A new species of moth which has markings that make it look like a bird dropping, protecting it from predators, has been discovered in Devon.

The insect was declared to be new to science after its caterpillars were found by an amateur naturalist among oak leaves in the National Trust's Hembury Woods. The strange white caps covering its eyes make it look like a bird dropping.

Bob Heckford had stopped off briefly in the woods to see what moth species he could spot when he found a bright green, leaf-mining caterpillar he had not encountered before.

He contacted Dr Erik van Nieukerken, an international authority on moths, who, after raising some of the caterpillars until they turned into adult moths, declared them to be a species never before recorded. The tiny moth, which has a striking orange head, was officially described by Dr Van Nieukerken, of the National Museum of Natural History in the Netherlands, who named it Ectoedemia heckfordi in honour of the man who found it.

Mr Heckford, a solicitor, said he was quietly pleased at being able to claim a world first, especially as finding a new species is such a rarity in Britain.

He said: "I knew when I found it that it was new to Britain but it was Erik who told me it wasn't found anywhere else in the world.

"It's nice for something like that to happen. I'm very pleased. It's very nice to think there's something that hasn't been found before and it's in Devon – you usually have to go to the tropical rainforests to find something new."

The micro-moth has a wingspan of 6mm and its body is 3mm long; it has a creamy band around its middle and white hoods protecting the eyes. Leaf-mining caterpillars eat the leaves from the inside and leave empty tracks – mines – as they gouge their way along, without breaking through the skin of the leaf.

Since finding the first caterpillar, the species has been found at three other places in Devon, each time on oak trees.

Matthew Oates, a Nature Conservation Adviser and a moth expert at the National Trust, said: "This is new to science. That's very significant and shows you don't have to go to the Amazon to find new species." He said it was unclear what role the eye caps play but it is suspected they evolved to avoid the attention of birds. "It's possibly for camouflage," he said.

"Birds tend to aim for the eyes, even a species as small as this. The eye caps may be an attempt to make the moth look like a bird dropping. This tactic is used by quite a few insects."

Paying tribute to the long tradition of amateur naturalists in Britain, Mr Oates said: "We hear so much about the losses to the natural world, and less about the gains; which makes this find, however small, so important. Amateur naturalists have a wonderful window on the wildlife world and nature continues to amaze us."

The moth was discovered in the autumn of 2004 but was described only this year, in the scientific journal ZooKeys.

It's not the first time Mr Heckford has found micro moths that were previously unknown in Britain.