That is what happened to Lisa Jenner's seven-year-old Jack Russell, Ella, as they walked across heathland. Ella raced off into some bushes and Lisa heard her yelping in pain.

'I rushed over and dragged Ella out of the bushes,' says Lisa, 34. 'We carried on walking for a while, but then I noticed she was staggering about and her face had started to swell up. I had seen similar symptoms from a snake bite when I was in Australia, so I guessed that was what had happened.'

Lisa immediately took Ella to the vet, but by this time the dog's face was badly swollen. Ella was put on a drip and given anti-inflammatories and antibiotics to flush the toxins from the adder bite out of her system. Ella had to stay at the vet for a few days, but she made a full recovery. And thankfully for Lisa, all the treatment and vet's bills - which came to more than £800 - were covered by pet insurance.

Lisa, an assistant manager at a health club, took out cover with More Than, owned by Royal & SunAlliance, when Ella was a puppy. The policy costs about £8 a month, but Lisa says it has been worth it.

'The claim for Ella's bite was the first I've ever had to make,' says Lisa, of Ewhurst, Surrey. 'Insurance is one of those things you don't think about until you have to claim, but then you're so glad you have it.'

Monica McCormack, spokeswoman for Tesco pet insurance, says summer can be a dangerous time for pets. Last month, Tesco saw a 6% jump in claims compared with the previous month, which McCormack says was probably as a result of the exceptionally sunny weather.

'Last year our customers made more claims from July to September than at any other time. We would urge pet owners to take sensible steps to protect their from the heat,' she says. 'Other dangers can also arise in summer, such as fleas and ticks.'

If your end up with a summer ailment and you do not have insurance, helping them get well again can be costly.

Treatment for heatstroke for a dog, for example, can easily run into hundreds of pounds. Pet allergies can also cost more than £200 to treat with medication and ointments.

There are close to 15m cats and dogs in the UK. But only one in five dogs and one in eight cats is insured, according to Datamonitor's research.

Diane Gorton, 48, an electronics engineer in the aerospace industry, from Tewkesbury, Gloucestershire, was glad she had cover for her lurcher, Harry, after he swallowed a kebab of raw meat complete with the skewer during a barbecue.

Harry had to go into surgery to have the skewer removed. He was lucky not to have been more badly injured, but the bill for his operation came to £700.

'Lurchers tend to be accident prone,' says Diane, who enters Harry in agility competitions and shows. 'They run around at one hundred miles an hour and this can end in disaster. Harry has broken toes and a few years ago he broke a leg and had to have it pinned.'

Harry is insured with Pet Plan, and Diane, who has three other cross-breed dogs - Josie, Pickle and Bertie - says the policy has saved her thousands of pounds in vet bills over the years.

'I pay £20 a month to insure Harry and Pickle with Pet Plan,' Diane says. 'It has been a worthwhile expense. I don't insure Josie anymore because she is 15 and so the premium is expensive. I only got Bertie recently, but I will look to insure him too.'

There are different types of cover to choose from and prices vary accordingly. At the cheaper end of the scale, policies from direct providers such as Tesco, Churchill and Direct Line, cover your pet for a particular condition for up to 12 months, usually with a maximum claim amount, typically £3,000 to £4,000.