The Lincolnshire Bird Club

On the 15th of April I watched a female Brimstone in my tree nursery. From a choice of 10000s of plants of at least 50 species it picked out a handful of Alder Buckthorns, Rhamnus frangula, and laid eggs on the tiny leaves which were only just starting to emerge from the buds. We also have Purging Buckthorn, Rhamnus catharticus, on the nursery but as far as I could see this was ignored. I presume that the butterfly was guided by smell to its food plant, a quite remarkable feat. The Alder Buckthorns complete with eggs have been potted up, does anyone have any suggestions for following the next stages in their life cycle?
Hugh Dorrington

Having potted up the Alder Buckthorn back in April I could find no sign of eggs or caterpillars at the beginning of May and assumed that I had lost them. On or around the 20th of May I had another look and could see some eaten leaves, closer inspection revealed 4 or 5 small pale green caterpillars which I presumed to be the Brimstones. Last week-end I watched a Willow Warbler working its way through some young birch trees just a couple of metres from the Alder Buckthorns. If the caterpillars are eaten, it would be nice to think that they are being fed to a brood of Willow Warbler chicks.

Hugh Dorrington

Good news! There are at least 7 Brimstone caterpillars on the Alder Buckthorn, about an inch long. The biggest appear to have some gossamer threads around them as if starting to prepare a cocoon.
It looks as if the Willow Warbler was feeding on aphids which are all over the birch trees. I hope it returns with its young.

Hugh Dorrington