How to identify, fight and prevent the box caterpillar in your garden

Box caterpillars are a common pest in the UK, and they can cause significant damage to your garden if left unchecked. Thankfully, there are several ways to identify, fight, and prevent box caterpillars from wreaking havoc on your plants. 

In this article, we’ll discuss what box caterpillars are, how to identify and get rid of them, and methods to prevent them from entering your garden in the first place.

What are box caterpillars?

Box caterpillars, also known as box hedge caterpillars and box tree caterpillars, are a type of moth that feeds on the leaves of box trees (buxus) and hedges. They’re native to East Asia but have been spotted in domestic gardens in the UK since 2011 — it’s believed that they arrived on imported Buxus plants. 

Box caterpillars can cause severe damage to box hedges and trees by stripping the leaves off in large numbers, leaving a skeletal, dying plant. 

Many insects provide a tasty, nutritious snack for the birds. However, box caterpillars are full of foul-tasting toxins from the Buxus plant, so birds tend not to eat them. So, without a natural predator, box caterpillars can be a real problem in a domestic garden. 

What does a box caterpillar look like?

Box caterpillars have black heads, green bodies, and distinctive black and yellow stripes. Like most caterpillars, they eventually transform into moths. 

Box moths are nocturnal insects with white wings spanning 4cm. Their wings are edged with a dark brown trim and a little white “horn” halfway across the outside of the wingspan.

What is the box caterpillar’s life cycle?

The box caterpillar has a fascinating life cycle, beginning at the egg stage. Female box moths lay hundreds of small, round, yellowish eggs on the underside of leaves, which hatch in just a few days. 

After hatching, the box caterpillar larvae feed on the leaves of their host trees for several weeks, growing larger 

until they’re ready to transition to the pupal stage. At this stage, they attach to a stem and spin a silken cocoon, remaining wrapped in silk for up to three weeks. 

During this period, the caterpillar undergoes a complete metamorphosis, emerging as an adult moth. The box caterpillar moth is active at night.

The box caterpillar moth is a pollinator and is most active during the summer months. During this time, female moths lay eggs on their host trees, starting the cycle anew. 

Identifying the signs of box caterpillar infestation

The first sign of a box caterpillar infestation is usually the presence of small, oval-shaped holes in the leaves of your box tree or hedge. These are caused by the caterpillars feeding on the leaves. 

This very hungry caterpillar eats the plant’s leaves, leaving faded or brown patches across the bush. However, the worst damage tends to start around the base of the bush, expanding upwards.

Box caterpillars are most active between March and October, during which time they can destroy a box plant within a week. 

Other signs of infestation include:

• the presence of caterpillar droppings on the ground beneath the tree or hedge and 
• white webbing on the leaves or branches as the caterpillar enters its pupae form before transitioning into moths.

Why box caterpillars and box moths thrive in the UK

The main problem with box caterpillars in the UK is that they have no natural predators here. So, the only option is to use biological or chemical solutions to control and eradicate a population invading your garden. 

How to get rid of box caterpillars naturally

Once you’ve identified a box caterpillar infestation, there are several methods to get rid of the pests. 

Pick box caterpillars off the plant

The first way to naturally remove box caterpillars is by manually removing them from the plant. You can do it by hand or by using a vacuum cleaner to suck the caterpillars off the plant. 

Make sure you wear gloves and wash your hands thoroughly after touching them — they may release poisonous chemicals onto your hands. 

Use a pheromone trap

Pheromone traps contain a synthetic box moth pheromone that attracts male moths, catching them to disrupt the breeding cycle.  

While these traps can be effective, you need to replace them regularly, and they won’t catch every single male. So, while they will interrupt breeding, these traps aren’t guaranteed to eradicate the problem completely. 

Microbial insecticides

You’ll need a professional to administer the Bacillus thuringiensis bacteria that will stop your box caterpillar infestation dead. And while it’s an effective biological approach, it can be costly.

Natural pesticides

Some natural pesticides are available that use essential oils repellent to the box caterpillar population.

 For example, the Box Plant Health “Cleanse & Shine” treatment deters caterpillars from eating the leaves of plants sprayed with the oil mix. 

And win-win: this particular treatment makes your box plants’ leaves shine for a healthy-looking box plant. 

Prevention: how to keep box caterpillars out of your garden

The best way to prevent box caterpillars from entering your garden is to ensure that the area around your plants is kept clean and tidy. This means removing dead leaves, twigs, and grass clippings from the site and keeping the garden free of weeds. 

Additionally, it is essential to regularly inspect your plants for signs of caterpillar infestation – as early detection can help to prevent a full-scale infestation.

Additionally, you can use natural repellents, such as garlic and chilli powder, sprinkled around the base of your box plants to deter these little critters.

Chemical treatments for box caterpillars

If natural treatments are not enough to eliminate box caterpillars, you’ll have to rely on harsher chemical treatments. 

However, it’s essential to be aware that chemical treatments can affect other beneficial species, such as bees — so, use these as a last resort.

Box caterpillar insecticides are available online but follow the instructions closely to avoid damaging neighbour plants and wildlife. 

How to deal with box blight

Box blight is a fungal disease that affects box trees and hedges and cause severe plant damage if left unchecked. 

If your buxus is affected by blight, you’ll notice the following symptoms:

• Brown leaves that drop off the branches
• Black streaks on young stems, possibly dying back
• White spore masses underneath infected leaves

The best way to deal with box blight is to:

• Prune the affected branches, cutting off slightly more than you consider necessary
• Apply a fungicide to the affected areas
• Avoid touching healthy box plants until you’ve thoroughly washed your hands

If the problem persists, remove the affected plants and replace them with new ones.

The best plants for deterring box caterpillars

Box caterpillars and moths don’t like lavender, garlic, rosemary, and chrysanthemums. 

These plants have strong smells that can help repel the caterpillars and provide an attractive addition to your garden. So, consider planting them around your box plants to help deter box caterpillars and moths. 

Conclusion

Box caterpillars can cause significant damage to your garden if left unchecked, but thankfully there are several ways to identify, fight, and prevent them from wreaking havoc on your plants. Following the steps outlined in this article can help keep your garden free from box caterpillars. 

Get in touch

Hopefully, you feel better informed about your grass type, but if you have more questions, we’d be very happy to help.

If you have any questions, email us at hello@moowy.co.uk. We’re looking forward to hearing from you.

Thanks for reading.

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Louis Hooft

Founder & Lawn expert

Introducing Louis Hooft, the founder of MOOWY and your reliable expert. With a profound love for stunning lawns and extensive experience in garden maintenance, Louis is here to assist garden enthusiasts in achieving a greener and livelier outdoors than ever before. Count on Louis for invaluable tips, clever tricks, and top-notch products to make your garden flourish!