Monday, 27 August 2012

In Praise of Ragwort

Ragwort doesn't have a great reputation, it is one of just five species of plants listed as an "injurious weed" in the UK, chiefly due to its toxicity to horses and cattle. The toxicity comes from a cocktail of chemicals called alkaloids, which if consumed in large quantities can cause severe liver damage to mammals. The alkaloids are toxic to most insects as well, but there are some thirty species which can not only tolerate consuming ragwort, but are entirely reliant upon it.

Undoubtedly the most common and widespread of these species is the cinnabar moth, whose caterpillars can  reliably be found on almost any decent stand of ragwort. Turning the plant's defences to their own purposes, the caterpillars incorporate the toxins into their own bodies, and then advertise their distastefulness with bold orange and black stripes. 

Cinnabar caterpillars
Cinnabar caterpillars munching their way through ragwort

Cinnabar Caterpillar
Close-up of a single cinnabar caterpillar

The adults are equally toxic, and even bolder in their advertisement, going for the classic warning colours of red and black. The sight of an adult moth bursting out of the undergrowth in a blaze of colour often leads to people searching through their butterfly books for a bright red or pink species.
Cinnabar - 2069
Adult Cinnabar moth

In addition to the specialist species, some of which are extremely rare, there are a host of species for which ragwort provides an invaluable source of pollen and nectar, especially in the wasteground areas which it frequently occupies. At this time of year ragwort is the first plant I head to when looking for interesting insects.

One of my favourites is the mining bee Colletes fodiens, another species lacking an English name, perhaps it could be the ragwort bee? Although not entirely reliant on ragwort, I seldom see it on any other flower. Superficially resembling a small bright honeybee, the broad white stripes on the abdomen instantly distinguish it as a Colletes species, although separation from the other Colletes species is somewhat trickier, see here for some further information.

Colletes fodiens
Colletes fodiens foraging on Ragwort

On any given day there are over a hundred other species which could be found on ragwort, below is just a small selection of the variety of life supported by this one "injurious weed". There is no doubt that ragwort can cause problems when in the wrong place, but in the vast majority of cases it is a extremely valuable component of the British countryside, and one which deserves a better reputation than it currently possesses.

Meadow Brown
A common sight of the British summer, a Meadow Brown

The Forester - 163The striking Forester Moth, now a somewhat scarce and declining species

Antler Moth - 2176
The attractively patterned Antler Moth

Syrphus ribesii
A classic hoverfly, Syrphus ribesii

Red-tailed Bumblebee
A red-tailed bumblebee, one of several bumblebee species to be found on ragwort

Stictopleurus punctatonervosus
Stictopleurus punctatonervosus, a recent colonist to much of the UK

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