Did you realize that it’s possible to have tiny creatures living inside of you? Does that make your skin crawl? If it does, that’s OK! Most people don’t like the thought of being a home for invisible little creatures that can cause harm.

What are we talking about? Parasites! Parasites are tiny organisms that get their food and shelter from other organisms. Sometimes that other organism might be YOU. If so, the parasite calls you its host.

How can you get parasites? Many parasites are transmitted by food or water, dirt or waste and even person-to-person contact. Most parasites are tiny. They can range in size from single-celled organisms that are invisible to the naked eye to larger, multi-celled organisms that can be seen without a microscope.

Parasites rely on their hosts for food and shelter. Unfortunately, they also cause their hosts harm. For example, some common parasites are viruses. Viruses, like all parasites, rely on their hosts to live, grow and reproduce.

In the process, they also often make their hosts sick. Fortunately, it’s rare for parasites to kill their hosts. They can, however, causes diseases, malnutrition and many other types of illnesses.

Children can often transmit parasites quite easily between themselves and other children. Whether they’re in school or daycare, children seem to have a knack for sharing things, including cold germs and parasites.

According to the Centers for Disease Control and Prevention, some of the most common parasites in children include giardia, pinworms and head lice. Luckily, most parasites can be easily treated with modern medicines. Once parasites are identified, they can be treated and stopped in their tracks before they’re passed along to others.

Giardia is a tiny organism called a protozoa that lives in the intestines of humans and animals. It’s often transferred via contaminated water. Giardia infections often lead to painful stomach cramping that can last up to six weeks.

Pinworms are just what they sound like: tiny, thin, white worms that can grow to be up to a quarter-inch long. They are often transferred via dirt or waste. As many as a third of all children around the world may have pinworms at one time or another. Although they can cause a variety of illnesses, they can be killed easily with medication.

Head lice are perhaps the parasite children are most familiar with. These tiny insects live in the hair and feed on blood taken from the scalp. Lice spread easily between children, because the insects have claws that help them crawl and cling firmly to hair, clothing and combs. Lice can cause irritation and infections, but they can be treated with special shampoos.

Giardia, pinworms and head lice are not the only parasites that affect humans. There are many more, including roundworms and tapeworms. How can you avoid parasites? Take care of yourself, stay clean and wash your hands frequently!

57 Join the Discussion

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    • Hi there Alexis, sorry if we made your skin crawl with today’s Wonder! We are not a fan of parasites either, but we like learning about them and what they do! Have a SUPER day, Wonder Friend! :)

    • Hey Joseph, thanks for learning something new with us today!! We are glad you enjoyed our creepy crawly Wonder, too! Also, we hope you have a special cricket recipe that you can share with us– we are so interested in learning about your cricket breakfast!! :)

  1. Yahoo! First one again! And, what?!?! Parasites!! Like almost every single people have it all around the world!? I think not, ok mabe a little, but how can people get the ppp-Parasites! And, how can a tiny thing cause a gigantic problem? :-( :-P

    • Hey there Carlos, we are so glad you’re here! We can’t believe all the interesting things we’ve learned about parasites in today’s Wonder!! They are little creatures with big power! We can’t wait to Wonder with you again– have a WONDERful day! :)

  2. I learned so much and more things today. Did you know that it’s possible to have tiny creatures living inside of you? Although they can cause a variety of illnesses, they can be killed easily with medication. Giardia, pinworms and head lice are not the only parasites that affect humans. There are many more, including roundworms and tapeworms. How can you avoid parasites? Take care of yourself, stay clean and wash your hands frequently! How do you think these crazy little bugs get in my body? It is a little strange that bugs live inside you!! I think tomorrow’s wonder may be about space and rockets in space and maybe there is a new planet who knows. Will just have to wait to see tomorrow. Can’t wait to wonder again.


    • WOHOO, Jules you have done a SUPER job summarizing the insect Wonder today! We like that although bugs aren’t always our favorite, they are really interesting to learn about and can have an effect on humans if they are not handled correctly. Great job on providing tips for staying healthy and parasite-free! We are so happy to see you today, and we can’t wait to find out what tomorrow’s Wonder is either! See you soon! :)

    • Hi there Sarra S! We are SUPER excited that you are joining us as we Wonder about those small but mighty parasites! Even though we can’t always seem them with our own eyes, it’s so interesting to learn about where and how they exist! Thanks for being a great Wonder Friend– we will see you soon! :)

  3. Wow I feel so unhealthy right now. I learned that parasites could come from anywhere. Dirt, water, and food and other every day objects. Also I learned that it is fairly easy to treat peaole who have parasites. With new medicine and other medical things. I have also found out that it is not favoriable to be killed by a parasite. Is it posable to get parasites from the air? I think tomorrow’s wonder is rope.

    • Fear not, Matt D! Although parasites are everywhere and not the easiest to spot all the time, you can avoid them on a regular basis with proper hygiene. Medicine is also available and helpful if you do encounter those pesky parasites! We are glad you’ve learned something new, even if it’s a little bit creepy and crawly. We can’t wait to catch up and Wonder again! :)

    • Hi Siddman, we’re glad you commented on our parasite Wonder! Even though parasites aren’t always the easiest thing to talk about, we’re glad you’ve been WONDERing about them. It’s cool to learn about the connection between parasites and other organisms, too, just like Mrs. Caplin mentioned! Have a SUPER day and we’ll see you soon! :)

  4. Hi! I’m in Mrs. Caplin’s class. I thought that this wonder was kind of creepy. Can’t parasites become extinct? Smallpox is gone, and so are many others.
    I thought the video was weird. The snail looked so small and pitiful. The pulsing thing inside it look like a caterpillar with neon lights. Cool Wonder!
    :) :)

    • We really appreciate your comment about the parasite Wonder, Mookie the Cat! We know that parasites aren’t the most heartwarming thing to Wonder about, but we are so glad you are! We like that you’re thinking of other parasites that have contributed to diseases and viruses, too! Way to go!

      Thanks for WONDERing with us about these crawling critters, and we hope you do some more WONDERing of your own about other diseases that are no longer an issue. Great work, Mookie the Cat! :)

    • Hi there, Anna! Thanks for WONDERing with us today– we are so proud that you checked out our Wonder, even if it made your skin crawl! We hope you learned something new about parasites and how you can stay away from them, too! We think you have a great guess for tomorrow’s Wonder… we hope you like it! Giddy up! :)

  5. Dear wonderopolis,

    Though today’s wonder was a bit disturbing, it was VERY interenting! I did understand a lot of the video and the article, but i did have some questions.

    1. How does the bird spread the parasites?
    2. How long would it take before the parasites take over your body?

    That’s all! Thanks! I’m really looking forward to tomorrow’s WONDER OF THE DAY®!
    :D :P :D

    P.S I was a part of the 6D class.
    (On “what’s your favorite breakfast cereal?”)

    • Hi there, Narwhal, we are so HAPPY you’re WONDERing with us today!! Our parasite Wonder makes our skin crawl a little bit, too– but don’t worry, we are glad you’re learning with us! You have some SUPER questions, too, Narwhal!

      Birds are able to spread parasites with their special ability to fly. Because they can travel so far, they are able to take parasites from one place to the next– across the country when the migrate, too!

      You can check out Wonder #144– “Do All Birds Fly South in the Winter?” for more information!

      We Wonder if you can do some research of your own about parasites and humans. We bet you could learn a lot about how to avoid them and what they like in humans, too! Thanks to you and all your Wonder Friends in 6D class for joining us!! :)

    • Thanks for sharing your comment, Grace– we really appreciate your thoughts and value your opinion. We are so glad you like visiting Wonderopolis– we love great Wonder Friends like you! :)

    • Hello Ava and Nick! We know that parasites aren’t the most cuddly creatures, but we’re glad that you are still WONDERing with us as we learn about parasites. We can’t wait to uncover tomorrow’s Wonder with you… what you find underneath it might surprise you! :)

    • YIPPEE, we like your enthusiasm for parasites, Eric! They are not the friendliest insects, but they sure are interesting to Wonder about! :)

    • WOHOO, Eric, we love your enthusiasm! Science is so much fun, especially when you can relate what you’re learning about to your every day world! If you have a pet, you may already be familiar with parasites. Keep up the SUPER WONDERing, Eric! :)

  6. I have a lot of pets I have a dog, three bull frogs, two snails, 20 small fish, a huge spider named arena, and one crab. But it is mostly because my Dad is a science teacher you know that is why I have so many pets and why I love science. (He teaches seventh grade)
    :) Farewell

    • WOW, you are such a lucky duck, Eric! It sounds like all your pets get along great– they are part of the family! :)

      We are so glad you enjoy learning about science as much as we do– we think WONDERing about science is SUPER fun! HOORAY for using our imaginations today! :)

    • Hi Angel, we think it’s great that you’re overlooking your dislike for bugs while you continue to Wonder about them! You are a true Wonder Friend– nothing is stopping your imagination! WAY TO GO! :)

    • Not to worry, Seddy, we think it’s tough to overcome the sliminess of parasites, too! But you did a great job WONDERing about them! WAY TO GO! :)

    • Hi there Kaitlyn, we know parasites aren’t the most cuddly thing to Wonder about, but we’re glad you’re here! Ringworm is a skin infection. Sometimes, humans can get ringworm from animals if the animal has ringworm. However, keeping your hands nice and clean by washing them frequently is important– you will do a great job of avoiding parasites this way! :)

  7. Once in summer camp someone had head lice….we were all afraid we would get them! Yuck!! My mother always says she feels very itchy whenever someone at school has them. She feels like she has them but she never does! I guess flees are parasites on animals?

    • Yikes, we think lice can be a tricky little bug to get rid of, Patrick R! Sometimes when we hear about lice, our body feels itchy– just by thinking about it! We are glad that you learned something new about parasites today– we know they are creepy crawlers, but they are cool to learn about! :)

    • How cool, John! We hope that your project is great– we are glad to know that you discovered that parasites are quite interesting! :)

    • We’re sorry to hear this wasn’t one of your favorite Wonder videos, Chrissy, but we enjoyed WONDERing about tadpoles with you. :-)

    • They there, Adrien, we are sorry to hear this Wonder wasn’t as happy as others! We know that insects can be creepy crawly, but we’re glad you WONDERed with us today! :)

    • We’re sorry to hear this Wonder didn’t make you smile like some of the others, Atira! We are very proud of you for WONDERing about a super-tiny parasite with us today! :)

    • We’re so glad you brought this to our attention, Alex. Your aunt is correct – lice cannot jump. After doing some research, we’ve updated our Wonder text with this information! Thank you for WONDERing with us and leaving this comment! :)

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Have you ever wondered…

  • What is a parasite?
  • What problems do parasites cause?
  • What are some common parasites that children might encounter?

Wonder Gallery

mosquito_shutterstock_86679493Vimeo Video

Try It Out

Ewww! Did today’s parasitic Wonder of the Day make your skin crawl? Keep the learning going by exploring one or more of the following activities with a friend or family member:

  • Ready to become a Parasite Sleuth? Learn more about where parasites live with this fun online interactive activity. The more you know about parasites, the easier it is to avoid them!
  • We know parasites are kind of gross, right? But, hey, some kids love learning all about the gross things in the world around them! If you’re one of those kids, we recommend you check out the Parasite Picture Gallery to see pictures of some of these creatures. If you get grossed out, though, don’t say we didn’t warn you!
  • Up for a challenge? Can you pick out and take care of your very own parasite? Check out So, You Want a Pet Parasite? You’ll be able to learn more about certain parasites and how they make a home inside of YOU!

Still Wondering

National Geographic Xpeditions’ Insects We Love and Hate lesson teaches children about some insect parasites, such as mosquitoes and lice.

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