Beneath the sand: a hidden microbial world in antlion traps

In a recent study, we explored the microbiota of antlion larvae, those small, pit-building predators that sit buried in sand and wait for ants to fall into their traps. These larvae live in harsh, nutrient-poor environments, sometimes for years. Yet, almost nothing was known about the microbes associated with them. So we asked a simple question: what kind of microbial communities exist inside these animals, and how do they change as the larvae grow?

A graphical abstract for the study recently published in Ecological Entomology. Credit: W. Antoł.

To answer this, we studied two species of antlions living side by side in sandy habitats but under different environmental conditions. One species (Myrmeleon bore) prefers open, sun-exposed areas with strong temperature fluctuations, while the other (Euroleon nostras) inhabits more shaded, stable environments. We collected larvae at different developmental stages and used DNA sequencing to identify the bacteria associated with them.

What we found was both expected and surprising.

First, antlion larvae do carry bacteria, but not in the way we might expect from other animals. Their microbiota appears relatively simple and highly variable. In fact, there was no clear “core microbiota” shared across individuals or species. Instead, most of the bacteria we detected seemed to reflect the environment: sand, prey, and surrounding conditions, rather than stable, long-term symbionts.

At the same time, we did find patterns. The two species differed slightly in microbial diversity, and these differences likely reflect their contrasting habitats. The species living in more variable, exposed environments showed somewhat higher diversity and stronger shifts across development. This suggests that environmental input (temperature, substrate, prey) plays a role in shaping microbial communities. We also observed changes across life stages. As larvae developed, their microbial diversity tended to decrease, particularly between the second and third instar. This could indicate a gradual stabilization of the microbial community or simply a reduction in transient microbes as the larvae grow and their physiology changes.

What does this mean? Antlion larvae may represent a system where microbiota are largely shaped by the environment, rather than by strong host control. This raises broader questions. If some animals rely heavily on stable microbial partners, while others host mostly transient communities, what determines this difference? Is it diet, physiology, habitat, or some combination of these? And how often do we assume stable symbiosis where there is none? To answer these questions, we need to go beyond identifying which microbes are present and start asking what they actually do. Future work could use metagenomics, transcriptomics, or experimental manipulations to test whether these microbes contribute to digestion, defense, or nutrient cycling, or whether they are simply passing through.

Find out more in our Ecological Entomology article, here.