Caterpillars lack a resident gut microbiome

Significance Microorganisms residing within animal tissues as symbionts can be critically important to many aspects of animal biology. For example, the microbiomes of many insects, such as aphids, honeybees, and termites, can provide nutrients, deter pathogens, and help digest food. We examined whether caterpillars also engage in intimate microbial partnerships. Across a broad diversity of caterpillar species, we found that microbes in the gut are extremely low-abundance and predominantly leaf-derived, suggesting their transient nature. Furthermore, suppressing bacteria in tobacco hornworms ( Manduca sexta ) had no detectable effect on caterpillar growth or survival. With caterpillars as a prominent—but possibly not unique—example of relative autonomy, the degree of reliance on microbes is an underappreciated yet likely important dimension of animal biodiversity.