How are black widow spiders harmful to humans?

The bite of the Black Widow Spider is harmful, although it is not usually fatal to a healthy adult human. During the first 24-hours, a bite can cause severe muscle pain and cramping, headache dizziness, tremors excessive sweating, nausea, vomiting, anxiety, fatigue, insomnia, tearing of the eyes, joint pain, too rapid or too slow heart beat, restlessness and elevated blood pressure, among other problems. The muscle spasms, tingling, nervousness and weakness can last for months. Anyone who thinks he or she may have been bitten by a Black Widow should seek medical attention immediately.