It's a hard life raising crops in Australia, as farmers often remind the 85 per cent of Australians who live on the coast. Recent rains in New South Wales provided a bit of relief from the worst drought in a century, but now those living on the land face another challenge: locusts.

Swarms of the crop-munching insects are sweeping across drought- affected areas and feasting on grass and weeds sprouting at roadsides following the rain. In western New South Wales, near the country town of Condobolin, a swarm measuring four miles long by 560 feet wide was spotted last week.

The extra food could increase the number of eggs that the locusts lay, with the next generation expected to begin hatching in mid-December. That is a nightmare prospect for farmers as they prepare to harvest their crops, in some cases for the first time in several years, after successive crop failures caused by the drought.

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The Australian Bureau of Meteorology, meanwhile, is forecasting a swelteringly hot summer that will add to farmers' woes, as well as increasing the likelihood of bushfires and their ferocity. On the coast, amid rising ocean temperatures, record numbers of jellyfish have been recorded, along with giant schools of baby sharks.

The locusts have been sighted in plague numbers across large areas of New South Wales, where the state government has distributed enough chemicals to spray nearly 200 square miles on hundreds of properties. The state's primary industries minister, Ian Macdonald, said that many hoppers, or juveniles, would grow wings over the next few weeks, so it was important to control numbers before that happened. Nine locust-busting planes are also on standby to treat the swarms if they grow larger or thicker. At the moment, they are rated as low or medium density.

Mr Macdonald sought to reassure farmers, saying there was no need to panic. "We are monitoring the situation," he said. "It's important to realise that most of the state's crops are in the final stages of maturity and close to harvest, so are brown in colour. Fortunately this means they are not as attractive to locusts, which prefer green plants." He warned, however, that "anything growing at this point of time would be attacked fairly severely by locusts".

The insects are notoriously voracious, swarming through an area and consuming everything in sight, particularly green vegetation. There are stories of them eating green clothes hanging on washing lines, stripping green paint off walls or water tanks, and destroying green shade-cloth. Adult locusts can travel more than 400 miles in a single night's flight, and they lay up to 50 eggs each at one time.

This year's outbreak is forecast to be the worst since 2004, when locusts bred furiously following floods and went on to devastate crops in two states. In 2001, swarms containing 100 billion insects were recorded. Australian authorities battling the pests have sometimes been assisted by good fortune. In the past, large numbers have perished after landing in the ocean by mistake.

Mr Macdonald said: "We're calling on farmers to remain very vigilant and to keep checking their properties, because if we do get further hatching and further development of locusts, these swarms could end up quite large and pose further problems."

One farmer, Selwyn Geddes, told Country News website that he had no time to spray the insects because he was too busy harvesting. "At one end of the paddock we have sheep and at the other we have hoppers," he said.