Rasopone ferruginea, a member of the ant genus Rasopone. These ants creep around underground or deep in rotten wood. The species don’t vary much morphologically, but a combination of DNA data and subtle morphological differences reveal many species distributed throughout the Neotropics. (Photo by John Longino, Ph.D., via AntWeb, CC BY 4.0)

By Paige Embry

Paige Embry

Tramp into a wet tropical forest to look for ants and you’ll miss most of them, because about two-thirds of the ant diversity in those forests is out of sight, living in leaf litter and rotten wood. The best way to discover these ants is to sift large quantities of the debris that they call home.

After a day of wandering and sifting, John Longino, Ph.D., professor of biology at the University of Utah, says you end up “with a little bag of gold.” Longino and Michael Branstetter, research entomologist at the U.S. Department of Agriculture’s Agricultural Research Service, have coauthored a paper published in April in Insect Systematics and Diversity on how they developed a “bird guide” style identification system for some of the “gold” found in those bags, ants in the genus Rasopone.

John Longino, Ph.D.

Longino and Branstetter used specific DNA sequences that are conserved within the ants’ genome to develop a phylogenetic tree that shows the evolutionary relationship among Rasopone ants. With that genetic information, Longino says “we went from maybe three to 30 species.” The next step was to devise a method for identifying the species without using advanced lab techniques. Historically, that would mean creating a dichotomous key, but for the Rasopone they decided to take a different route.

Anyone that has used a dichotomous key knows the frustrations, and occasional triumphs, they offer. Here’s the opening couplet from the Key to Neotropical Ponerinae Genera, the sub-family that includes the Rasopone:

1. Mandibles long and linear, inserted in the medial anterior portion of the head, semiparallel when closed and forming 180 degrees when open …..2
2. Mandibles otherwise, inserted in the lateral anterior portion of the head, never semiparallel when closed and forming 180 degrees when open …..3⁠

And that’s just to get the genus.

Longino says that keys are great learning tools because they teach you what you should be looking at, but when you get down to the species levels they often make identification harder. For the Rasopone he notes that you may see several recognizable species in one area and a similar looking group 200 kilometers away, but “it’s really hard to match those up with the ones at your first site, and you get fooled.” Relying just on morphology, Longino says, “failed miserably. The species were right locally but they were completely off-base when you covered the whole geographic range.”

John Longino, Ph.D. (left), and Michael Branstetter, Ph.D., pose at a field site in Costa Rica, surrounded by lea litter-sifting equipment. Prior to litter-sifting methods, the ant genus Rasopone was known from only a handful of specimens. Large biodiversity inventory projects, with student teams sifting litter throughout Central America, produced nearly 800 specimens. Branstetter and Longino’s study on the genus, published in April 2020 in Insect Systematics and Diversity, would have been impossible without those projects. (Photo courtesy of John Longino, Ph.D.)

So, when it was time to devise an identifications system, Longino and Branstetter thought, “Why pound our heads against trying to make a dichotomous key of these things?” Instead, they decided to use the “bird guide” method that couples geographic locations of particular species with key identifiers and photos.

For those of us who have carefully and laboriously keyed our way to the wrong species, a different approach is greatly appreciated. Longino says that he tries to make his entomology students key out insects, but they tend to go looking at places like Bug Guide instead. He admits that he keeps the information in his head in a similar way. For the Rasopone, if he has the size and location for an ant, he only has to mentally sort through a handful of species rather than all 30.

An example of the “bird guide” identification tool for the ant genus Rasopone developed by researchers Michael Branstetter, Ph.D., and John Longino, Ph.D. Shown here are a distribution map, face view, and lateral view of the petiole of Rasopone pluviselva, R. minuta, and yet-to-be-named species R. JTL043 and R. JTL048. On the maps, red dots are sites with genetic sequence data. Red boxes are type locality. (Image originally published in Longino and Branstetter 2020, Insect Systematics and Diversity)

Maybe this method, defining the species via the genetic information and then using the “bird guide” approach, is the next logical step for insect identification—one that more people will find easy to use. ‘Once you have resources that allow people to identify things,” says Longino, “it attracts people. … Creating these tools can create a user group around them.”  Even, perhaps, for an obscure group of leaf-litter ants.

Longino thinks that once a “little pocket analyzer” comes along that lets you stick an insect leg in and match it up with a database, the dichotomous key will be dead—and presumably the “bird guide” method as well. He doesn’t, however, think that such a tool would mean the end for taxonomists.

He says most people want to know more than just the name of something; they want to understand what is behind the name, where that organism fits into the world. Taxonomists are the keepers of that “deep natural history.” Also, taxonomists help provide a map to the living world, and Longino thinks we need to make that map as detailed as possible right now, “because things are changing so quickly here at the beginning of the Anthropocene. This is the last chance to see the remnants of a pre-Anthropocene world. … We should have a sense of them all, and now is the time to do it.”

Paige Embry is a freelance science writer based in Seattle and author of Our Native Bees: North America’s Endangered Pollinators and the Fight to Save Them. Website: www.paigeembry.com.