The short answer is that leeches need blood to grow and reproduce. Blood is a good food source for them, and they may only need to feed once a year. Leeches are not the only animal that feeds on the blood of animals. Others include mosquitoes, ticks, vampire bats (yes they exist, but only in South America), bed bugs, lice, other insects and the lamprey fish. All these feed on larger animals – but don’t kill them, so they are all called parasites. leeches have been used to treat human diseases for thousands of years. However, we now know that allowing leeches to suck blood does little to help in most cases.

Key Takeaways:

  • Leeches suck blood for food and to help in reproduction.
  • When leeches bite and begin to suck blood, they are able to release chemicals that prevent a blood clot from forming.
  • Leeches were once more prevalent as a medicinal tool and while there are still things to learn, they don’t play as important a role in modern medicine.

“Parasites all live on or in other animals and many of them feed on blood. Blood is easy to collect whether you are inside or outside the body. It is highly nutritious and there is always lots of it, so the animal the parasite is feeding on can usually spare some.”

Read more: http://theconversation.com/curious-kids-why-do-leeches-suck-our-blood-117316