Rated as “top pest” by the Royal Horticultural Society, the box tree caterpillar is a very recent pest in the UK. They first appeared in Europe in 2007, a moth was first spotted here in 2008 and our first caterpillar infestation was in 2011.
What started as a handful of infestations has rapidly escalated to hundreds every year, with London and the south of England particularly hard-hit.
Box tree caterpillars have a voracious appetite and can completely defoliate their host trees within days of hatching. Any sign of a box tree caterpillar infestation needs to be taken seriously and treated rapidly.
Box tree caterpillars are a very classic-looking caterpillar: bright green with a black head and black stripes along their body. As they feed, they cover themselves in a shroud of webbing to hide themselves from predators.
They start life as almost impossible to see larvae just 1-2mm long before growing to a maximum of 3-4cm over around four weeks. Their pupae are covered in web, about 2-3cm long and start green before gradually turning brown.
Adult box tree moths range from solid brown to white with brown edges all the way around the wings. They lay clusters of flat, yellow eggs beneath box tree leaves.
Box tree caterpillars can complete their lifecycle three times in a year from March to October, so you need to remain vigilant and regularly inspect your hedges for any signs of infestation. The moment you spot anything, contact us.
Box tree caterpillars are named after their favourite food: box trees.
Box trees are a popular choice in hedges and topiary, and are found in many of Britain’s historic gardens. These sturdy, slow-growing trees can live for hundreds of years, and have been the preferred hedge tree as they were seen as almost indestructible – until the box tree caterpillar showed up.
In days, an infestation of box-tree caterpillars can suddenly transform beautiful hedges older than me or you into skeletal shrubs shrouded in a veil of webbing. It’s a devastating sight.
Box tree caterpillars are an invasive species native to East Asia.
Back home, their population is kept under control by predatory wasps, which we don’t have here in the UK. Birds – our usual protectors of hedgerows – also won’t eat box tree caterpillars as they’re packed with foul-tasting toxins. Without any natural predators, it’s up to us to control their population.
Gardeners and pest controllers can do our best to tackle infestations as they appear, but there’s no beating a natural ecosystem when it comes to keeping pests in balance. Without that, we can expect the spread of box tree caterpillars to get much worse before it gets better.
For DIY treatment, the best thing you can do is thoroughly inspect your box trees and pick off any caterpillars you find and rub the underside of leaves to remove any eggs.
As box tree caterpillars are not native to UK, there’s a higher than usual risk of allergic reaction both to the caterpillars themselves and their webbing. If you are going to remove the caterpillars manually, make sure you stay covered, wear gloves and use a protective breathing mask.
Box tree caterpillars are protected from usual shop-bought garden insecticides by their shroud of webbing, requiring you to spray them directly, at which point you may as well pick them off instead.
Our method of exterminating box tree caterpillars is to apply a professional-use organic insecticide directly to the leaves, which poisons the box tree caterpillars when ingested.
As we need to throughly coat the entire tree, we may spend many hours treating a box tree caterpillar infestation. We will also visit at least two times so that we can exterminate any caterpillars that hatched after our initial treatment.
Our box tree caterpillar treatment also has the benefit of not affecting any beneficial wildlife, such as bees, and is completely non-toxic for birds, pets and people.