This is a nice plant: Tansy, Tanacetum vulgare. It used to be considered "necessary for a garden" but now is relatively uncommon. I've noticed that since the re-development of Lewes Road going into Brighton the central verge is packed with this bold perennial.
It is a member of the Daisy family and is of the kind which lacks the peripheral ray florets found in Bellis perennis and makes up all of the florets in Dandelions.
It contains a potent chemical which can cause liver damage in large amounts. However it is an effective insecticide/insect repellent, having been used through the ages in the treatment of intestinal worms.
There was a vogue for burying the dead with tansy to prevent insects attacking the corpse. The first president of Harvard was buried in a coffin stuffed with tansy which was sufficiently well-preserved to allow him to be identified when the remains were moved during re-development of the graveyard.
There is a (threatened) beetle, the Tansy beetle (Chrysolina graminis), which depends almost exclusively on the plant. It looks like a very large Cryptocephalus aureolus (see May 25th).
Today the moth book arrived. Tonight David's moth trap is set in the orchard. Tomorrow we will have moths!