Crazy Ants

The tawny crazy ant (Nylanderia fulva) has invaded Gulf Coast region in recent years.  First found in Houston in 2002 scattered infestations are now found in all Gulf coast counties extending west as far as the Hill Country. Individual infestations can be huge, spanning kilometers in diameter. This South American species is successful in both natural environments and areas influenced by human presence and disturbance. They develop extremely dense populations where they establish, displacing native ants, many arthropods, and interestingly the imported fire ant that invaded before them. These ants also threaten wildlife more generally. The reduction in the arthropod food base is certain to reduce the success of animals like nesting birds, and through sheer numbers these ants may also directly affect the survival of nestlings. Their invasion of Texas nature preserves designed to protect migrating and endangered birds is particularly alarming.

The Invasive Species Research Lab at BFL is working to understand the basic biology and ecology of this invader and its natural enemies. Our ultimate goal is to develop an effective biological control strategy for this ant in order to limit the expansion and success of this invader in a sustainable manner.  We have made progress on several fronts.

Research Findings

To gain a better understanding of the costs of this invasion, our lab has examined the impact that tawny crazy ants have on native arthropod communities. We have found that they outcompete and displace all of their larger, native ant counterparts in areas that they colonizes. This species also reduces the diversity and abundance of insects generally, critical components of the food web. These losses to biodiversity are greater than the damage done by imported fire ants that occupied these habitats before the crazy ant invasion.

Interestingly, dense populations of invading tawny crazy ants even displace the notoriously tough imported fire ant. Surprisingly, tawny crazy ants can easily kick imported fire ants off of food resources and even take over their mounds to use as their own nests.  We conducted follow-up research to understand how this occurs. We learned that tawny crazy ants possess behavioral and chemical adaptations that allow them to fight fire ants with impunity. Tawny crazy ants, like all ants in this group, produce formic acid as venom and use it as a weapon when fighting other ants. However, by applying their own venom to areas of their body exposed to the highly toxic, alkaloid venom of fire ants, crazy ants can completely detoxify the fire ant venom. This study was the first documentation of this type of chemical counter-measure in insects. It turns out this use of formic acid is shared by many species of ants related to tawny crazy ants and thus has deep evolutionary roots.

Tawny crazy ants are currently restricted to the Gulf Coast region of North America. Although this is partially happenstance, an environmental niche model, done in collaboration with a variety of researchers in North and South America, indicates that this distribution reflects their underlying climate tolerances. The Gulf Coast region is particularly suitable for this ant and it is likely to remain particularly problematic in this region.

We have also undertaken studies into the colony organization in this species. In both their native range in South America and in North America tawny crazy ants have multiple queens per colony. In South America, tawny crazy ants from different colonies are mutually intolerant. This type multicolonial social organization is common in ants. Occasionally, in their native range, colonies become large and span areas of up to 100 meters in diameter. However, in North America, tawny crazy ant workers from different areas of the same infestation, from different infestations, or even from different states display no aggression when brought together, treating each other as nest mates. In fact, behavioral and genetic data gathered to date indicate that all tawny crazy ants in the Southeastern US and Texas are members of the same supercolony. Although local infestations may not be connected to each other, the ants recognize each other as close relatives. Understanding how nests within colonies and colonies within populations interact is crucial piece for any informed social insect management program.   

Progress Towards a Sustainable Control

While tawny crazy ants are formidable, our initial studies of this species have yielded several potential candidate control agents.  As with all modern, responsible biological control efforts, the first priority is to demonstrate that the impacts of the candidate control agents are specific to tawny crazy ants. The first tawny crazy ant pathogen we have encountered is the microsporidian pathogen, Mymecomorba nylanderiae. Our lab, in co-operation with USDA scientists, described this pathogen and documented its presence in crazy ants in scattered populations in Texas and Florida. We do not yet know the how this pathogen got into US tawny crazy ant populations, but we have not found it infecting native ants or other arthropods in nature or in the laboratory.

In the lab, we have demonstrated that this pathogen reduces the developmental success of tawny crazy ant larvae and reduces the lifespan of adult tawny crazy ant workers, with the effect being more dramatic when conditions like drought reduce foraging activity and the availability of sugars. In ongoing studies of infected tawny crazy ant populations in the field, we have documented the decline over several years of many infected populations. We have conducted experimental introductions of this disease into tawny crazy ant infestations in a variety of sites. Learning how to get these inoculations to reliably take is an area of active research. However, in two locations where the disease established, within a few years of establishment, the TCA population collapsed to local extinction. This pathogen is a promising biological control option, but much remains to be learned. 

Phorid flies are another potential control agent for tawny crazy ants. In the past, several species of South American phorid flies were introduced to Texas by our lab to control imported fire ants. These parasitoid flies have proved extremely species-specific, attacking only the imported fire ant.  We have identified two species of phorid flies that attack tawny crazy ants in South America: Pseudacteon convexicauda and a recently discovered, closely related species that is undescribed. We will begin our evaluation of these candidates by confirming that these flies are specific parasites of tawny crazy ants and quantifying the impacts that they have on this invader in its native ecosystems in South America.