a predator of said snail. I read on the internet that the flatworm expands to over twice it’s size after eating, but I have yet to find an earthworm to feed to it. It would not touch my composting worms. Keep up the excellent and entertaining work on your website! It is much appreciated. Aloha,
Michelle
Kihei, HI

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1. Mating Hawaiian Snails (February 21, 2006)
2. Arrowhead Flatworm (May 15, 2008)
3. Arrowhead Flatworm (March 13, 2007)
4. Arrowhead Flatworm (April 2, 2006)
5. Arrowhead Flatworm (August 8, 2009)