The mystery of the Roadford Lake 'tree frog spawn' solved

What leaves frog spawn six foot up a tree? There is a rational answer, and it doesn’t involve a new breed of super-frog!

Staff at Devon Wildlife Trust’s Working Wetlands project recently made a surprise discovery when working on land near Roadford Lake, in north Devon. They were quickly able to identify the jelly-like substance as frog spawn but weren’t able to fathom how it had come to be on a tree trunk.

Project Manager Mark Elliott picks up the story: "Finding frogspawn at this time in winter is not that unusual, especially the mild weather of the past week. But finding it up in a tree was. It’s not something I’d come across before. Common frogs lay their spawn in water and it’s there that tadpoles develop. Not in trees!"

Mark took a photo of the frog spawn and sent it to Devon Biodiversity Records Centre for identification. It is DBRC’s job to keep a central archive of the county’s wildlife records. Staff there process thousands of biological sightings each year. The experience and expertise gained from this work meant that staff member Ellie Knot had seen similar cases before and was able to add an explanation to the puzzle.

Ellie said: "This kind of finding is commonly known as a 'star slime' - a lot of animals and birds eat frogs, but they don't eat their ovaries because the eggs or spawn contained in them expand massively when they come in to contact with water. This expansion would be enough to give anyone stomach-ache! Freshly laid spawn is fairly small - the eggs (in their jelly cases) are less than 5mm across, but once it has been around for a few hours the eggs expand to more than 1cm across.  The clump of frog spawn usually ends up much larger than the frog that laid it. So, when birds etc eat a frog they leave the ovaries behind, which then expand and burst when they get wet, leaving a clump of spawn."

"In fact, it is not that uncommon to find frog spawn in trees - buzzards and crows will often take frogs, retreat to a nearby perch and then eat their prey there, leaving the ovaries and the spawn behind after their meal."

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