Researchers have discovered and described six new species of ants belonging to the genus Prionopelta.
Commonly, known as ‘Dracula Ants’ for their unique feeding behavior, these new members of Prionopelta have been found to be tiny, ferocious social predators living in Madagascar.
The research conducted on these ants is part of an ongoing effort to further understand, and educate others about, Malagasy biodiversity.
During a recently concluded study conducted over the last ten years, researchers from the California Academy of Sciences (CAS) working with the Madagascar Biodiversity Center (MBC) have discovered and described six new species of ants belonging to the genus Prionopelta. Commonly, known as ‘Dracula Ants’ for their unique feeding behavior, these new members of Prionopelta have been found to be tiny, ferocious social predators living within the subterranean, microscopic ecosystem of the forest floor soils in Madagascar.
For much of the last decade, members of the MBC, led by entomologist Brian Fisher from CAS conducted extensive sampling across Madagascar’s diverse habitat by sifting forest floor spoils to find the tiny, colorless ants. Malagasy scientists and trainees at the MBC assisted with the research and collected ants throughout the duration of the study as part of an ongoing effort to further understand, and educate others about, Malagasy biodiversity.
Unique Sampling Method
One of the main tools the team used for sample collection is the deceptively simple ‘Winkler’ trap. Organic material is gathered from the forest floor and suspended to dry in a special bag. As the organic material dries out, the natural behavior of insects hiding within is to move downwards with the remaining moisture to the bottom where a collection vial is conveniently located for capture. This technique allows scientific collection and study of extremely difficult to find soil-dwelling invertebrates, such as the tiny Dracula ants. Ants belonging to this genus are minute and colorless, with the smallest, P. laurae, measuring 1.5 millimeters in length and 0.2 millimeters in width.
After sorting through the debris, thousands of ants from the genus Prionopelta were collected, sorted, measured, and analyzed. Six new species were discovered, described, and named. One species was given the name P. vampira, for the single, extremely long mandible ‘tooth’. Another, with delicate patterns on its head, inspired the name P. subtilis, while P. xerosilva is named after the ‘dry forest’ habitat in which the species exclusively resides.
Wolves of the Microscopic World
Members of the ant genus Prionopelta are described by researchers as social predators, and differ from other ant colonies in both size and organization. A colony of Prionopelta spp, typically consist of hundreds of workers, rather than millions, and has a less complex social structure in comparison to other species. Prionopelta, and all other Dracula ants (Amblyoponines), have a loose social structure where they live together and coordinate behavior. It is a simple social organization with a queen caste similar in appearance and behavior to workers.
“Painfully little is known about these ants and their behavior, life history, and role in the ecosystem,” explains Rick Overson, who assisted with sorting all the material and describing all the new species. “If we were to speculate, the few species widespread in Madagascar are specialist, group hunters. From a food ecology standpoint, they occupy the niche of being ‘wolves’ of sorts’”.
An investigation of their behavior led by Bert Hoelldobler of Germany’s Theodor Boveri Institut, found that Dracula ants send chemical signals to one another regarding the location of food sources by laying down a secretion from a gland in their legs. This behavior is then followed by a body-shake to attract other ants who then follow the ant that initiated the behavior.
It is the way in which Dracula ants survive in times of limited resources that they differ widely from other social ants. The species was dubbed with its morbid name due to a practice of wounding the young of their colony and drinking their blood. This behavior is described as ‘larval hemolymph’ and can be considered a form of resource sharing.
Overson explains, “Some ants have the ability to store nutrients in a special section of their digestive tract. With the help of a specialized structure, the proventriculus, the stored nutrients are used to provide food to another colony member in need. Dracula ants lack this mechanism and have developed an alternative form of resource sharing by using the larval hemolymph system.” One experiment showed that the practice of larval hemolymph increases when prey is scarce, while the behavior is suppressed when food is abundant.
For researchers like Rick Overson and Brian Fisher, Madagascar is a rich ground for the study of ants, with 418 documented species found there; 379 of these are endemic to the island and found nowhere else on earth, making Madagascar an important and unique laboratory for understanding ant behavior and evolution.
Overson R & Fisher BL (2015) Taxonomic revision of the genus Prionopelta (Hymenoptera, Formicidae) in the Malagasy region. Zookeys 507: 115-150.