Nature 2008 February

Spinning a tale or two about the web of life

Difficult to believe in a year when there was no summer to talk about, but 2007 was the third warmest on record, only edged into bronze place with 1998 in gold and 2005 in silver. Despite this, 2007 also proved to be the wettest so far this decade (circa 33 inches fell locally). Whereas Britain suffered major flooding in 2007 we were lucky to escape most of the deluge in July, which luckily fell mainly elsewhere. In fact this increased rainfall has been a significant feature of the last 18 months or so and has led to a dramatic rise in the local water table, which rose to over 50 feet by April: its highest point since 2001. As the water table has remained high going into 2008 and with the medium-term meterological forecast suggesting a wetter than average first quarter, I anticipate that we may see the seasonal chalk streams and bournes spilling out lower down the ‘vales’ and as in 2001/2 once again putting pressure on Chesham’s flood management.

There are over 640 species of spiders in Britain and 100 of these can be found in our gardens and around a dozen more living amongst us indoors. Early morning dew bedecks the webs of garden spiders. It is only the female who constructs these traps. The male scavenges for food rather than producing these elaborate structures. The webs are built twice, the first time a non-sticky framework, which is tensioned with stout strings. When the second web is spun it starts as a fine spiral on the central section of the web. This is where the spider will await its prey. Meanwhile the outer sections are then re-spun using sticky gummed silk produced by a special gland and entwined by three spinnerets on the spider’s abdomen. The non-sticky strands of the first web are eaten as it goes. To avoid getting tangled, the spider spreads special oil liberally over its legs. Not all spiders produce elaborate webs. Some lay their sticky strands across the grass in a mesh; others produce funnels or ‘spit’ a sticky net at their prey. For the spider this is a web of life, for its prey a web of death!

Cock pheasants are prone to causing a disturbance day or night at the moment as they patrol their territory, ensuring their harem of hen birds are not wandering off. Occasionally, a younger male ‘on the make’ will try and muscle in and this will set-off one or more controlled couplets of clucks. Where the encounter is with a deer, human or predator, rather than a cluck it’s a cacophony. More distinctive though are the wing beats of the defending male as he drives the upstart off. Whereas we hear this as the drumming, it is not so much the noise but a low frequency vibration, too low for our ears, which resonates for several miles around and signals to other contenders to keep away. Other ‘game’ birds such as grouse and quail have their own distinctive signature tunes. Perhaps most unusual is the snipe, a wading bird much persecuted as ‘game’ in earlier years, which I recall hearing as a youngster as its booming sound bombarded my ears causing me some discomfort.

Populations of these game birds are subject to many ups and downs. Typically, this is the result of being both reliant on a reliable and constant supply of invertebrates, grain and grass or in the case of pheasant all of these. On the other hand, healthy populations of ‘game birds’ support many predating animals – fox and stoat, or bird – sparrow hawk, peregrine and jay, or reptile – grass snake, which like the jay, happen also to take eggs. This web of life is complex. So fluctuations in the population of ‘game’ birds have an impact on those above and below them and vice versa.

Early morning – the hour before dawn – the airwaves are the province of blackbirds, chaffinches, starlings and thrushes. Blackbirds having made the running during January although due for a comeback in March, fall silent in February leaving the way clear for Mavis (the thrush) to rehearse any one of over 100 tunes it has in its extended repertoire. Meanwhile, starlings freed of their autumnal murmurings will be heard to whistle as they seek out a cranny (or nook). Chaffinches start hesitantly but when others have had their say are still going strong, finishing with a flourish. The mellow laughter or ‘yaffing’ of green woodpeckers in flight can be heard. The key to breeding success for such birds will be the availability of invertebrates. Warmth encourages the early emergence of sugar-rich flowers such as celandines, the ninepetalled stars bursting through their leaves, garlic, and in these milder days, cow parsley. In early March, there is the annual flourish of blackthorn, the pungent whitewash marching at the double along the lanes from Chesham, Tring and Wendover taking perhaps a fortnight to reach the hilltops. Without this sugar-rush there will not be an explosion of flies and bugs to provide the source of carbohydrate essential if these birds are going to have sufficient energy to propagate. This web of life is fragile. No warmth, no flowers, wet grass means plenty of worms and ground beetles, meanwhile a sharp frost and bug and bird alike are sunk.

On warm March days look out for the sulphur-winged brimstone butterflies emerging from hibernation, normally but not always ahead of small tortoiseshells. Our mild winters now support overwintering red admirals hitherto delayed abroad until the first favourable continental winds. However, a forestalled spring and shortage of suitable nectar-producing flowers will mean fewer eggs are laid and therefore less predation of the food plants. The web of life is selfregulating. So in good years an excess of caterpillars will consume all the food leading to shortages later in the season.

Some of you may have heard Sir David Attenborough last month launching the 2008 Year of the Frog campaign aimed at raising awareness of the fragility of the populations of frogs due to industrialisation, pollution, deforestation, climate change and in particular a newly discovered disease which is affecting certain populations around the world. Frogs are unsurprisingly not at the top of most people’s list of favourite animals. However, without them many pests of our cereal crops such as slugs, or beetle larvae and, further afield, locusts would be uncontrolled. Alongside spraying and inoculation they are the principal control for mosquitoes and the spread of malaria. The campaign is not aimed at changing their celebrity status but is more about raising their importance for conservation purposes and the crucial role they play in the web of life.

So next time you happen on a glistening spider’s web, think about the metaphor it portrays. A delicate inter-connecting weave of plants and animals whose ecology is balanced on thin threads which are easily damaged.