Frequent infection of urban grass snakes (Natrix natrix) oral cavity with Leptophallus nigrovenosus trematode.

Land disturbances caused by urban development modify and create novel habitats with novel ecological pressures, which in turn may negatively affect remaining wildlife populations, e.g. by altering interspecific interactions. However, it is not clear whether these modified interactions, e.g. parasitism, affect urban wildlife negatively. This is especially true for reptiles, as even parasitism under natural conditions is understudied in this group. We have observed that up to 35% of grass snakes (Natrix natrix) are infected with the trematode Leptophallus nigrovenosus in urban areas of Kraków, while none of snakes sampled in nearby suburban and non-urban forests exhibited this infection. As this trematode typically inhabits the intestine, we suggest that its occurrence in the oral cavity may be a sign of very high infection rates. However, we did not detect any negative effects of observed infection on body size, mass and body condition of affected individuals. On the other hand, competition with other parasite species in suburban and non-urban habitats may be responsible for not detecting L. nigrovenosus in grass snakes from these sites. Nevertheless, interpretation of our findings is difficult, as knowledge on L. nigrovenosus biology is very limited. Our study underlines the necessity to fill the research gap in reptile parasitology.