Plant Doctor Archive

Slugs on apple tree

LIVING in a rural area we have to protect our fruit trees from marauding opossums and to do this we wrap lightweight tin round the trunk to stop them climbing up, which works fine. This year when we took the tin off to replace it I noticed these odd-looking slugs. Can you tell me more about them?

I FORWARDED your photo to Landcare Research in Canterbury and scientist Gary Barker identified them as the native slug Athoracophorus bitentaculatus which is relatively widespread in both the North and South Islands. There is not a lot written about native slugs, but in a Dominion Post article in March this year Dr David Burton of Victoria University's school of biological sciences is quoted as saying, "Native slugs don't eat cabbages. They eat encrusted algae on leaves. Once you start to look at them they're unique. There's nothing in the world like them. They prefer living inside rotten logs where they can get away from predators such as weka."

So your apple tree slug isn't doing the tree any harm - it's enjoying the nice atmosphere you've created under the tin possum deterrent. Like the pesky introduced slugs which cause havoc in our gardens, the native ones are hermaphrodite, meaning they possess both male and female reproductive organs, though mating with another slug does still take place. They lay around 50-60 eggs and can live for about four years."

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.