A species of venomous spider, particularly Latrodectus sp.. The bite is painful to humans, rarely fatal to healthy individuals, but can be life-threatening or fatal to infants or young toddlers. Females are marked by a red hourglass shape on the abdomen (see photo, this page, and photos in Wikipedia). Mature males are smaller, of the same black color or a dark brown, have an elongated and slender abdomen (rather than the rotund abdomen of the mature female), and are marked on the dorsal of the abdomen with small flattened diamond shapes of the same scarlet color as the female's marks on the ventral of her abdomen.