tadpoles without legs
 

Hi, My query is about the tadpoles in my pond .I have had the pond for 3 years. i introduced frog spawn for the first 2 years. this year frogs returned to the pond and produced their own.Which has hatched and produced tadpoles.But this year they seem to be taking longer to develope into frogs.We have had some that have left the pond,but still seem to have quite a few tadpoles left in there that have not developed legs.In previous years they have developed and left the pond a long time before now.We are nearly into November and they have stll not developed.Can anybody give me any reasons why this is happening. Neil