The Headworm is a parasitic invertebrate that lives in the trees of a few Oceanykan jungles. It does not inhabitate most of the country, but there are some small areas where their concentrations are high. These areas change as headworms are migratory due to their reproduction cycle.
They burrow themselves into the necks of humans which they reach by falling on them from a tree. The host human is, in a few minutes, under the influence of the headworm, which begins planting eggs inside the host's neck. For weeks the host looks for anything to feast on, specially other humans, which rapidly raise muscle and fat while filling the stomach and intestines. No defecation and minimal nutrient absorption occur. After about a month, the host dies of a burst stomach or starvation. The headworm eggs hatch and develop inside the now massive and morbidly obese human.
In ancient times, headworm infestations were countered by burning the affected patches of land, as well as its victims. This tradition is still alive in the use of flamethrowers to exterminate them. Jungle dwellers are advised to strap a rigid cloth on their necks, and use large headwear.