Common toads (and less commonly other amphibians) are sometimes parasitized by larvae of the toad fly (Lucilia bufonivora), and possibly by other species of fly. The adult fly lays its eggs on the toad, which then hatch out and migrate inside the toad via the nostrils. The larvae then complete their development by feeding on the living tissues of the toad. This process, and the blocking of the toad’s airways, invariably results in the toad’s death.

Adult common toad with toad fly infestation, showing slightly enlarged nostril and toad fly eggs attached to flank.

Toad fly infestation is only rarely observed in the UK but seems to be common in some areas. It can be observed from May to September with most reports in July and August; adults and occasionally sub-adults are affected. Toads infested with toad fly can be readily detected by characteristic “clucking”, enlarged nostrils, and signs of fly larvae in the nostrils (small, white maggots). As the infestation develops, the toad becomes progressively less mobile and finally dies.

Whilst many people understandably find toad fly infestation unpleasant and even upsetting, it is perhaps best to bear in mind that the toad fly is a natural parasite of amphibians in the UK. There is currently no indication that it is a conservation concern – that is, it does not appear to threaten toad populations, though further research would be useful. There is no known prevention or treatment for toads suffering from toad fly infestation. The toad fly itself is an obligate parasite of amphibians, i.e. it can only complete its lifecycle by parasitizing amphibians.

People can help by reporting cases of toad fly to the Garden Wildlife Health initiative: www.gardenwildlifehealth.org. This will help us to learn more about where it occurs and the number of toads affected. This will improve our understanding of the condition, and the extent to which it may affect toad populations.

This video shows a toad infested with toad fly.
Please note: the video contains images some may find unpleasant.

Sources of further information on toad fly:

Garden Wildlife Health - Toad fly (Lucilia bufonivora)

Arias-Robledo G, Wall R, Szpila K, Shpeley D, Whitworth T, Stark T, King RA, Stevens JR (2019) Ecological and geographical speciation in Lucilia bufonivora: The evolution of amphibian obligate parasitism. International Journal for Parasitology: Parasites and Wildlife, 10:218-230. [Available at: www.doi.org/10.1016/j.ijppaw.2019.09.005] 

van Diepenbeek, A & Huijbregts, H (2011). De pad en zijn kwelgeest. RAVON 41, September 2011, Jaargang 13, Nummer 3, p 64-70. [Available at: www.ravon.nl/Portals/2/Bestanden/Publicaties/Tijdschrift/RAVON2011013003.pdf] 

Weddeling K, Kordges T (2008) Lucilia bufonivora-Befall (Myiasis) bei Amphibien in Nordrhein-Westfalen–Verbreitung, Wirtsarten, Ökologie und Phänologie. Zeitschrift für Feldherpetologie 15:183-202. [Available at: http://www.weddeling.info/05-Weddeling_&_Kordges.pdf]