Ágnes Turóci and Barna Páll-Gergely, two researchers of the ELKH Centre for Agricultural Research (NÖVI) Department of Zoology, have performed a two-year survey on local slug fauna. During their research, they identified two species of slug not yet reported in Hungary. The black-headed slug (Krynickillus melanocephalus Kaleniczenko, 1851) and the keeled slug (Tandonia kusceri (Wagner, 1931)) are both rapidly spreading invasive species that are already widespread in Hungary.

‘Pig’ slug (top) and black-headed slug (bottom). Both scales represent 1 cm. Photographs: Ágnes Turóci.

While snails have been studied extensively, slugs have remained largely ignored in the fields of taxonomy and faunology. The main reason for this is that slugs can often only be identified by dissection and samples preserved in alcohol are much more difficult to handle than collections of dry snail shells. As a result, not much scientific literature is available about how slugs found in Hungary spread, possibilities for their identification, and the damage they cause to agriculture and horticulture.

This agriculturally significant group is part of a larger two-year survey by NÖVI researchers, during which they conducted an intensive, country-wide collection of local slug specimens. Collecting data and samples by successfully employing the citizen science method, namely through Facebook, they were able to introduce the two previously unknown slug species in Hungary in their recently published academic articles. Even though they were only recently identified in Hungary, these species have already become widespread, mostly in areas near towns and cities. Both species are currently spreading and belong to families whose species are considered horticultural pests.

The black-headed slug is 4-6 cm long and is easily identified by its whitish body and black nape and head. Originating from Asia Minor, the Caucasus and Crimean Peninsula, as well as areas of the Black Sea coastal regions, it has in recent years been spotted in Sweden, Ukraine, Germany and Lithuania. The other species, known as the ‘pig’ slug in Hungarian due to it’s thick-set, pinkish body, has a clearly recognizable keel running along the whole of its body from the tail to the mantle edge. They can reach lengths of 8-10 cm when extended. The pinkish-brown body is covered with a darker reticulate pattern that varies in intensity. Native to the Balkan region (Serbia, Macedonia, Northeastern Greece, Bulgaria and Southern Romania), it has in recent years been documented in Ukraine, North American and Slovakia.

There is no data as yet on damage caused by these species in Hungary. Latvia is the only country to publish documentation on the black-headed slug and the damage it causes to pumpkin crops to date.

Though how they spread is still not fully known, but considering their low active range, human intervention probably plays a major role in their expansion. Slugs and their eggs can easily survive being transported in potting soil for long durations, so horticultural and agricultural cargo may have had a considerable effect on the spread of slug species across continents in recent decades. This suggests that the Hungarian slug population is being altered and it is therefore important that the spread of non-native species is continually monitored.