The Hammerhead Worm in Thailand

This morning I found an elegant creature on the tiles outside the bathroom at Dokmai Garden (Chiang Mai, Thailand). It was the ‘Hammerhead Worm’, Bipalium kewense. It slithered, leaving a trail of mucus behind it, like a slug. However, this is not a slug (phylum Mollusca) or a common segmented worm (phylum Annelida), but a flatworm or planarian, belonging to an entirely different phylum of organisms (Platyhelminthes). The mouth also serves as anus, and it is situated in the middle of the underside. It reproduces by eggs and fragmentation.

According to a University of Florida publication, this species is native to Southeast Asia, but has spread to all forested continents via greenhouse pots. The name ‘kewense’ alludes to its discovery at Kew Gardens, Richmond/London, in 1878.

It feeds on slugs, snails, insect larvae, earthworms and other land planarians. In that respect it seems like a useful predator in your monsoon garden. However, concerns have been raised in areas where it is invasive, that it may eradicate earthworms, which serve as important aerators and soil makers. As the hammerhead worm is native to Thailand, and since Dokmai Garden is far richer in earthworms than in hammerhead worms, I guess this is just another rare cheetah hunting the prolific zebras. Nobody would start killing birds or carabid beetles because they eat earthworms. The hammerhead worm’s worst enemies would be microbes and other land planarians. Although it thrives in moist conditions, it can endure droughts and freezing temperatures until the conditions are favourable again. 

As there are many legends about this creature, use the scientific name when googling, so that you acquire more trustworthy information.

This is a beautiful creature! The hammerhead is packed with eyespots and one nostril.