You can know if you have worms by observing some common symptoms and performing specific diagnostic tests. For example, if you have threadworms (pinworms), the most common symptom is an itchy bottom, especially at night when the worms lay eggs around the anus. You might see small white thread-like worms around the anus or in your stool. For diagnosis, your doctor may use a "sticky tape test" where tape is pressed around the anus first thing in the morning to collect eggs for microscopic examination. Other worm infections might cause symptoms like diarrhea, abdominal pain, tiredness, weight loss, or anemia, and are diagnosed by stool sample tests or blood tests.

Other signs may include skin rashes shaped like worms, fatigue, poor digestion, unexplained weight loss, or seeing worms in vomit or stool. If you encounter symptoms such as blood in stools, persistent vomiting, or severe abdominal pain, you should see a doctor for proper diagnosis and treatment.

In summary:

• Itchy bottom (especially at night) for pinworms
• Visible white thread-like worms around anus or in stool
• Abdominal pain, diarrhea, nausea, or weight loss
• Skin rashes shaped like worms
• Fatigue and poor appetite
• Use of tape test or stool sample for diagnosis

If you suspect a worm infection, medical consultation and testing are recommended for accurate diagnosis and treatment.