These 'Zorro' flies attack elm trees, and they're now in the UK!

Last updated at 08:10
Image showing the squiggly line the caterpillar has left on a leaf as he had eaten a section from the middlePA

This isn't the typical kind of hole you'd expect to see on a leaf. This one's pretty squiggly.

In fact it's almost like the 'Z' sign crime-fighting film character Zorro draws to show his enemies where he's been.

The distinctive pattern is actually the signature move of a particular type of fly from Japan called the zigzag elm sawfly.

But the patterns they leave might look pretty cool, the creatures are actually a pest - and they're thought to have arrived in the British countryside.

Royal Botanical Gardens Edinburgh have found the marking on elm tree leaves in Surrey, in the south-east of England in autumn 2017.

Zorro flyGetty
None of the flies have actually been spotted in the UK yet, so we've been imagining what they might look like - in a Zorro outfit

The flies only feed on elm trees, and researchers there are concerned about the effect they will have on the trees.

Zigzag elm sawflies rarely kill trees, but large populations can result in the tree losing all it's leaves because of the damage.

They're also worried about the impact it might have on other insects that depend on elm trees.

It's not just the UK that the elm sawflies have come to - they've already quickly spread throughout Europe.

They can also grow their numbers much faster than other insects because the females don't need a male to be able to reproduce.

So what can you do to help?

Many slippery elm tree leaves in sunlight with yellow green tintGetty Images

Well if you see a elm tree where these sneaky flies seem to have paid a visit you can report it.

Scientists want the public to help monitor the spread of zigzag elm sawfly, and report sightings using a website called TreeAlert, an online reporting tool developed by the Forestry Commission to track tree health problems.