Question: Wikipedia article on rectal spiders.

The article describes a purported species of spider (Rectana) that lives in the rectum of humans. Rectana are described as being between 1.5 and 2.5 mm in length, with black bodies and white legs.

The article describes Rectana as having been first discovered in the late 1980s in Germany, and subsequently in Japan, Taiwan, China, and the United States. It is stated that the spiders are found in the rectums of 30% of people. Rectana are said to live in the rectum for up to 20 years, and to cause the victim to experience "abdominal pain, nausea, constipation, and vomiting".