Caddis fly larva has never before been found on the island
The larva of a rare aquatic insect has been discovered on the Isle of Wight.
A caddis fly larva of the Molannidae family has been found in Horringford on the Eastern Yar, according to the Environment Agency.
The insect - uncommon in rivers in Hampshire and Sussex where the water quality is good - is sensitive to pollution, the agency said.
It builds a "sleeping bag" from sand gravel which protects and boosts oxygen flow. The larva was found last year.
The discovery was made as part of a routine procedure, known as kick sampling, which takes place in the same location on a river over a number of years to build up a picture of ecological diversity, a spokeswoman said.
Freshwater ecologist Emma McSwan said: "Isle of Wight rivers do not tend to contain the same diversity and abundance of invertebrate life as those on the mainland.
"What our find shows is that even a creature that is highly sensitive to water quality can survive in the Eastern Yar.
"That is good news. These species tend to be found in large sandy rivers with good plant growth."
Molannidae have been found in only one percent of samples taken by the Environment Agency ecologists in rivers across the Solent and South Downs area since 1989, according to the agency.
Sometimes only their cases are found, but these cannot be included in the final count because a live specimen is needed, it said.
Neither case nor live larva has ever before been found on the island.
Caddis flies are one of the largest groups of aquatic insects closely related to moths and butterflies.