Monday, 1 May 2006

Norfolk's Tiger

Last week, drawn by the sun’s warmth, I made a visit to Thetford Warren Lodge. This splendid example of a dry lichen heath has been somewhat spoilt by litter, left by some of Thetford’s more ignorant inhabitants. Fortunately, such people are also lazy and once you move away from the car park, the litter ceases and the heath is relatively untouched.  I had come in search of a number of creatures, all of which I hoped would also have been brought out by the sun. Common lizards were much in evidence; some proving to be approachable as they basked but many others disappearing rapidly into the vegetation. Bare patches of sand were alive with spiders and solitary wasps, while queen bumblebees and brimstone butterflies were on the wing.

Alongside these were green tiger beetles, a common and widespread species of heath and moorland, and one of my all-time favourite insects. The green tiger beetle is one of five related species to be found in Britain. All the others are rather scarce and localised in their distribution, with only one of them occurring in Norfolk. This is the dune tiger beetle, found at a handful of sites along the North Norfolk coast and a species I have yet to see. Both species breed in early spring, their larvae inhabiting vertical burrows in the sand from which they ambush passing prey.

Tiger beetles are difficult to approach, especially on open ground, as they take flight readily and have excellent vision. As I approached, each one would rise up into the air and make a short buzzing flight before dropping to the ground some 15 or 20 feet further away. In flight, they sparkle jewel-like, as the light catches their extremely shiny purple and green undersides. On the ground, and viewed from above, they are equally striking: leaf-green wing cases, marked with pale cream spots, cover the abdomen. The green extends forwards across the thorax and up onto the head, where two large eyes sit above a cream white face and a fearsome pair of jaws. Long-legged and well-equipped, this is a predatory species that relies on speed to catch smaller prey. Interestingly, tiger beetles digest their prey externally by excreting the enzymes needed to break the prey down before sucking up the resulting semi-fluid remains. To be able to do this tiger beetles have highly specialised mouthparts, with some parts fused together to form a powerful sucking pump. I was surprised when I discovered this fact and, if honest, also a little disappointed. I’d always imagined that such a fearsome predator would use its large jaws to tear its prey apart in much the same manner as its mammalian namesakes.

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