Unlike many small mammals, the hedgehog has little to fear from predators. A rolled up prickly ball is an excellent deterrent! In the UK, the greatest predator to the hedgehog is the badger. It's excellent sense of smell enables it to successfully find hibernating hedgehogs in winter. It has an almost unique ability to uncurl them by digging its claws into the small opening in the ball's underside and pulling it open to reveal the hedgehog's vulnerable belly - which is not protected by spines.
The only other serious threat to hedgehogs are foxes, as they can be quick enough to attack the hedgehog before it has time to curl up. Generally, foxes only go for sick or young hedgehogs as well as those that are already dead. Other predators that mostly unsuccessfully go for hedgehogs are polecats, and tawny owls.
Most hedgehogs killed by natural causes die during the winter months. Badgers are responsible for some of these deaths, the rest predominantly die because they have insufficient fat reserves to last through the winter. This is a major problem with young hedgehogs, especially those born late in the summer - as they have little time to get their body weight about 600g before hibernation.
Excessive heat can be just as harmful to the hedgehog as the cold winters that it hibernates through. The hedgehog is vulnerable to heat only in warm climates and when in captivity. The problem results from the fact that it can only sweat from the regions of its body that are not covered in spines. Therefore in hot weather, a hedgehog will spread itself out flat on its back to allow as much heat loss as possible - while making it more susceptible to predators.
Manmade hazards are the major causes of hedgehog deaths in the UK. As human populations have increased, hedgehog habitats have been destroyed. Not only are the hedgehogs made homeless, but they are also faced by a shortage of food. Where hedges are now found, so are roads and farm machinery. The once safe haven of a hedgerow for nesting is now dangerous due to the risk of being carved up by agricultural machinery in the adjacent fields. This has meant that hedgehogs are now rare in arable farming areas. Intensive farming also provides another assault on the hedgehog - increasing amounts of pesticides and other chemicals are sprayed on crops. These are often aimed at the hedgehog's pray - and so the chemicals are transmitted through the food chain. When combined with air and water pollution, this toxic mix will accumulate in the hedgehog and they may prove fatal.
Hedgehogs are particularly accident-prone. The amazing skill that the hedgehog has of expertly falling into things is compounded by a number of man-made devices. Hedgehogs can fall through the bars of cattle grids on farms and find themselves unable to escape. Farmers are encouraged to place a ramp in the pit to allow hedgehogs to escape, and so prevent them from starving to death. Similar accidents can happen in garden ponds. Despite the hedgehog being able to swim, it will often drown because steep sides made from slippery materials prevent it from climbing out. The same solution of erecting a ramp leading out of the water is suggested.
Gardens can be particularly dangerous places for hedgehogs. Drains can trap hedgehogs if the cover is removed, and buried dog loos can become traps - with the added danger of poisoning. Slug pellets are also poisonous to hedgehogs - whether eaten directly, or or consumed indirectly through eating poisoned slugs or drinking contaminated water supplies. Hedgehogs can easily become tangled up in any kind of discarded netting - including that used to keep plants under control, and birds off fruit bushes.
Hedgehogs are also killed by the direct actions of humans. Garden strimmers are becoming one of the leading causes of hedgehog casualties - and the injuries are usually severe with whole limbs or worse being chopped off. These terrible injuries can easily be prevented by always checking long grass for hedgehogs before starting. Hedgehogs will nest in compost heaps, haystacks and bonfires. Hedgehogs are often injured by garden forks being stuck into a pile of leaves and you should always check bonfires for nesting hedgehogs before lighting them - especially as hedgehogs will be starting to hibernate around bonfire night.
More shocking is the deliberate killing, maiming and trading in wild hedgehogs. While the hedgehog is generally welcomed by the gardener, it is not by the gamekeeper. It is accused of eating the eggs and nestlings of some game birds. Some gamekeepers control the number of hedgehogs on their estates sometimes killing hundreds in a single year. In the 18th century, some parishes paid a bounty for each hedgehog killed. The hedgehog actually only occasionally takes the eggs of pheasants and partridges - and research has shown that the damage is mostly done by foxes, and that domesticated cats and dogs are more the culprits than the hedgehog is. Another deplorable act of cruelty is children playing with hedgehogs - an activity which usually involves kicking the hedgehog like a football. Although this is supposed to be illegal, loopholes in the law usually allow the perpetrators to get away with it, on the grounds that the hedgehog was technically free to walk away.
In my opinion, equally unjustifiable is the trade in wild hedgehogs as pets. Hedgehogs are taken from the wild in Egypt and can commonly be found on sale on the markets of Cairo. Even more shocking is the revelation that hedgehogs were imported into the USA supposedly for scientific purposes and were then sold as pets. Some would now justify the sale of hedgehogs in pet shops by saying they were specially bred as pets, but this is a misconception as it is the same breed of hedgehog that was poached from the wild that is being bred and then kept in captivity.
It should be emphasised that a hedgehog's instinct is to rely on its spines for protection against any threat. Therefore hedgehogs are unlikely to move out of the way of oncoming vehicles. Dead hedgehogs lying in the road cause much concern among hedgehog lovers - and much controversy too. Either it means that hedgehog numbers are being depleted by these casualties, or that the population must be vigorous to provide a continuous supply of victims. It has also been suggested that hedgehogs are gradually learning not to roll up in front of cars but to run for it. The runners survive and pass their genes to future generations. However, the 'runners' are just as likely to be squashed as the ones that roll up as they will probably find themselves in the path of one of the car's tyres. In any case, there has been too little time, in evolutionary terms, for the hedgehog to adapt its way of life to the presence of the internal combustion engine.