What characteristic distinguishes the black widow spider?

The distinguishing characteristic of the black widow spider is that the females guard their egg sacs and are the most dangerous. Female black widow spiders are known for their potent venom, which poses a significant threat to humans. They are recognized for their glossy black bodies and the distinct red hourglass marking on their abdomens, making them easily identifiable. The behavior of guarding their egg sacs is crucial for the survival of their offspring, as the eggs are vulnerable to predators and environmental conditions. This protective instinct highlights the role that female black widows play in the reproductive success of their species, further emphasizing their importance in the life cycle of these spiders.

The other options may contain facts about different types of spiders or inaccuracies regarding the black widow. For instance, while some spiders may have brightly colored markings, the black widow's identification mainly comes from the specific color pattern of the female that sets it apart. Similarly, the laying of eggs typically occurs in silk sacs in sheltered environments rather than in water, and black widow spiders do not have lifespans of 10 years; they usually live up to a few years, depending on conditions. Thus, option B accurately captures crucial behavioral information specific to the black widow spider, illustrating both its danger and nurturing instincts.