Friday, 24 August 2012

Dicing with Dangerous Natural History

Recent postings on Facebook from a naturalist who decided to acquire personal experience of the effects of giant hogweed on her arm reminded me of someone I knew in the New Forest who wanted to find out about the effects of the bite of the large tabanid fly Tabanus sudeticus. There cannot be many who have not been plagued by that silent but deadly pest, the horse-fly but how many have actually been bitten by other tabanid flies in Britain. Of course in Africa, it is a tabanid fly, the tsetse fly that carries the deadly sleeping sickness.

Giant Horsefly, Tabanus sudeticus, New Forest
The Giant Horsefly Tabanus sudeticus is comparatively common in the New Forest where it preys on horses. New Forest ponies can often be seen rushing around to avoid being bitten by the noisy Tabanus sudeticus which is certainly not as insidious and silent as the horse-fly we all know and hate. However once on a horse’s back, and in a part of its anatomy where the tail cannot brush, Tabanus sudeticus can cling on and will not be disturbed as it feeds. The chances of any human being bitten by Tabanus sudeticus, as it is such a clumsy, noisy beast are remote. A naturalist friend of mine decided he wanted to experience personally the effects of this fly. He caught one in a jam jar, and then applied it to his hand. The fly took some time to take the hint, but eventually began by scything with its mouth parts to make a wound. Blood began to escape from the wound, and the fly enjoyed its meal. My friend’s first reaction was “Well that’s pretty innocuous.” However, a few hours later his hand swelled up like a balloon, and he became really very ill.

Poison Ivy, Dallas, Texas
I remember the first time I visited Texas being tempted to see if I were effected by poison ivy. In retrospect, I think to have conducted an experiment on myself would have been both foolish and unpleasant. I remember my wife telling me about an Indian colleague of hers at work who complained that in Britain, brushing against vegetation was strangely unpleasant and hurtful. The fact was she had never experienced stinging nettles before. A few years ago, I was undertaking an ecological survey in East Sussex when I found a nettle with narrow leaves. I had recently heard about the Fen Stinging Nettle Urtica galeopsifolia that has narrow leaves, and is supposed not to sting. Having looked at the leaves carefully and being fairly reassured that there were few, if any stinging hairs, I touched it gingerly. I was not stung. Was this a good enough indication that I had found the species? In fact, I still believe that the actual status of Urtica galeopsifolia is in doubt, and that it may simply be a form of the normal, unpleasantly painful stinging nettle we all know and avoid.

As a naturalist, reactions to danger can be less healthy than those of other humans. I well remember being in the Pamir Mountains in Uzbekistan when a member of the party I was leading shouted up to me that he had spotted an Asian Cobra. My immediate reaction was to rush down the hillside, and I was rewarded by seeing the snake as it slid off into the undergrowth. On another occasion, my party was stranded in Tashkent. Our transport onwards to Kirghizia was delayed as senior soviet officials had purloined all the seats on the flight we were to have taken. We had a day that was fallow, and the local organisers of our trip wondered how to keep us amused. We were taken to a zoological institute, and shown cabinets full of bird skins. This did not keep us occupied for long. Then someone had a brainwave. Would we like to see the snakes? We were taken to the relevant part of the building and ushered into a rather small office. In the corner was a cage. Between us and its contents there was nothing but a layer of chicken wire. I was at the front of our group, and to say I was uncomfortable when the cage was opened would be an under-statement. The inhabitants of the cage reared up, fanning their heads as our host pushed his hand towards them. They were Asian Cobras. “They’re quite harmless,” our host explained, “Rearing up like that is all show. You really have to positively persuade a cobra to bite you.”

For the next stage of the visit, we were ushered into laboratory where a taciturn scientist was handling a Soviet species of pit viper. The most poisonous snake in the Soviet Union, he told us. He held it behind its head, and pushed its fangs into a beaker. Two jets of a colourless liquid squirted into the beaker, and these would be used to produce anti venom.

“Do you ever make any mistakes?” a member of the party asked. For answer, the scientist held up his hand. One of his fingers was missing, and he explained that he had to decide whether to use an axe lying close to him, or die.

Silk-moth caterpillar, with poison spines, from Ecuador
I am lucky in that I am not affected by the hairs on the tails of brown-tail moths. I have never actually done an experiment to prove this, but have come into contact with sufficient of them, and of other British caterpillars to know that I am probably immune. In Ecuador once, I came across the caterpillar of a species of silk-moth armed with vicious looking spines. Our local guide told us that those spines contained a venom quite powerful enough to put you in hospital.

There is a certain thrill that many humans, and probably many naturalists have in close encounters with dangerous plants and animals after they have got away with the encounter. On one occasion, a local guide told me of an eyelash viper behind a vine on a massive rain forest tree in western Costa Rica. I went down to investigate and failed to spot it.

“Your eyelash viper has gone,” I told the local guide when I saw him later.

“When was that?” He asked

“Oooh, about an hour and a half ago,”  I replied.

“Well it was there twenty minutes ago.” He assured me. After he told me exactly where it was, I went back and sure enough, looking obvious it was very much still there. I shuddered when I remembered that I had looked for lichens with a handlens on that tree when I thought it was safe to do so.

Eyelash Viper, Costa Rica
On another occasion in Costa Rica, the rest of my party went off horse riding for the day. I decided to have a day to myself. I walked off down several lanes, and found a dry hillside which looked promising. I became aware of a bird call which consisted of two whistle like notes. After a while, I found I could do the top notes, and the bird would reply with the lower note. Very gingerly, I began to approach the sound and I was rewarded with good views of a delightful Lesser Ground Cuckoo. When I got back to the centre, I told the local guide where I had been. After satisfying himself with my location he said. “That was not very sensible. That particular hillside is home to a large number of tropical rattle snakes.”

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