(ORDO NEWS) — The hammerhead worm (Bipalium sp.) is a terrifying, poisonous terrestrial flatworm. This large worm lives on land and is both a predator and a cannibal.
Although these creepy-looking worms do not pose a direct threat to humans, they are an invasive species that can destroy earthworms.
Fast Facts: Hammer Worm
- Scientific name: Bipalium sp.
- Other names: Broad-headed planarian, “terrestrial”.
- Distinguishing Features: A large ground planarian with a spade-shaped head and a ventral foot or “creeping sole”.
- Size range: From 5 cm (B. adventitium) to over 20 cm in length (B. kewense).
- Diet: Carnivorous, feeding on earthworms and each other.
- Lifespan: Potentially immortal
- Habitat: Widespread throughout the world, preferring moist, warm habitats.
- Conservation status: Not assessed
- Kingdom: Animalia
- Phylum: Platyhelminthes
- Class: Rhabditophora
- Order: Tricladida
- Family: Geoplanidae
Fun fact: The hammerhead worm is one of the few terrestrial invertebrates that produces the neurotoxin tetrodotoxin.
The most characteristic features of the hammerhead are its fan-shaped or spade-shaped head and long, flattened body. On the underside of the planaria there is a large “creeping sole” used for locomotion. Species are distinguished by head shape, size, coloration, and stripe pattern.
Terrestrial planarians are terrestrial in color, found in shades of grey, brown, golden, and green. Small hammerhead worms include B. adventitium, which varies from 5 to 8 cm (2.0 to 3.1 in) in length. In contrast, adult B. kewense worms can exceed 20 cm in length.
The hammerhead worm has a long, flattened body and a broad head.
Hammerheads are native to tropical and subtropical regions but have become invasive throughout the world. It is believed that these planarians were accidentally introduced and distributed on rooted garden plants. Since hammerheads require moisture, they are rarely found in desert and mountain biomes.
Bipalium worms are carnivorous, preying on earthworms, slugs, insect larvae and each other. Worms detect prey using chemoreceptors located under the head or in the ventral groove. The hammerhead worm hunts down its prey, presses it to the surface and entangles it with mucous secretions.
When the prey is mostly immobilized, the worm protrudes its pharynx out of its body and secretes digestive enzymes, then sucks the liquefied tissue into its branched intestine using cilia. When digestion is complete, the worm’s mouth also serves as its anus.
Hammerheads store food in vacuoles in their digestive epithelium. The worm can live for several weeks on its stores and will cannibalize its own tissues for food.
Bipalium kewense captures the earthworm. Researchers believe that the planarian secretes a toxin to immobilize its prey.
Although some types of worms are edible, the hammerhead worm is not one of them. Planaria contains a powerful neurotoxin, tetrodotoxin, which the worm uses to immobilize prey and scare away predators. The toxin has also been found in pufferfish, blue-ringed octopuses, and rough newts, but no species of terrestrial invertebrate was known prior to its discovery in the hammerhead.
Hammerhead worms are erroneously called hammerhead slugs because they move like slugs. They use the cilia on their crawling soles to glide across the slime strip. Worms have also been observed descending down the thread of mucus.
Terrestrial planarians are photo-negative (light-sensitive) and need high humidity. Therefore, they usually move and feed at night. They prefer cool, damp places, usually dwelling under rocks, logs, or shrubs.
Reproduction and regeneration
Worms are hermaphrodites, each individual has both testes and ovaries. The hammerhead worm can exchange gametes with another worm through its secretions. Fertilized eggs develop inside the body and are expelled to the outside in the form of egg capsules. After about three weeks, the eggs hatch and the worms become sexually mature. In some species, juveniles differ in coloration from adults.
However, asexual reproduction is much more common than sexual reproduction. Hammerhead worms, like other planarians, are essentially immortal.
Typically, the worm reproduces by fragmentation, leaving behind the tip of its tail adhering to a leaf or other substrate, which then develops into an adult. If the worm is cut into pieces, each piece can regenerate into a fully developed organism within a few weeks. Wounded worms quickly repair damaged tissues.
No hammerhead species has been assessed for inclusion in the IUCN Red List, but there is no evidence that their numbers are threatened. Terrestrial planarians are widely distributed in their natural tropical and subtropical habitats and have spread their territory throughout the world. Having settled in the greenhouse, the animals settle in the surroundings. In colder climates, worms are able to tolerate low temperatures by seeking sheltered places.
At one time, researchers feared that terrestrial planarians could damage plants. Over time, they were recognized as harmless to greenery, but then a more insidious threat appeared. Hammer worms are capable of decimating earthworm populations.
Earthworms are vital as they aerate and fertilize the soil. Hammerhead worms are considered a dangerous invasive species. Some methods used to control slugs also work on flatworms, but their long-term impact on ecosystems has not yet been fully determined.
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