In many cases, the biting or stinging insect has not been seen. They may be operating in the dark or are so small that they are hard to spot, and it would be nice if the symptoms alone could determine which species did the biting or stinging. Unfortunately it is not that simple. The itchy bumps of the type that most of us know from mosquito or flea bites are an allergic reaction, and each person responds very differently. This also applies to people in the same family. Some may not respond to bites of a certain type, while others swell up violently. It may add to the confusion, that the time it takes for the skin to reaction can vary from person to person. Some people respond immediately, while others respond after a few days after being bitten or stung.

It is common that there is an immediate reaction to a sting or a bite; however, often this reaction wears off within an hour. Several hours later – up to a day – at the same place, as a delayed reaction, the typical itchy “mosquito bites” appears and can itch for several days or weeks.

Finally, the old bite or sting can suddenly, for reasons unknown, start to itch again several weeks after it has settled .It is practically impossible to distinguish between bites of, for example, bedbugs, mosquitoes and fleas, however, the location of the bites may be an indication. Bed bugs and mosquitoes do not like to crawl under clothing or blankets. Their bite is therefore mainly seen on the parts of the body that is uncovered at night. Fleas on the other hand preferably bite the lower legs, under tight clothing and similar places. Flea bites are usually in groups of 2-3 bites right next to each other.

Itching is a nonspecific symptom that is sometimes caused by small animals. When experiencing itchy scalp hair, it is natural to look for lice. Itching between fingers and wrist may be the work of itch mites, handling mite infected goods or something else entirely. When the pubic hair itches, pubic lice are definitely an option.
Things that are inhaled may cause asthma and rhinitis. Of the animals mentioned in this book, dust mites and storage mites are known for causing these symptoms but there are many other options.

The blood-sucking animals can infect humans with bacteria, viruses, fungal spores and unicellular animals. From what we know so far, the caster bean tick is the only transmitter of infectious agents in Denmark. In the other Scandinavian countries mosquitoes are suspected of passing summer flu virus, etc. on to humans. The problem is that although these viruses can be found in mosquitoes, there is a lack of evidence that mosquitoes actually transmit the infection.