The Natural Garden

Science with a bang

Burnet moths

      My first job, at the age of sixteen, was working as a laboratory technician at a South Manchester independent boys grammar school. The work entailed setting out experiments for what was then O and A level chemistry, physics and biology, keeping chemicals topped up and being a general odds body for the science teachers. There were three of us and one was a character named Ted. He was one of those blokes who was always one step ahead in terms of achievement or ownership: you'd climbed Kinder and he'd just got back from Ben Nevis (where he'd given the mountain rescue people a few tips); you'd got a new bike and it happens he'd got the more expensive, newer, model - most of us have come across the type, though we've never seen the proof of the ascent of Ben Nevis or witnessed the bike ( he always comes to work on the old one to save the other for best).

      Eventually this characteristic manifested itself in the workplace: one of the 'A' level students  had made some nitrogen triiodide by mixing iodine crystals with ammonia, then filtering and drying the solids. The resulting compound has great attraction to most boys because it's highly unstable and the touch of a feather is enough to cause it to explode. Sprinkled on the floor it has the delightful habit of going off when someone walks on it, often causing an impromptu dance a bit like that often seen in old cowboy films when the bully fires a six-gun at his victim's feet. Obviously, this appealed to us and we occasionally made a bit of the stuff and had a few laughs with it. However, unbeknown to the rest of us, Ted, as usual, was thinking bigger : we were sitting having our tea break one day during school holidays when there was an almighty explosion from upstairs at the far end of the building - the biology lab.

      "Christ!" Yelled Bunny "it's started!". Bunny, named in honour of his ears (we reckoned he'd move like the clappers if the wind was coming from behind), was worried more than most about the Russians and the Cold War situation we were in the middle of. This, to him, was undoubtedly the first attack.

      There was a short stunned silence, then we pulled Bunny from under the table and ran along the corridor and up the stairs to the biology lab.

       At first there was no visible damage but a sort of rustling noise coming from the far end.

      "Ah", said Ted, sheepishly, "I think the problem may be due to my triiodide. I put a bit of it over there", he pointed, "I thought it'd dry out quicker with the bulb under it".

      At the time, dissection of anything that moved was part of the biology curriculum and, for this purpose, locusts, rats and cockroaches were all bred in controlled conditions. Ted had put his nitrogen triiodide on top of the cockroach container which was  heated by a bulb attached to the glass lid. The container was really a large fish tank with bits of varied detritus and food in the bottom to keep the cockroaches happy. We walked over to it and at first I thought the crackling sound our feet were making was Ted's nitrogen triiodide. It wasn't. The noise was made by us standing on live cockroaches - thousands of them. The tank was now an ex cockroach container and pieces of glass were all over the lab. The adjacent locust cage (a large wooden box with a glass front and a small heater) was still mostly intact but a triangle of glass had been blown out. Locusts were pouring out of the hole and heading straight for the windows. Luckily, these were all shut because of the holiday, and the plague we foresaw never hit Manchester.

      "How much of the stuff did you make", I bawled at Ted, while we scrabbled to block the hole in the locust cage (this was eventually achieved in a highly professional way by stuffing it with toilet paper). He made a vague hill-like  indication with his hand, implying that (as expected) the amount we normally made was like an ant hill towards his Everest.

      They were American cockroaches, big, reddish in colour and very fast moving. I'm not sure what the difference is between them and other species but suspect that examination with a magnifying glass will show them to be wearing cowboy hats.

      I'd read somewhere that, should mankind be wiped out in a nuclear holocaust, insects will take over the world. In justification of this theory, it was interesting to see that these cockroaches had survived an explosion of devastating proportions. Reproduced on human scale it would have annihilated South Manchester. Admittedly,some of them were a bit wobbly on their feet, others were running in circles and, if you looked very closely, their eyes were revolving. However, on the whole, they were in pretty good nick and just wondering what the hell that bang had been.

      And so we spent a pleasant afternoon chasing cockroaches through a cloud of locusts intent on repeating their success in Egypt. Eventually, when we'd caught as many of the escapees as could be reasonably expected, we collapsed onto lab stools.

      "Well, that was a laugh, bet the buggers have all gone deaf", joked Ted, before going on to elaborate how his explosion was bigger than any that Bunny and I had managed.

      I expect that isn't the only occasion he's been beaten up.

Birds-foot trefoil (Lotus corniculatus) So called because seed heads look like birds' feet

      While we're on about plagues, we're all familiar with regular explosions of the greenfly population: Stephan Buczacki, in his book 'Pests, Diseases and Disorders of Garden Plants' offers the cheery thought that '.....a single black bean aphid alighting on a broad bean plant in early June could theoretically give rise to a population of 2,000,000,000,000,000 by the end of August'. This doesn't happen simply because of predation on them by bluetits, ladybirds, lacewings, hoverflies and other agencies. It's common sense therefore to present a garden which is wildlife friendly and to use pest controls which target only the pest. In the case of greenfly, a regular spray with a solution of washing-up liquid will deal with any that the natural predators miss.

Six spot burnet moths emerging from chrysalises

      However, not all insects and caterpillars are a problem to the gardener and by encouraging many of them we are adding another dimension of interest to our plot. This can be achieved by growing some of the plants known to host the desirable species (see the blog how to grow wildflowers). The burnet moth feeds on birds-foot trefoil and is day-flying, unlike many moths. It lays its eggs on grass or flower stems and they hatch out in June and July. Their bodies contain cyanide obtained from food plants, so birds will not attack them. The fact that they have bright markings is a warning to their predators in the same way as the colouring of ladybirds which are similarly chemically protected.

Cinnabar moth caterpillar

      An equally poisonous insect (though not to humans unless you happen to eat moths) is the cinnabar moth and this looks similar to the burnet. Its caterpillars are remarkable because their colouring looks a bit like a rugby shirt. They can be seen in large numbers on ragwort, a plant which should not be encouraged as it is poisonous to horses, damaging their livers and causing a painful death. For this reason it is classed as a noxious weed and should be removed and destroyed. However, it is so common that complete eradication would be an impossible task, so it can commonly be seen in the countryside and motorway embankments - probably a good thing for the cinnabar moth which is so reliant on it. It seems that a horse wouldn't eat the plant in its normal growing state - the danger occurs when grass including some ragwort has been cut and left lying, causing the animal to mistake it for hay.

Common blue butterfly

Common blues mating

      The common blue butterfly uses birds foot trefoil (pictured further up the page) as a food plant - further encouragement to introduce some among the crazy paving, where it will attract a number of different insects. The addition of a herb bed is also a magnet for insects, and is to be highly recommended to the gardener who demands more than just a pretty, hygienic display.

      There's a lot more than you may think to be enjoyed in the countryside and the garden - it's just a matter of learning how to look.