It is not just warm weather that turns a pest from a minor irritation into a problem serious enough to warrant expert help. Anyone who has left squirrels to run free in their attic will know that the damage they cause can run into thousands of pounds.
The owner of a Dorset cottage who had been aware of some scutterings only discovered the state of the wires and beams in her attic when she came to sell the house. Before she could put it on the market she had to spend pounds 3,000 on repairs. The plastic covering on wires is evidently well suited to a squirrel's dental regime.
But at this time of year, it is advisable to be especially alert, since many problems only become apparent during hot spells. This is something Elisabeth Guidot knows only too well. The common cat flea - also found on dogs - can usually be exterminated by appropriate spraying and treatment of the animal, but for the Guidots it would have been as useless as mopping up floodwater with a sponge.
Three weeks away from home with their dog turned her house into a breeding- ground which erupted on the family's return. "As we came in the door, the children knelt down to pick up the post and then went into the sitting- room. Within seconds they were covered in a mass of black. Fleas were jumping at us from all directions. My feet and legs were black up to my knees. We screamed and tried to shake them off," says Elisabeth.
They evacuated the house, returning the next day after the local council in west Devon had sprayed the rooms downstairs. "We had to leave it for three days and then vacuum for a few days after that. Even then we were still being bitten on our legs and back. It was revolting," she recalls. "They had to come and spray it again."
Unless a pest is persistent or dangerous, there is no reason why we cannot deal with them ourselves, although not many people would choose to tackle an infestation of rodents. Ants, flies, moths and fleas can be eliminated by any number of sprays and powders.
However, a serious infestation is generally better handled by experts. They have access to chemicals that are not available over the counter and, crucially, they know how little as well as how much to use.
Food, whether animal, vegetable or mineral, is the one factor that lures all invaders. If they are not after blood they are chomping their way through solid matter. The wood-loving termites of the West Country that hit the news headlines last year are thankfully rare, according to Tony Stephens of Rentokil Initial.
Far more common are some relatively little-known nuisances such as carpet- and fur-beetles, which have outstripped the clothes moth as the major British textile pest.
"They like anything of animal origin, particularly cashmere, and will browse around carpets picking out the wool. They tend to wander along pipes from roofs into airing cupboards, and the next thing you know you have T-shirts that look like string vests," says Mr Stephens.
Of all the hundreds of beasts and bugs that invade our homes, the rat disturbs us most. Not only verminous and fecund, they are intelligent, too.
Jessica Berry met one face to face in her basement flat, and considered it an emergency. "I went to the loo and lifted the cover. As I leaned down an enormous brown rat leapt out at me. I ran screaming from the room and went straight to the Yellow Pages to look for emergency pest-control.
"I was hoping someone could come immediately, but all it means is that the phone is answered for 24 hours. It was two days before anyone turned up. In the meantime, I put the bathroom scales on top of the toilet cover and left them there," says Jessica.
"When the council came they found a large nest, about five metres below the kitchen floor where the main drains ran. The rats were getting in through a disused drain hole, and once that was covered up I never saw them again. But I had to have my floor ripped up, at my expense, for the nest to be destroyed. One problem was discovering who was responsible for dealing with it - the local authority or the water authority."
At least the work was not in vain. Jane Williams was selling her house, in the summer, when she noticed a terrible smell. With viewing due to start, she arranged for a plumber to check the drains. The next day the smell had moved. It was particularly strong in one corner, where she finally found the culprit - a bag of prawns that a friend had left behind by mistake.
British Pest Control Association: 01332 294288; Rentokil: 01342 833022