If you venture into the walled garden and have a look at the pond, you will be struck by two things. Firstly, the amount of floating algae, and then, that all of the iris and bulrush plants have been eaten by something. The algae has been caused by pond management which releases nutrients from the sediment into the water column, where it is readily taken up by floating algae. Although we undertook the work in autumn which limits nutrient uptake the following spring, the deep water and lack of submerged aquatic plants has meant that excess nutrients are plentiful. The management was needed to control the water soldier which had got just a tad abundant.
If you look carefully at what remains of the iris and bulrush, you will notice little caterpillar type animals.
These are not actually caterpillars, but the larvae of sawflies. You can tell they are sawfly larvae as they have more stumpy legs than caterpillars. Sawflies belong to the family of bees and wasps, but the ovipositor is saw like, although many are more like a drill. The eggs are deposited in plants, and usually, the species of sawfly are specific to a certain plant, which they are often named after, for instance, there is a gooseberry sawfly, and a turnip sawfly etc. What eats the leaves of iris ? Go on, have a guess.
What is interesting here is that the iris sawfly larvae are eating the leaves of bulrush, which used to be called reedmace, and before that, was called bulrush. But no-one wanted to call bulrush reedmace, so they changed it back to bulrush. Who are these people ?
Anyway, we in conservation call it Typha, which is the scientific name, cause I is a scientist. And Typha is very invasive and needs to be managed annually to prevent ponds losing open water. And as the scientist what I am, I’m quite excited by iris sawflies eating Typha. Maybe we can genetically modify them to create massive sawflies which will mean we never have to clear ponds again. But if we do that, we will never have the joy of watching volunteers submerge.