Nature 2015 August

Nature Notes – August 2015

Sometimes Science Truth is Stranger than Science Fiction

I can remember in the nineteen-sixties being introduced to my first Giant hogweed towering above me on a bomb-site in north London and being warned by my father that we should avoid being stung by its vicious spines whilst trying to net the butterflies that were on it. Unknown to me at the time but by chance this first encounter probably coincided with the release of the film adaptation of John Wyndam’s novel The Day of the Triffids Skip ahead to the early 1980s there was a television adaption of the book. Within a week or two nationwide alerts, warning the populace to be wary of mixing it with the hogweed. As in the TV programme ‘the authorities’ were exhorted to exterminate this evil invader. Much as was the case in the book the best that came be said is that the plant was temporarily kept at bay. Move forward 30 years and I saw similar news reports to those in the ’80s that this monster is on the march again. As far as I am aware there is no film remake just about to be released.

Familiar relatives of the hogweed include Cow parsley and the humble Carrot but that’s the extent to which any comparisons remain valid. In one respect there are stronger similarities between triffids and hogweed. Both invaded these shores. In the case of hogweed it was first introduced as an ornamental garden plant by plant hunters who brought it back in 1893 to the UK from the Caucasus, today the boarders of Lithuania and Russia. The wealthy Victorians had developed a passion for creating sunken gardens with water features and the hogweed thrived on marshy ground. Taking two years to reach maturity it could reach over 4 metres. By investing in substantial growth it could produce massive seeds, up to 50,000 per plant, that would survive dispersed downstream and beyond the boundaries of the estate. Despite the frequent adverse publicity, many remain unaware that the spines on stems and leaves inject a phytotoxin that reacts when the skin is exposed to sunlight to create painful rashes and blistering which can result in long-term skin damage. Sensitivity varies greatly between people and there is recent scientific evidence that certain strains of DNA contain genes which happen to imbue almost total resistance. What remains a mystery to science is not so much why such resistance may occur in humans but rather what herbivores required the Hogweed to evolve such a pernicious toxin in its home territory the Caucasus and why it has continued to manufacture this poison long after the graziers that it needed to deter had become extinct.

No natural history documentary on the African savanna is complete without at least some of the signature beasts: Buffalo, Elephants, Giraffes, Rhinos, and several of representatives of herding grazers such as, Zebra, Gnus etc. Whilst not given starring roles guaranteed to be present as the camera pans across the scene is a bird with a rather specialised if somewhat distasteful diet. Oxpeckers are the birds with razor-sharp yellow or red beaks seen poking around on the heads and backs of these large animals. Their principal food are the arthropods which parasitize such mammals like the arachnid ticks and the larvae of insects which lay their eggs in wounds on hides. Aside from providing the service of easing the animals of their unwanted hangers-on the oxpeckers also provide an early warning by hissing when there is impeding danger in the form of predators, big cats and hunting dogs etc.

Until a short while ago I thought we had no equivalent example in this neck of the woods. True the story is told of how the once woodland bird the Robin accepted a lift on the back of wild boar, and possibly pigs let loose in woods in the autumn, to benefit from the worms and other invertebrates unearthed by the snout of the porcine. Once humans began to turn over the soil the robin is said to have adopted the habit of following and landing a few paces behind to grab any worms etc; thus disturbed. The robin expanded its realm when it began to perch on the gardener’s spade as they weeded their garden patch which provides a modern retelling of the tale.

Last month on a sunny afternoon I was struck by the ever-increasing number of the large number of Magpies squabbling as they congregated in the trees or on roofs around our garden, periodically descending onto the grass to scavenge for morsels of this or that. Daphne du Maurier’s science fiction horror story The Birds (far more frightening than Hitchcock’s film adaptation) comes to mind. Then in their midst came a pair of female Muntjacs, browsing as they went. They suddenly stopped grazing the grass and stood side-by-side in the middle of the lawn. Next a magpie already on the ground hopped towards them and suddenly flapped wings gently and alighted on the back of one of the deer. I thought this was a typical gesture of aggression aimed at the intruders. But no instead of bolting into the shrubbery the pair stood still seemingly unmoved by the experience. What’s more the magpie began to inspect the coat of the first muntjac and seemed once or twice to find something of value to consume. A few moments later the magpie hopped across to the back of the second deer and repeated its inspection before alighting back on the grass. The brief encounter over the muntjac strolled on and began feeding. OK so one incidence is not enough to form any firm conclusions that the magpies were removing ectoparacites in the same way as oxpeckers. While I am yet to find a specific reference to this behaviour with muntjacs there are accounts of similar behaviour occurring with fallow deer.

During the last twelve to eighteen months I have been delighted to see a return of Tree sparrows to our garden. It’s pleasing to applaud the return of this cocky little chappie. Though just an occasional daily visitor at first but the frequency of visits has steadily increased and these last months the numbers have mushroomed as fledglings in quite large numbers have appeared. Unlike their urban cousins, the House sparrow, localised Tree sparrow populations fluctuate greatly, each cycle perhaps lasting anything between five and ten years. Being birds that can congregate in large numbers they can be susceptible to food shortages year to year and these local populations may mysteriously disappear from one locality only to mysteriously reappear years hence. (The Sparrow is a 1990s science fiction novel about a mysterious return from outer space). Being predominantly seed eaters amongst the varieties of wildflower produce available they will no doubt be grateful consumers of the fruit of the Giant hogweed!

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