While collecting thousands of Island Apple Snail (Pomacea insularum) egg clusters from Wellman Pond, we often speculated on what ferocious predator could have elicited such high reproductive capacity in this South American snail through evolutionary time. Initially, we fantasized about some large reptile, maybe a 20’ Snail Anaconda (Eunectes pomaceoraptor?), feeding so effectively on apple snails in the Argentine rivers and marshes that the remaining few adults had better reproduce prolifically for the species to merely survive. Then, as we began to notice the numerous ant bites received while wading through the shoreline plants, it came to us. Maybe, the ferocious predator wasn’t all that large. This notion was solidified when our 4-ton pile of disposed snails became one giant Fire Ant bed!
The Red Imported Fire Ant (Solenopsis invicta) and the exotic Apple Snails (Pomacea canaliculata & P. insularum) have two common traits: They are both highly invasive in the southern U.S. and their native ranges in South America generously overlap. Surely, they co-evolved in a predator-prey relationship with hydrology as a key component. Fire Ants are, indeed, ferocious predators of snails, having caused the extinction of a native tree snail in the Florida Keys (Forys et al, 2001). Stevens et al (1999) documented that Fire Ants attacked native apple snails (P. paludosa) in Florida that became “exposed during dry down conditions.” Yusa (2001) observed that “when egg masses [of P. canaliculata] were experimentallyplaced on levees [infested with Fire Ants], on average 50% of the eggs were lost within two days in March and 38% were lost within threedays in August.No eggs were lost when ants weresuccessfully excluded by water.” Way et al (2009)noted that “periodic drainage . . . enables [the tropical fire ant] to join the predator complex . . . valuable for ant-based control of pests such as snails” in rice paddies.
The current range of the exotic Red Fire Ant in the U.S. encompasses the projected range of the invasive South American Apple Snails. Certainly, predation by the Fire Ant will provide some friction to the rate of expansion of the exotic apple snails in the U.S., especially in areas with fluctuating water levels. Can we take further advantage of this ancient predator-prey relationship? Based on Yusa (2001), Way (2009), and personal observations, it appears a short period of water level manipulation in the presence of red fire ants can have a deleterious effect on apple snail reproduction. When the bases of shoreline plants are exposed in Wellman Pond, for example, numerous Red Fire Ants begin eagerly scouting for egg clusters. I am inclined to ask the Parks personnel not to treat the fire ant mounds there. Periodic, partial “drawdowns” also seem warranted. Let the rematch of invasive Pomacea and the Red Fire Ant continue! Posted by Jess Van Dyke
UF’s Excellent site on Red Fire Ants:
National Geographic video on Fire Ants: