Monday, June 22, 2009

Poisoners













There’s an interesting collection of poisonous plants growing in the sand dune system at Warkworth in Northumberland. Of these the most notorious must surely be hemlock Conium maculatum (bottom photograph), which produced the poison that the Greek philosopher Socrates used to commit suicide when he was condemned to death for impiety in 399 BC. The dull red blotches on the stems (second photograph) and a mousey smell are key identification features for this lethal plant, whose main toxic compound is the alkaloid coniine, which is also present in several other poisonous members of the carrot family. The middle photographs are of male (lower) and female (upper) plants of white bryony Bryonia dioica, a deadly poisonous member of the cucumber family that was once cultivated as a medicinal herb. In this species the female plants are particularly conspicuous in autumn, thanks to a crop of glossy scarlet berries that look good enough to eat – which would be a fatal mistake. The top photograph shows the poisonous caterpillar of the cinnabar moth Tyria jacobea, which accumulates toxins from the poisonous ragwort Senecio jacobea that it feeds on. Those warning colours ensure that any bird that attempts to eat it and suffers its unpleasant taste will remember the experience and won’t make the same mistake twice.............except that I have a hunch that cuckoos might be immune. We’ve often seen cuckoos feeding on the ground in the dunes at Warkworth when the cinnabar moth caterpillar season is at its height, and I have a strong suspicion that this is the caterpillar that they’re after. If that is the case, then as far as cuckoos are concerned that orange and black colour scheme must serve as a conspicuous advertisement, rather than a deterrent...

4 comments:

  1. Phil, I never knew the Cinnabar Moth caterpillar was poisonous. I've seen quite a few locally; I'll have to approach with caution in future. Striking colour though, and they always stand out.

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  2. I recall from a dusty corner of my memory that cuckoos do indeed eat cinnabar caterpillars and I've just double-checked my facts here in the 'Birds of the Western Palearctic'. Apparently, they also eat lots of the hairy caterpillars that other birds leave well alone. The gizzard is adapted for dealing with the hairs by sloughing off the mucous lining now and again which the bird regurgitates. They also produce pellets of caterpillar hairs, it says. Queer birds all round, cuckoos.

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  3. Hi Keith, one of the strange things about this moth is that it's common along the coast in Northumberland but you never see it here in Durham, even though there's no shortage of ragweed for it to feed on.

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  4. Thanks Nyctalus, you've confirmed my suspicions. Warkworth dunes are certainly a prime site for finding cuckoos, and this must be part of the reason, together with all those meadow pipits' nests to parasitise....

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