Six new species of a mysterious blood-sucking ant have been identified in Madagascar — and they’re an especially odd bunch.

The so-called Dracula ants, described today (March 31) in the journal ZooKeys, seem to defy many of the normal rules that scientists use to classify ants.

“The genus Mystrium is the most mysterious group within the bizarre Dracula ants,” study co-author Masashi Yoshimura, a researcher at the California Academy of Sciences, said in a statement. “Mystrium was a difficult group to identify because of the remarkable variation within each species.”

Source: Live Science