Ragwort and nature’s circle of life

Outdoor Living

KNOCK ON EFFECT The eradication of ragwort can be linked to the a decrease in the population of the cinnabar moth and the Cuckoo.  Pic: istock

Country Sights and Sounds
Michael Kingdon

An Buachalán buí is back in town, and I for one am glad to see him.
His proper scientific name is Senecio jacobaea, which I can only translate as ‘The old man James’. ‘Senecio’ is derived from ‘Senex’, the Latin for ‘old man’, which probably gives reference to the grey and wooly appearance of the seed heads as they ripen. ‘Jacobaea’ means, ‘of James’.
But we know him best as the Yellow boy, an Buachalán bhui, or even more simply as ragwort. And yes, we’re happy to have our ragwort back.
While this is one of our most poisonous wild plants it is nonetheless an important one for wildlife, and especially for a little known and, sadly, rarely seen nocturnal insect, the cinnabar moth.
The cinnabar is among our most beautiful moth species, although as it mainly flies at night we rarely get to meet it. But when we do we cannot help but be impressed by the striking blood-red and jet-black markings of this inch-long lepidopteran.
Ragwort was an important inclusion of the Noxious Weeds Act of 1936, under which owners or occupiers of lands are still obliged to prevent the growth and spread of unwanted wildflowers, including ragwort, thistle and dock.
We can understand this, for all parts of this plant contain alkaloids which cause potentially fatal liver poisoning in grazing and browsing animals, perhaps partly by promoting the accumulation of copper. While cattle and horses ordinarily avoid the bitter taste of ragwort, if food is short they will begin to eat it. When it is dried and saved in hay it loses its bitterness but retains its toxicity. Some say sheep are largely unaffected and I even heard of sheep being used to nibble ragwort out of pasture.
A few years ago many took the Noxious Weeds Act to heart and set out to eradicate ragwort altogether, and indeed it did disappear from large tracts of land. And when it did, so did the cinnabar moth. In areas where ragwort survived it remained in a position to make a resurgence. Each mature plant might produce as many as 200,000 viable seeds from late summer into autumn, each of which can be carried huge distances by the wind, and which can wait in the soil for decades before germinating.
Our cinnabar moth, by comparison, can only move a short distance from the place it has started life. Each breeding female will lay from 200 to 300 eggs, all of them on ragwort – provided she can find a male to mate with one of these moth-deficient nights.
Many will be familiar with the yellow and black-striped cinnabar caterpillars. We see them almost exclusively on ragwort, although where growth of this preferred food plant is suppressed they will attempt to feed on groundsel. However, as groundsel is much smaller and lighter the hungry caterpillars soon consume everything and must find another food source.
Then they turn on each other, with the strongest individuals devouring their weaker siblings, each of which has been accumulating ragwort poisons in its own body. Other animals somehow recognise the yellow and black markings as a warning sign and avoid eating these caterpillars.
There is one bird that pays no heed, and that is the cuckoo. Cuckoos consume a great number of caterpillars, regardless of colour or toxicity.
But wait now; did anybody else notice the scarcity of cuckoos this year? Yes, we heard them calling alright. But not so long ago May and June would have the woods and fields resonating with those enigmatic calls and there would hardly be a moment we wouldn’t hear more than one.
So over the years we managed to get our ragwort under control. When we did so, we inadvertently also lost most of our cinnabar moths. Where ragwort and moth survived together they became the focal point for hungry cuckoos, which quickly eradicated local populations. Deprived of an important food source, cuckoo numbers have fallen dramatically. Of course there are other factors involved in the near disappearance of numerous bird species, but it isn’t difficult to make one connection here.
With no caterpillar infestation, an Buachalán bui has found his feet once more.
Perhaps, we hope, the whole thing will go full circle and we shall have our enigmatic cuckoo back in its full complement, and also have those cinnabar wings spiraling like miniature fireworks in and out of torch beams as they were fifty years ago. And in the meantime we might have learned a lesson.

Michael Kingdon formerly wrote these columns under the pseudonym John Shelley. A naturalist and keen fisherman, he lives close to the shores of Lough Carra.