# Spanish fly (disambiguation)
**Spanish fly** most commonly refers to *Lytta vesicatoria* (Linnaeus, 1758), an emerald-green blister beetle of the family Meloidae native to southern Europe, and by extension the toxic substance cantharidin extracted from it and the powdered drug prepared from dried beetles.[1](https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=404363) • [2](https://www.poison.org/articles/blister-beetles-do-not-touch-194) The name is misleading in two ways: the insect is a beetle, not a fly, and it is not only from Spain.[2](https://www.poison.org/articles/blister-beetles-do-not-touch-194)
| Term | Refers to |
|---|---|
| Spanish fly (beetle) | *Lytta vesicatoria* (Linnaeus, 1758), species rank, family Meloidae, genus *Lytta*; GenBank common name "Spanish fly"[1](https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=404363) • [3](https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=114404) |
| Eurasian Spanishfly | An alternate common name for the same species, *Lytta vesicatoria*[4](https://ask.ifas.ufl.edu/publication/IN323) |
| Cantharidin | A colorless, odorless toxic tricyclic monoterpene, formula \( C_{10}H_{12}O_{4} \), produced by blister beetles and the active principle of Spanish fly[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC12487651/) • [2](https://www.poison.org/articles/blister-beetles-do-not-touch-194) |
| Cantharides | A crude drug made by grinding dried blister beetles, historically sourced chiefly from *Lytta vesicatoria*[6](https://www.ideals.illinois.edu/items/27385/bitstreams/92705/data.pdf) |
| Spanish fly (aphrodisiac) | Preparations sold or taken for a purported sexual effect, a use that is groundless and can be fatal[2](https://www.poison.org/articles/blister-beetles-do-not-touch-194) |
| Blister Beetle | A common name recorded for the same species in British species checklists, alongside "Spanish Fly"[7](https://www.nhm.ac.uk/our-science/data/uk-species/taxon?tvk=NBNSYS0000170869) |
## The beetle
*Lytta vesicatoria* is a species of blister beetle placed in the subfamily Meloinae and the genus *Lytta* Fabricius, 1775.[1](https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=404363) • [3](https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=114404) The Natural History Museum's species dictionary records "Spanish Fly" as the accepted English common name, with "Blister Beetle" listed as a junior synonym name for the same taxon.[7](https://www.nhm.ac.uk/our-science/data/uk-species/taxon?tvk=NBNSYS0000170869) The University of Florida's extension literature calls it the "Eurasian Spanishfly" and notes it as a source of cantharidin, while observing that other genera, particularly *Mylabris* and *Epicauta*, have been more commonly used for that purpose.[4](https://ask.ifas.ufl.edu/publication/IN323) A 2022 phylogenetic study of the tribe Lyttini restricts that tribe to a set of Holarctic genera including *Lytta*, reflecting the extensive polyphyly found in earlier circumscriptions.[8](https://resjournals.onlinelibrary.wiley.com/doi/10.1111/syen.12547)
## Cantharidin and cantharides
Cantharidin is the blistering agent excreted by blister beetles through their leg joints; it is a colorless, odorless fatty fluid that is toxic on contact.[2](https://www.poison.org/articles/blister-beetles-do-not-touch-194) Chemically it is a stable tricyclic monoterpene with the formula \( C_{10}H_{12}O_{4} \), retaining toxicity even in the remains of dead beetles over extended periods.[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC12487651/) Recorded cantharidin content of adult beetles, by dry weight, ranges from less than 1% to 5.4%.[4](https://ask.ifas.ufl.edu/publication/IN323) Males are the main source of the substance, transferring it to females during copulation, and eggs also contain it, presumably to deter predators.[9](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/lytta-vesicatoria) • [5](https://pmc.ncbi.nlm.nih.gov/articles/PMC12487651/)
For commercial purposes cantharidin has seldom been used pure; instead, dried beetles are ground into a crude drug known as cantharides, of which *Lytta vesicatoria*, called *mouche d'Espagne* in French, was by far the most important source.[6](https://www.ideals.illinois.edu/items/27385/bitstreams/92705/data.pdf) Pure cantharidin was first isolated by the French chemist Pierre Robiquet in 1810.[10](https://www.mcgill.ca/oss/article/health-and-nutrition-you-asked/spanish-fly-really-aphrodisiac)
## The aphrodisiac legend
Spanish fly is notorious for its historical reputation as an aphrodisiac, a use described as groundless and potentially fatal.[2](https://www.poison.org/articles/blister-beetles-do-not-touch-194) When ingested, cantharidin irritates the digestive and urinary tracts, and urethral irritation has been associated with priapism (persistent, often painful erection); the resulting pelvic swelling is the basis of the purported sexual effect.[9](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/lytta-vesicatoria) • [2](https://www.poison.org/articles/blister-beetles-do-not-touch-194) The fatal dose of cantharidin is in the range of 10 to 65 milligrams.[10](https://www.mcgill.ca/oss/article/health-and-nutrition-you-asked/spanish-fly-really-aphrodisiac) In 1962, cantharidin lost its approval from the US Food and Drug Administration, which judged the substance too hazardous and without proven benefit.[2](https://www.poison.org/articles/blister-beetles-do-not-touch-194) Products sold online as "Spanish Fly" are unlikely to contain any cantharidin and are mostly herbal concoctions.[10](https://www.mcgill.ca/oss/article/health-and-nutrition-you-asked/spanish-fly-really-aphrodisiac)
## Legitimate modern uses
Cantharidin remains in medicine as a topical vesicant. In July 2023, YCANTH (a 0.7% topical cantharidin solution) was approved in the United States for the topical treatment of molluscum contagiosum in patients aged 2 years and older; blisters form within 24 to 48 hours and resolve within 4 to 7 days.[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC12487651/) In veterinary toxicology, cantharidin poisoning of livestock, usually through beetles contaminating alfalfa hay, is a recognized hazard, and the toxicity of cantharidin is not diminished by drying or storage.[11](https://www.merckvetmanual.com/toxicology/cantharidin-toxicosis/cantharidin-toxicosis-in-animals) Research also reports antitumor, antibacterial, and insecticidal properties of cantharidin and its derivatives.[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC12487651/)
## References
1. [NCBI Taxonomy Browser: Lytta vesicatoria](https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=404363)
2. [Blister beetles: Do not touch!, Poison Control (National Capital Poison Center)](https://www.poison.org/articles/blister-beetles-do-not-touch-194)
3. [ITIS Report: Lytta vesicatoria (Linnaeus, 1758), TSN 114404](https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=114404)
4. [EENY166/IN323: Blister Beetles (Insecta: Coleoptera: Meloidae), University of Florida IFAS](https://ask.ifas.ufl.edu/publication/IN323)
5. [Cantharidin: a double-edged sword in medicine and toxicology, Frontiers in Pharmacology (2025)](https://pmc.ncbi.nlm.nih.gov/articles/PMC12487651/)
6. [Selander, Bionomics, systematics, and phylogeny of Lytta (Coleoptera, Meloidae)](https://www.ideals.illinois.edu/items/27385/bitstreams/92705/data.pdf)
7. [Species Dictionary: Spanish Fly, Natural History Museum, London](https://www.nhm.ac.uk/our-science/data/uk-species/taxon?tvk=NBNSYS0000170869)
8. [Multigene phylogeny of blister beetles reveals extensive polyphyly of the tribe Lyttini, Systematic Entomology (2022)](https://resjournals.onlinelibrary.wiley.com/doi/10.1111/syen.12547)
9. [Lytta vesicatoria, ScienceDirect Topics overview](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/lytta-vesicatoria)
10. [Is "Spanish Fly" really an aphrodisiac?, McGill Office for Science and Society](https://www.mcgill.ca/oss/article/health-and-nutrition-you-asked/spanish-fly-really-aphrodisiac)
11. [Cantharidin Toxicosis in Animals, Merck Veterinary Manual](https://www.merckvetmanual.com/toxicology/cantharidin-toxicosis/cantharidin-toxicosis-in-animals)
---
*Topic: Encyclopedia › Life and health › Animals › Invertebrates › Arthropods › Insects › Beetles › Other beetle families (residual lineages)*
*Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 21, 2026 · Edited: Sep 30, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license