Entomology Department Chair Evan Economo Answers Questions About Ants and Biodiversity

The College of Computer, Mathematical, and Natural Sciences hosted a Reddit Ask-Me-Anything spotlighting research on biodiversity.

University of Maryland Entomology Department Chair and Professor Evan Economo participated in an Ask-Me-Anything (AMA) user-led discussion on Reddit to answer questions about ants and biodiversity on November 20, 2024.

Economo’s research combines traditional field and collections-based approaches with emerging technologies in informatics, imaging, sequencing and data science to explore global biodiversity. His research includes biodiversity discovery ("dragon" ants), the evolution of complex traits such as the mousetrap-like jaws of "trap-jaw" ants, and the reconstruction of a global map of ant diversity. 

This Reddit AMA has been edited for length and clarity.

Of all the species you could have picked for studying evolution, why ants?

I wasn’t the stereotypical kid who was fascinated by insects, and later made it my career. I only got interested in ants and insects after I was already in university and became fascinated by the theoretical questions of biodiversity.  Ants first really caught my attention when I was an undergrad, I got a job working as a field assistant in South America for someone researching antbirds, which are birds that follow army ant swarms and catch insects that are running away from them. So I was in the Amazon following around army ant swarms and having adventures all summer, and I got more interested in the ants than the birds.

I primarily study ants because they are a good model system for evolution, ecology, and biodiversity.  They are good models for that because they are diverse, but not too diverse to be tractable.  There are roughly 15,000 species and subspecies, which is a manageable number, whereas some other groups have hundreds of thousands or millions of species.  Moreover, they have many amazing behavioral and ecological adaptations, they have evolved armies, to agriculture, to complicated symbioses with plants and other organisms.  Many of these adaptations are possible due to their complex social organization and division of labor, which is pretty rare in the animal kingdom and another reason scientists are interested in them. 

Another reason is they are a big part of our world.  They are one of the most ubiquitous and abundant animals in terrestrial ecosystems, driving many ecosystem processes.  A small number of species also have become big problems, moving around the world as stowaways in human commerce.  Some of these become invasive and do billions of dollars of damage (for example, fire ants).  So this is an applied reason to care about them, because they are doing harm to both human society and are bad for conserving biodiversity.

Have you heard of ant research about the preferred movements of ants? They look quite organized to me, but it could also be random. Do ants even have a concept of left/right/forward/reverse?

This doesn’t apply to all ants, but ant “traffic control” becomes a big issue for species that move en masse, such as army ant swarms that move lots of individuals and materiel to and from the nest.  This has been studied a fair bit by different researchers.  The current thinking is that the organization of ant movements is self-organized from the interaction rules of individual ants.  So there is no director or instructor telling each ant what to do and where to go.  Ants respond to different stimuli, what they sense in the environment and what they perceive their nestmates doing, which leads them to change what they are doing.  The amazing thing is that through simple interactions, complex colony-level behavior can emerge without top-down control.  I am not aware of anything as simple as right-left rules, but traffic lanes definitely self-organize from these kinds of rules.

Incidentally, this is one of the things sci-fi movies and books usually get wrong.  There have been many alien species that are modeled off of social insects, just two off the top of my head are Ender’s Game and Starship Troopers.  However, in these, the queen is always the mastermind that controls all the others, once the humans manage to kill her, everyone else drops dead instantly.  That isn’t how it works.  Social insect colonies are more decentralized in their behavior, which is almost scarier.

When complex traits evolve, is there a sequence of stable states/plateaus of intermediate forms, or is it more of a huge variety of statistical drunken walks of mutation until a complex beneficial trait gives a strong advantage?

That is the kind of question we are trying to answer in evolutionary biology.  Are complex traits always reached with incremental steps that are themselves viable phenotypes?  Or do you get large jumps with a new complex trait happening spontaneously but rarely?  I think it is a mix of both, but we want to understand when and why different types of evolutionary innovation occur.

Are any extinct ants that had some cool feature that no longer exists?

Oh yes. Extinct ants are incredible and have traits not present in modern ants.  One example immediately comes to mind: there is an extinct group of ants colloquially called “Hell Ants” (Haidomyrmecinae), that have amazing mandible designs that are not found in any modern ants. It is very interesting to ask why these structures that were apparently helpful in catching prey 100 million years ago but not useful for any of the 15,000 species living today.

Have you noticed evolution occurring at a faster pace to match our changing world? Or is the biota falling behind, leaving us with less biodiversity?

Evolution is definitely happening, in particular as species adapt to new habitats such as cities, and as direct responses to human pressures.  One example is elephant tusks evolving to get smaller in response to poaching pressure.  It stands to reason that it is happening faster than normal, although I am not sure I recall measurements of this.  Some of the fastest evolution comes from our artificial breeding of species.  For example, dogs, a single species, have a huge amount of skull diversity.  Typically one would need the diversification of many species over millions of years to cover that kind of diversity.

That said, while some species can adapt to the human world, most cannot live outside native habitats and cope with human pressures.  We know this because many species have gone extinct, far above normal extinction rates, and many more species are likely imperiled that we have not studied well enough.  So I don’t anticipate that evolution will “save” enough species to avert the ongoing biodiversity crisis—we need to reduce our impacts by reducing emissions, protecting wild areas, slowing habitat degradation, and living more sustainably.

What kinds of things have ant pincers evolved to do? Do ants uproot plants for food?

Ant mandibles are incredibly diverse and have evolved to perform many specialized functions. For example, they can be weapons, such as the trap-jaw ants that generate incredible speeds. Trap-jaw ant mandibles can close 5,000 times faster than the blink of an eye and accelerate at over a million G's. Our lab has studied these a fair bit, but we are also interested in mandibles more generally. Here's a video about these ants that's a bit more fun.

Other ant mandibles can be adapted for cutting leaves, grinding seeds, shaving the hairs off millipedes, and so on.

As far as I know, ants don't uproot plants for food, but they can eat seeds, leaf cutters cut leaves and use them to grow fungus. Many ants tend other insects that suck the sap of plants, such as aphids.

Do ant colonies have a natural instinct to breed in favorable traits?

Ant reproductive systems are complex and vary across species, but in the most common case, queens mate and are inseminated before starting a colony, and store sperm from the same male for the whole life.  So workers are not “bred” in the same way we would breed livestock.  The colony reproduces when the queen produces new queens and males.  With that said, there are often mechanisms that prevent workers from going rogue and reproducing themselves.  Colonies will “police” and kill workers that lay eggs, which is one way that social insects discourage selfishness from evolving and destroying the cooperative structure of the colony.  In social insects there is always a tension between cooperative and selfish behaviors, just like in human societies.

What is your favorite modern evolution trait a species of ant has adopted to survive in a more human-centric world from a more "natural" state?

One of the most spectacular changes that we’ve seen in some ants in the modern world is the phenomenon of “supercolonies.”  Normally, ant colonies distinguish nestmates from neighboring colonies.  In some species that have invaded new areas, such as the Argentine ant, have lost this recognition. So most of the Argentine ants in Europe are essentially a single colony, you can pick up an ant in Spain and drop it in Germany and it will just join the nearest colony and go about its business.

Have you seen any evidence of rapid adaptations due to climate change in arthropods? 

Insects are adapting to climate change in many different ways. One prominent example of climate-related disruption is the Monarch butterfly migration, which depends on different climatic cues at different stages and the butterflies’ ability to find host plants along the way. When climate changes, this can mess with these cues and disrupt the whole cycle. 

Many other adaptations have been documented, from insects changing color to be lighter (and not heat up) to shifting of species ranges northward.  How fast evolution can happen depends on how much heritable variation there is in the population already.  If there are already variants that are adapted to the new conditions it can happen quickly.  If complex genetic changes are needed it could take thousands of years and be too late.  We don’t really have a general understanding of what will happen to most species, this is why it is an intensive area of research.