Swallowtail frass and colon cancer
Back in late 2023, a paper appeared in the journal BMC Genomics (24(1):735; DOI: 10.1186/s12864-023-09841-0) that demonstrated that an extract from the caterpillar frass (faeces) of the Swallowtail butterfly (Papilio machaon) could block the proliferation of colon cancer cells, specifically HCT116 cancer cells.
I must confess I’d not checked in with this research, which is, of course, interesting from the biomedical, pharmaceutical, and lepidopterological perspective, since it first appeared. The researchers point out that insect frass has been used in natural medicine in Asia for a long time, but little is known about the metabolite makeup or actual physiological activity of any of the chemicals found in insect frass.
The theory goes that biochemicals present in the plants the insects eat are most likely to be metabolised by the enzyme cytochrome P450 (CYP) in Papilionidae insects. In the 2023, paper, the team extracted the components of the frass of P. machaon larvae reared on Angelica keiskei, Oenanthe javanica or Foeniculum vulgare and examined the biological activity of each component. The chloroform extract from frass of Swallowtail larvae fed on A. keiskei was the extract that was active against colon cancer cells. The team alludes to the active chemical as being a chalcone.
The team suggested at the time that these compounds might be investigated further as pharmaceuticals for treating colon cancer, although that is a long way off. Perhaps closer is the potential to use the same enzymes used by the larvae to metabolise chemicals from their foodplant to transform other chemicals into novel physiologically active compounds in a biosynthetic approach to chemistry.
A subsequent paper from the team in PLoS ONE (2025 Jul 23;20(7):e0321438; DOI: 10.1371/journal.pone.0321438) discusses more broadly the metabolic ability of Swallowtails and the production of other bioactive substances from plant components in the food they eat.
It is worth reiterating that this kind of biology-meets-chemistry science produces a lot of research papers and has done for decades. The majority are fascinating but sadly only rarely* lead to actual pharmaceutical products and when they do it can be many years from initial discovery to a product reaching the prescribing clinicians. But, who knows, one day we may be taking pills made from extract of larval poo for who knows what kinds of disease?
*That said, an estimated 40 percent of prescription medicines are derived from natural sources!