Hammerhead Worm

I found this hammerhead worm, Bipalium species in my car shed being teased by ants. I was using Canon EF 100mm f/2.8L Macro IS on Canon EOS 5D Mark III with Canon Speedlite 580EX II Flash which was not very adequately diffused. The bare flash, despite my feeble attempts to diuffuse it, caused some amount of specular highlights on this shiny flat worm. Ants were defensive against the worm but hesitant to bite it. Bipalium is a genus of large predatory land flatworms, Land planarians.

Land planarians are soft, bilaterally symmetric, dorsally-ventrally flattened worms, 3 to 50 cm long by 0.2 to 0.5 cm wide. They lack a respiratory and circulatory system, a skeleton, and an anus. Heads of many land planarians are expanded lunate or tapering to a blunt point. Eyespots may be present on the head. They are often loosely called “hammerhead worms” or “broadhead planarians” because of the distinctive shape of their head region.

Reproduction in Bipalium may be asexual or sexual and all species are hermaphroditic. Asexual reproduction is principally by fragmentation at the posterior end. Lateral margins pinch in about 1 cm from the tail tip. Severance occurs when the posterior fragment adheres to the substrate and the parent worm pulls away. The posterior fragment is motile immediately, and within seven to 10 days a lightly pigmented head begins to form. One to two fragments are released each month.

Fragmentation is the primary form of reproduction, but the flatworm will also lay eggs in a cocoon. At first the cocoon is bright red, but within 24 hours it turns black. Eggs will hatch about 21 days later depending on temperature and moisture conditions.

There is very little known about the ecology of these worms. Because of their cannibalistic habit, land planarians may be their own worst enemy. Because land planarians are photo-negative during daylight hours and require high humidity, they are found in dark, cool, moist areas under objects such as rocks, logs, in debris, or under shrubs, and on the soil surface following heavy rains. Movement and feeding occur at night. High humidity is essential to survival. They can survive desiccation only if water loss does not exceed 45 percent of their body weight. Land planarians are most abundant in monsoon period in India.

They also seem to have a neurotoxin called Tetrodotoxin evenly distributed throughout the body deterring their common predators like lizards & salamanders. May be that also is why ants were not willing to attack it.

Land planarians glide smoothly on the substrate by the action of powerful, closely spaced cilia in a special medial ventral strip (creeping sole), on a thin coat of mucus secreted on the substrate by glands opening into the creeping sole. Land planarians that migrate on plants or objects above the ground sometimes regain the ground by lowering themselves down by a string of mucus.

Land planarians devour earthworms, slugs, insect larvae, and are cannibalistic. Prey are located by chemoreceptors located in a single ciliated pit under the head or in a ciliated ventral groove. Struggling prey are held to the substrate and entangled in slimy secretions from the planarian. The pharynx is protruded from the mouth and into the prey. Food is reduced to small particles prior to entering the gastrovascular cavity. The food particles are taken by epithelial cells in amoeboid fashion and formed into food vacuoles. Planaria store food in digestive epithelium and can survive many weeks shrinking slowly in size without feeding. They are capable of utilizing their own tissues such as reproductive tissue for food when reserves are exhausted.