The butterfly has bright orange, brown and yellow markings
Volunteers have been recruited to help spot a rare butterfly which is very choosy about its diet and habitat.
The marsh fritillary is critically rare and can only be found in wetlands in the north and west of the UK. In Wales this means only parts of the Llŷn Peninsula and Anglesey.
"They're the equivalent of the panda in that they're doing their best to get extinct," said Dave Thorpe of the Environment Agency Wales.
Emerging as a butterfly each June, the marsh fritillary is in the caterpillar stage during the autumn.
In October a group of volunteers joined Dave on an outdoor lesson in how to spot and count the tiny creatures.
"Firstly, we check for their food - devil's bit scabious," said Dave, who led a day out at the Cors-y-Wlad reserve near Clynnog Fawr in Gwynedd.
"It's a pretty blue flower. At this time of year, the caterpillars live in colonies, and sit in a web on the plant, much like a spider's web."
The marsh fritillary is in particular danger because it can only feed on this plant, and doesn't fly more than 100 metres in search of more habitation on which to lay its eggs when in butterfly form.
"They need wet grassland grazed by cattle or ponies, but not sheep," Dave explained.
The marsh fritillary's numbers fluctuate greatly according to the weather
"The females lay their eggs as soon as they emerge on the nearest devil's bit scabious plant.
"But they're rather lazy, and very reluctant to fly unless it's hot, sunny weather, so they're not easily able to colonise new sites."
Volunteer training days have been arranged by Gwynedd Council over the past two years.
Dave Thorpe suggests anyone who does spot the caterpillar of the marsh fritillary should contact
, the body which records plant and animal life in north Wales.
He recommends sending photos of animals or plants you can't identify to
, where experts are on hand to help identify them.