You probably didn't realise it, but June is quite a dangerous month. Statistically, more meteorites fall in June than at any other time of the year - and 30 June is a particularly hazardous day. Since records began, 116 meteorites have plunged to Earth in June - their high season - compared with only 57 in March - their low season. At least 17 people are said to have been killed by meteorite impact.

Meteorites are pieces of rock - usually stone, sometimes metal and, occasionally, a mixture of both - which find their way to Earth from the asteroid belt, Mars, the Moon and, possibly, a few comets. They typically weigh a couple of kilograms (though this can vary tremendously) and strike the Earth with velocities usually in the range of 100 to 250 metres per second. The Middlesbrough meteorite, for example, which landed on 14 March 1881, had a terminal velocity of 126 metres per second and weighed about 1.6 kilograms. Fortunately, it did little damage but had anyone been unfortunate enough to get in its way they would not have lived to tell the tale.

The first recorded fatalities occurred in 616 BC when stony meteorites were said to have crashed into chariots killing 10 men. Two monks have been struck by meteorites: one in Cremona in 1511 and the other in Milan in 1650. In 1674 meteorites killed two Swedish sailors aboard ship. There are also reports of a wedding guest being killed in one of the Balkan states, and a child in Japan. Few such reports are well documented, and they may well be little more than stories.

Undoubtedly, people have had narrow escapes. On 14 July 1847 a 17-kilogram meteorite fell into a bedroom in which three children were asleep in Braunau, in what is now Austria. Although they were covered in debris, none was seriously hurt. Not so lucky was Mrs Hewlett Hodges of Sylacauga, Alabama, who was hit by a malevolent meteorite on 30 November 1954 causing severe hip and abdominal injuries.

There are also accounts of animal deaths. A colt in New Concord, Ohio, perished when about 30 meteorites fell on 1 May 1860, several cows were killed when a shower of stones hit Macau in Brazil on 11 November 1836, and on 28 June 1911, 40 stones fell at Nakhla in Egypt killing a dog. The Nakhla meteorite is only one of a handful of specimens that originated on Mars. To this day the Nakhla dog remains the only authenticated case of an Earthling being killed by a Martian.

Fatalities aside, meteorites - even small ones - can cause considerable damage to anything they hit. Returning to Milan, there is the case of a red-hot meteorite landing in the castle on 23 June 1525, setting fire to the munitions. Perhaps not surprisingly, nothing remains of the meteorite.

About half of all meteorites break up in the atmosphere thus increasing the chances of someone, or something, being hit. But anyone who thinks that meteorite falls are more or less evenly distributed over the Earth's surface will find that the inhabitants of the small town of Wethersfield, Connecticut, probably disagree with them.

In 1987 Roy Clarke, a well-known meteoriticist, presented a paper to the 50th meeting of the Meteoritical Society on his team's investigations of the fall of some 39 meteorites in the US between 1932 and 1982. The team was prompted to look at the damaging meteorites after two falls in the small town of Wethersfield. On 8 April 1971, a 350-gram meteorite passed through the roof of a house and landed in the living room. Eleven years later, on 8 November 1982, a second meteorite of 2.7 kilograms struck another house only 2.7 kilometres from the first. On both occasions the fire service was called and, if local reports are true, each time the same fireman found the meteorite.

In case you are thinking that these two meteorites might have been related in some way, they apparently had quite different histories. The meteoriticists could tell that from the extent to which the meteorites were shocked. Isotope analyses showed that while the first fall had separated from its parent body about 3 million years ago, the second object became detached about 50 million years ago.

Since Clarke's report, one of the most celebrated meteorites is the Peekskill meteorite, named after the suburb of New York in which it fell last October. The 10-kilogram stone plunged straight through the boot of a Chevy Malibu, turning the driveway underneath into a crater. Fortunately, the owner of the car, 18-year-old high school student Michelle Knapp, was not in the vehicle at the time. Unperturbed by her near miss, and in the true spirit of American free enterprise, she sold the $100 second-hand car, and the meteorite, to consortium led by Marlin Cilz of the Montana Meteorite Laboratory. Cilz will not say how much he paid for the meteorite, just that the price was very high. As for Knapp, she now has a decent runaround.

Quite clearly, as towns and cities expand, and as the world's population increases, the chances of a meteorite striking a person or some kind of artefact are going to increase.

All these cases involve quite small meteorites. Occasionally, however, an asteroid-sized body does strike our planet. The most famous incident in living memory happened in Siberia on 30 June 1908, when a brilliant fireball, said to be as bright as the Sun, swept across the skies of Russia and exploded 8 kilometres above Tunguska. The shock wave flattened 2200 square kilometres of dense forest and travelled around the world several times. The portable huts of the Tungus nomads were blown over, about 1000 reindeer were killed in the resulting stampede, and at the Vanovara factory, 60 kilometres from the explosion, doors were lifted from their hinges, windows shattered and pictures fell from walls. Experts still disagree whether the object was a comet or an asteroid (see New Scientist, Science, 16 January) but one thing is for certain, if such an object ever explodes over a densely populated city such as London, Edinburgh or Birmingham it will be a disaster of immense proportions.

Tunguska-size impacts are, fortunately, rare but are probably more common than experts would have believed just a few years ago. We now have a better understanding of the sort of objects, and how many there are, that linger in space near the Earth's orbit. So, although the object that struck Tunguska was large and destructive, there are numerous other bodies out there that are bigger and, potentially, more catastrophic.

I can well remember sitting in a geology lecture ten years ago, shortly after Walter and Luis Alvarez had announced that the dinosaurs had been wiped out by a massive asteroidal impact. As with all 'new' theories, very few of those present had read the Alvarez's paper or, if they had, they failed to understand that massive impacts could bring about a so-called 'nuclear winter'. The jokes started to fly and one student asked the lecturer how some creatures managed to survive.

'Perhaps they dodged out of the way,' he suggested. 'Or maybe they wore hard hats.'

So don't be a dinosaur, wear a hard hat this June.

Philip Bagnall is president of the Society of Meteoritophiles and a hard hat-carrying member of the International Tunguska Expedition.