These days, there is an eager debate about whether or not there was room for all the animals on Noah’s Ark. We will not interfere in the scholarly debate but simply point out that there indeed exists a very large number of animal species. Today, roughly one million different animals are known, and studies of tropical forests suggest that the actual number could be much higher – perhaps 20-30 million. Most are insects and mites. With few exceptions, these are animals, which perform useful work in nature and are harmless to us. Some animals may bite, sting and cause skin symptoms in humans. Most of these kinds of animals live in the tropics. The few species that live in Denmark are not particularly dangerous and these are what this book is about