Comfrey (Symphytum officinale) is well-known for its medicinal uses as well as its compost-making qualities and ability to improve the health of nearby plants. It contains calcium, potassium, nitrogen and allantoin – a natural chemical compound which soothes and protects the skin and promotes cell replication and the healing of wounds, burns and scars. No wonder it was known as Knitbone or Boneset by our forebears who made it into a poultice to soothe and reduce swelling around broken bones, thus helping them to mend.
I was recently surprised to discover that comfrey also plays an important role in the life of the African Monarch butterfly.
We have always grown patches of comfrey in different parts of the garden. The large dark green hairy leaves with delicate mauve or light-blue bell-shaped flowers provide an attractive and trouble-free addition to herbaceous borders, the bees love the flowers and if it spreads too enthusiastically, the leaves can always be added to the compost or chopped up and turned into liquid manure.
We recently decided to reduce one such patch and a few days later discovered at least 10 African Monarch butterflies fluttering about in a frenzy of delight – settling and seemingly feeding on any damaged or wilted leaves they could find. They have returned each day this past week, so I became increasingly curious about what they could be up to. After an extensive internet search, as well as investigating Steve Woodall’s informative books on butterflies and their habits, I discovered what they were probably doing.
Monarchs are large showy butterflies with a slow flight and conspicuous markings – in the case of the African Monarch (Danaus chrysippus) – tawny orange wings with black and white tips. These colours, along with the slow unconcerned flight, signify danger to potential predators. The African Monarch is bad-tasting and toxic. How does this happen? Monarch larvae feed on plants from the milkweed family (Aesclepias spp. e.g. Balloon Cottonbush), which often contain poisonous compounds. However these plant poisons are not carried across from larva to adult, as was previously believed. Plants like heliotrope, comfrey and some Senecio species exude bitter, poisonous alkaloids when damaged. Apparently male Monarch butterflies suck up the alkaloids and digest them to produce useful chemicals such as sexual attractants and bitter compounds that induce vomiting in any vertebrate foolish enough to eat them. During mating a male can transfer some chemicals across to the female so she can use them to create her own protective chemicals. So successful is this protective process that some non-toxic butterflies have mimicked the colours and markings of the African Monarch, for example the female Mocker Swallowtail and the female Common Diadem. Our African Monarch butterflies were clearly delighted to find a patch of damaged comfrey which could supply their protective toxins, and promote late summer/early autumn breeding.