What is a key difference between hard ticks and soft ticks?

The distinction highlighted in the correct answer is fundamental in understanding the differences between hard ticks and soft ticks. Hard ticks belong to the family Ixodidae and are characterized by their tough, shield-like structure on their dorsal side, known as the scutum. This hard outer layer gives them a different appearance compared to soft ticks, which belong to the family Argasidae and possess a more flexible, leathery body without a scutum. This key anatomical feature reflects their evolutionary adaptations and influences their behavior and feeding habits.

The other choices present inaccuracies regarding ticks. For instance, hard ticks do not possess modified wings, as ticks are arachnids and not insects. Soft ticks are not limited to invertebrate hosts, as they can also feed on various vertebrates. Lastly, classifying hard ticks as insects is incorrect since they are part of the arachnid class, which includes spiders and scorpions, and this group is distinct from insects. Understanding these differences is crucial for anyone studying tick biology and their role in disease transmission.