When Megan Gimber plunges her arm elbow-deep into a hole in a tree, she never knows quite what to expect.
If she is lucky, it will not be the huge clutch of spiders that once swarmed out from inside an old apple tree.
A shock, for sure, but to do her job, she needs the grit to tough out a close encounter with our eight-legged friends.
The thing that Megan, key habitats officer for the People’s Trust for Endangered Species (PTES), really hopes to find in the powdery rotted wood is what ecologists call “frass” ... insect larvae droppings to the rest of us.
It can be a sign the tree is host to rare species whose very survival is hanging by a thread.
These are not the high-profile endangered creatures that feature in worldwide campaigns. Nor are they cute like dormice.
They are likely to be small, unglamorous beetles – the Cinderellas of the conservation world, but still a vital link in the chain.
Crucial to their survival is Britain’s unique woodland pasture, where ancient trees provide natural nooks and crannies in which they can thrive.
Even the more common insects, whose larvae feed on dead or decaying wood, are a prime source of food for species like birds and bats.
And Suffolk is now at the forefront of a campaign by the PTES to protect this precious habitat.
The charity is calling on nature-lovers to help with a pilot survey to assess the condition of more than 1,000 examples spread across the county. They include numerous sites around the Sudbury area.
Wood pastures – where large ancient trees grow in open pastureland – are under threat due to factors like urban development and conversion to arable farming.
They started life hundreds of years ago as wooded commons, medieval hunting forests, or deer parks.
But what makes it such a special habitat is deadwood.
“They call it dead, but it can be more alive than living wood,” says Megan, “because so many things live in it.”
The holes that develop in veteran trees, and the decaying heartwood inside them, provide food and refuge for a vast number species.
And appearances can be deceptive. A tree that looks on its last legs could have 200 years of life left.
Each venerable, craggy-barked veteran is a mini-community, home to all manner of life from lichens to woodpeckers.
But wood pasture-lovers like the lesser spotted woodpecker, and pearl bordered fritillary butterfly, are now on the endangered species red list.
And, as a group, saproxylic insects – those whose larvae feed on rotting wood – are among the most at risk in the whole of Europe.
Suffolk Wildlife Trust’s Old Broom reserve near Bury St Edmunds is a stunningly beautiful example of wood pasture.
Majestic oak trees up to 700 years old, including one so massive it is nicknamed Big Ben, are surrounded in places by carpets of bluebells.
The site is not normally open to the public, but volunteers for the PTES survey will be invited to a training day there on June 11.
“My biggest ambition is to let people know how important the deadwood habitat is,” said Megan, who studied biological science at Oxford.
“Many of the trees at Old Broom are classic old pollards, where the branches were chopped off every few years to make charcoal or animal fodder.
“It leaves wonderful knobbles where the limbs were cut and when holes and snags develop they become brilliant habitats.
“Fungi go in and find the dead wood and soften it, then the beetles come in.
“They reckon the trees here date from medieval times and were last pollarded 300 years ago.”
What makes wood pasture different from ordinary woodland is that the trees can grow to their full spread rather than tall and spindly.
“Most people know that trees are great for wildlife, but they grow better in the open than close together,” said Megan.
“It gives more long, low branches open to light where lichens can grow.”
Suffolk was selected for the pilot survey because wood pasture sites in the county had already been pinpointed.
“Someone from Suffolk Biological Records Centre had already created a map of different habitats,” said Megan.
“The survey is much more about the structure of the sites than the species.
“We’ll be looking at things like tree canopy cover, and other species like bramble, hawthorn, and elder which are good for insects.”
Some insects spend most of their lives as larvae, munching through the deadwood, before emerging as adults.
“Stag beetles are larvae for six years, then an adult beetle for just six weeks,” Megan explains.
Her Devon childhood prepared her for a career in conservation. “There was one bus a week from our village,” she recalls. “I grew up climbing trees, making dens and watching birds because all my friends were so far away.
“I was surrounded by biodiversity. I didn’t want to be part of the generation that lets it all get lost.”
Volunteers for the Suffolk survey, designed to be incorporated into a walk, will be sent a pack with detailed instructions, and a letter requesting the landowner’s permission.
The training day on June 11 is not essential but aimed at those particularly interested in the conservation of the habitat.
To find out more go to www.ptes.org/campaigns/wood-pasture-parkland.