Meet Arion vulgaris, the Spanish slug, considered among the 100 worst alien species in Europe. First identified in Belgium in 1973, recent mild winters and wet summers have caused an explosion in their numbers. With the rain this year the gardens in Brussels are overrun with Spanish slugs.
While most gardeners can accept a level of slug and snail damage in the garden, these new invaders are resistant to poisons, have huge appetites and breed individually producing over 400 young per year. They easily out compete native species and very quickly take over a garden.
Rumoured to originate in Northern Spain, the Spanish slug is now present across Europe and increasing in number. They are extremely difficult to deal with, producing a thick sticky mucus when handled. Dropping the individuals into boiling water does kill them, turning the water yellow (nasty).
Unfortunately, because of their high reproduction rate such defence strategies seem pointless. Instead gardeners are encouraged to explore closed off crop protection systems or invest in ducks. It is not known if chickens or fish will eat them as their mucus defence is formidable.
Short of an extreme frost this winter which would reduce their numbers, gardeners will have to explore new defensive measures such as the Hanover slug fence successfully tested in Germany and the UK over the last two years. The Spanish slug is a major threat to local gardens.