Devil Weed and Invasive Snails

The Hawaiian Islands were once home to approximately 750 species of native snails. The Hawaiian saying, “ke kāhuli leo le‘a o ka nahele,” is a compliment meaning a person has a voice as sweet as the song of a forest snail. The often colorful jewel like snails were so abundant in the trees and on the ground, that the song of the kāhuli snail was said to be the wind whistling through their shells.

Today, an estimated 90% of endemic Hawaiian snail species are extinct. Over-collection, loss of habitat, climate change, and introduced predators have all contributed to their disappearance.

The giant African land snail (Achatina fulica) was introduced to the Hawaiian Islands in 1936 as an exotic pet. It can grow up to 8 inches (20 cm) and weigh up to two pounds (1kg). In their native Africa, the giant snails are a popular food. In some places, they are hard to find in the wild due to over harvesting.

The giant African land snail has a voracious appetite that makes it the most ecologically damaging invasive land snail. Besides devouring vegetation and crops, it can transmit deadly parasites like rat-lungworm disease (Angiostrongylus cantonensis). The parasites are transmitted to the snails when they eat infected rat feces. People can become infected with the parasitic roundworm by eating raw snails—usually by eating baby snails by mistake in unwashed salads. The worms infect the human brain, and sometimes eyes or lungs. Humans are not a primary host for the parasitic worms, and they eventually die. Nevertheless, they can cause severe illness, and there is currently no effective treatment.

In 1955 the predatory rosy wolfsnail (Euglandina rosea) was introduced to prey on the African snail. It turned out that the rosy wolfsnail preferred to eat the native Hawaiian snails. The African snail population was not impacted in a significant way.

The African snails are nocturnal, and can be found hiding under leaf litter or in thick patches of weeds like devil weed. The devil weed (Chromolaena odorata) can be identified by its three pronged pitchfork shaped pattern of veins on the leaves. This highly invasive weed can grow to 6 feet (2 m) tall and produce up to 800,000 wind-dispersed seeds. It forms thickets that smother other plants. They also release allelopathic chemicals into the soil that prevent other plants from growing nearby. It’s highly flammable too.

Although the devil weed is known to cause allergic reactions, it is widely used in herbal medicine. The leaves are crushed and mixed with other herbs and applied to wounds to stop bleeding and speed healing. Research is being done into its anti-cancer properties.