Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
A popular myth regarding human sexuality is that men think about sex every seven seconds. In reality, there is no scientific way of measuring such a thing and, as far as researchers can tell, this statistic greatly exaggerates the frequency of sexual thoughts.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
According to urban myth, the daddy longlegs spider (Pholcus phalangioides) is the most venomous spider in the world, but the shape of their mandibles leaves them unable to bite humans, rendering them harmless to our species. In reality, they can indeed pierce human skin, though the tiny amount of venom they carry causes only a mild burning sensation for a few seconds. In addition, there is also confusion regarding the use of the name daddy longlegs, because harvestmen (order Opiliones, which are not spiders) and crane flies (which are insects) are also known as daddy longlegs, and share (also incorrectly) the myth of being venomous.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Poinsettias are not highly toxic. While it is true that they are mildly irritating to the skin or stomach and may sometimes cause diarrhea and vomiting if eaten, an American Journal of Emergency Medicine study of 22,793 cases reported to the American Association of Poison Control Centers showed no fatalities, and furthermore that a strong majority of poinsettia exposures are accidental, involve children, and usually do not result in any type of medical treatment.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
The flight mechanism and aerodynamics of the bumblebee (as well as other insects) are actually quite well understood, in spite of the urban legend that calculations show that they should not be able to fly. In the 1930s a German scientist, using flawed techniques, indeed postulated that bumblebees theoretically should not be able to fly, although he later retracted the suggestion. However, the theory became generalized to the false notion that "scientists think that bumblebees should not be able to fly."

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Sharks can actually suffer from cancer. The myth that sharks do not get cancer was spread by the 1992 book Sharks Don't Get Cancer by I. William Lane and used to sell extracts of shark cartilage as cancer prevention treatments. Reports of carcinomas in sharks exist, and current data do not allow any speculation about the incidence of tumors in sharks.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
It is not harmful to baby birds to pick them up and return them to their nests, despite the common belief that doing so will cause the mother to reject them.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Bulls are not enraged by the color red, used in capes by professional matadors. Cattle are dichromats, so red does not stand out as a bright color. It is not the color of the cape that angers the bull, but rather the movement of the fabric that irritates the bull and incites it to charge.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Evolution does not claim humans evolved from monkeys, chimpanzees or any other modern-day primates. Instead, humans and monkeys share a common ancestor that lived about 40 million years ago. This common ancestor diverged into separate lineages, one evolving into so-called New World monkeys and the other into Old World monkeys and apes. Humans are part of the Hominidae (great ape) family, which also includes chimpanzees, gorillas, and orangutans. Similarly, the common ancestor of humans and chimpanzees, which lived between 5 and 8 million years ago, evolved into two lineages, one eventually becoming modern humans and the other the two extant chimpanzee species.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Evolution is not a progression from inferior to superior organisms, and it also does not necessarily result in an increase in complexity. A population can evolve to become simpler, having a smaller genome, but devolution is a misnomer.