A study published in Myrmecological News reveals new details about the larval stages of three species of trap-jaw ants. The 292 scanning electron microscopy images collected in the study, such as the one above showing the head and mouthparts of a first-instar Odontomachus brunneus, are freely available online. (Photo credit: Eduardo Fox, Daniel Solis, Adrian Smith, Joshua Gibson, CC BY 4.0)

By Adrian Smith, Ph.D.

Trap-jaw ants, with their spring-loaded jaws and powerful stings, are among the fiercest insect predators, but they begin their lives as spiny, hairy, fleshy blobs hanging from the ceiling and walls of an underground nest.

New research provides the first detailed descriptions of the larval developmental stages of three species of Odontomachus trap-jaw ants. This work was done by scientists at North Carolina State University & the North Carolina Museum of Natural Science, South China Agricultural University, Sao Paulo State University, and University of Illinois and published in the journal Myrmecological News.

While there are nearly 16,000 described species of ants, less than half of 1 percent of those have had their developmental stages, from egg to adult, described. The number of larval stages of insects is variable, however this study found that workers of the three trap-jaw ant species studied go through three stages of larval development.

The researchers determined the number of larval developmental stages, also called “instars,” through measuring hundreds of larval head widths and body lengths and through identifying stage-specific anatomical features through scanning electron microscopy (SEM).

The SEM images revealed an amazing complexity of body parts such as four “sticky doorknobs” on the backs of first and second instars, used to adhere the larvae to nest walls and ceilings, complex “frustrum with spire” hairs of second and third instars, and silk-spinning “pseudopalps” of third instar larva. (All 292 original electron microscope images are freely available through CC BY 4.0 license.).

Beyond providing the first categorization of larval stages for these ants, surprising results from the work include discovery of the “sticky doorknobs,” which were previously studied in only one other ant species, developmental anomalies such as the appearance of additional doorknob protuberances, and the discovery of a larval parasite found in the gut of a third instar larva.

This research provides foundational knowledge that enables future research questions on developmental trajectories, such as when an individual might switch from a developing into a worker to developing into a queen. Beyond furthering our understanding of these social insects, the researchers hope the images will inspire interest and appreciation for the complexities of these organisms.

Adrian Smith, Ph.D., is head of the Evolutionary Biology & Behavior Research Lab at the North Carolina Museum of Natural Sciences’ Nature Research Center and a research assistant professor in the Department of Biological Sciences at North Carolina State University. Website: www.adrianalansmith.com. Email: aasmith7@ncsu.edu