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When sand flies are not sucking the blood of mammals, they feed on plants – and it turns out their favorite plant isn’t even legal in most countries. We don't know for sure that sand flies enjoy cannabis’ THC, but it's a likely explanation. Perhaps the little vampires are so persistent because they almost constantly have the munchies.
Much like mosquitoes, sand flies feed mostly on plant sugars, except when the females need the proteins in mammal blood for their eggs to mature. Besides making them exceptionally annoying, the blood-sucking habits of both types of insects have been hijacked by diseases to get from one victim to another. Where mosquitoes carry malaria and dengue fever, among other diseases, sand flies transmit Leishmania – a large family of parasites whose symptoms include skin ulcers, anemia, and liver damage.
Not surprisingly, most of the attention on sand flies' eating habits has been focused on the circumstances in which they bite humans. However, Professor Alon Warburg of the Hebrew University of Jerusalem decided to look at the rest of their diet.
Sand flies like nectar and the honeydew secreted by other plant-sucking insects, but they also bite plant leaves and stems to access phloem sap. Warburg led a team to further investigate their preferred plants.
Rather than trying to track sand flies and watch them feed, Warburg and co-authors designed a tool for sequencing the DNA of the flies' recent meals. They applied this to wild-caught sand flies at seven locations on three continents. In Proceedings of the National Academy of Sciences, the team report that the sand flies often prefer newly introduced plants to native fauna.
More strikingly, many of the flies at six locations carried traces of cannabis DNA. And despite its widespread prohibition, cannabis was only spotted by the researchers at one site, and even there they were rare. Near Tuba on the West Bank, 70 percent of the sand flies studied had been feeding on cannabis.
The paper notes that for most plants, the methods the team used would not distinguish between closely related plant species. However, the gene the researchers focused on varies so much between Cannabis sativa and other species of cannabis that it represents an exception. Consequently, the authors confirm it is good old marijuana the flies are eating, not some related species.
Warburg suggests the discovery could lead to sand fly deterrents. Moreover, since some cannabinoids have antimicrobial activity, there is a possibility cannabis consumption may inhibit Leishmania infections, reducing the chance they will be passed on to a fly's next victim.
More devious minds might ponder if the sand flies' nose for cannabis could be used by police, or thieves, to track down hidden plantations.
