The box tree moth, a small butterfly from East Asia, has been spreading since 2007, especially in southern Germany and the neighboring countries, and has already destroyed thousands of valuable stocks. But now nature seems to be fighting back - the first birds and wasps have been observed eating the protein-rich caterpillars and even feeding them to their offspring.
Birds like to eat the box tree moth
No natural predators
The voracious pest was originally introduced to Europe via imports from Asia and spread quickly. As is usual with many neozoa (i.e. invasive species), the local wildlife initially had no use for the moths. Hobby gardeners also reported that they had observed birds trying the caterpillars, but they finally regurgitated the pest again. Therefore, it was initially assumed that the caterpillars absorbed and stored the bitter toxins of the boxwood. Thus, they also tasted bitter to the birds and were inedible for them. In fact, laboratory studies found that the caterpillars stored the same toxins in their bodies as boxwood. Some of them were merely stored, others even digested and thus used as a source of food.
The local wildlife gets a taste
In the meantime, the plague seems to be slowly dying down, which is probably also due to the fact that many gardeners have removed boxwood from their gardens out of desperation and the pests that specialize in boxwood can no longer find any food. On the other hand, the local bird life seems to be slowly getting a taste for it: for many songbird species, the larvae of the box tree moth are now part of the menu. Apparently there was a phase of getting used to it, after which even the toxins no longer seem to bother sparrows, great tits and other feathered pest controllers.
Easy prey for sparrows
Especially sparrows have discovered the green caterpillars as easy to catch, extremely numerous (hundreds to thousands of butterfly caterpillars cavort on some bushes) and protein-rich food for their chicks. Many a gardener has already observed how the small birds lay in wait in the boxwood bushes and literally searched the plantings for an infestation with borer caterpillars. Not only sparrows, but also other songbirds and garden birds such as great tits, chaffinches and redstarts have discovered the boxwood bush as a worthwhile hunting ground. So make sure that the birds feel comfortable in your garden, for example by hanging up nesting boxes near the boxwood plantations - with a bit of luck, sparrows, tits and Co. will gladly accept the offer and reciprocate by eating the borer caterpillars.
Do not use any chemical substances
A bird-friendly garden also means not using any chemical sprays to combat the box tree moth. These toxins have the unpleasant property of not only poisoning the pest, but also the beneficial insects that are welcome in the garden at the same time. The birds that eat the caterpillars would subsequently die from secondary poisoning. However, since the sparrow population has been declining continuously for years and both the house and tree sparrows have now landed on the early warning list of endangered species, this new source of food for the cute animals might be the chance to recover again. So what can you do for a non-toxic but still effective control of the box tree moth?
Important measures against the box tree moth:
- Attaching numerous nesting boxes (hang up cat and rat safe!)
- Bird feeding in winter (attracts birds)
- Blow out the box trees with a high-pressure cleaner in summer (to get caterpillars out of the bush interior)
- No use of chemical sprays (not even if it says "bee-friendly" on it!)
- instead use of agents with Bacillus thuringiensis
Pollinating the plants with algae lime has also had good results in the past.
tips
In addition to songbirds, wasps now seem to have taken a liking to the fat boxwood caterpillars. So no longer see the animals as annoying visitors at the summer coffee table on the terrace, but also as welcome pest controllers in the garden. They can then have a piece of the sweet cake as a reward.