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Wasps Got Into Your Tree? Why Wasps Strip the Bark from Trees

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Autumn is approaching in Australia. This means that owners of trees favoured by European hornets and wasps need to look out for the usual late summer/early autumn feast. If enough European hornets (Vespa crabro) or European wasps (Vespula Germanica attack the same tree or bush, they can do some serious damage.

But why do they do it?

It Is Their Last Feast 

During the spring and summer, wasps and hornets collect insects to help feed the young of their quickly expanding nest. However, once late summer arrives in Australia, hornet and wasp workers change their tactics. No longer do they collect for the young. The queen is preparing to go into hibernation and so is no longer laying eggs.

For the next few weeks then, European wasps and hornets will gorge themselves on tree sap. They don't choose just any old tree, however. The sweeter the tree is, the more delicious their last meal will be. Afterwards, many of these worker wasps will die due to the colder temperatures. However, in mild winters, an entire nest could survive.

Sweet Trees and Bushes Are the Targets

European hornets and wasps develop a sweet tooth for their final feast. This means the sweeter the tree or bush, the better the feast. If your tree or bush has become the target of European wasps or hornets each year, it is probably one of the following species:

  • River Birch
  • Lime 
  • Maple
  • Poplar
  • Rhododendron
  • Aspen
  • Lilac bush
  • Rosebush

This isn't an exhaustive list. However, if wasps are attracted to your tree each year, whatever it is, it most likely produces many flowers and is sweet.

Can Wasps or Hornets Kill a Tree?

If a particularly large nest of hornets or wasps locates a nearby tree that is suitably sweet enough, they could cause serious damage. As they chew through the bark of trees, often in large numbers since they are no longer required to work in the nest, European wasps or hornets can girdle a branch or even the main leader of a tree.

Because wasps and hornets chew through a tree's bark to get to the sweet sap beneath, they could end up injuring or even killing a tree. For instance, if these feasting insects remove an entire ring of bark from a branch, that branch will die. While this might not kill the tree, it will hinder its ability to take in food because fewer branches mean less photosynthesis.

These insects also attack the trunk or the main stem if they are able to gain access. If this happens, the tree could starve and die since, without its bark, it can no longer transport food, and it is now open to diseases and pests.

Has your tree suffered wasp or hornet damage? Hire a tree lopping service to assess the damage. If you need to remove the tree, ensure also that you remove the wasp's nest before planting another sweet-sapped tree in the area.