Which of the following is NOT a characteristic of true flies?

True flies, belonging to the order Diptera, are distinguished by several key characteristics. One of their defining features is that they possess only two wings, which is a significant aspect of their biology. The front pair of wings is functional and used for flight, while the hind wings have evolved into small structures known as halteres, which help with balance and orientation during flight.

Another important characteristic of true flies is that they undergo a complete metamorphosis. This involves several distinct life stages: the egg, larva, pupa, and adult. This complex life cycle allows for different ecological roles and adaptability to various environments.

In contrast to these characteristics, true flies do not have three body segments. Instead, they typically have three primary parts: the head, thorax, and abdomen. While the thorax is segmented, it doesn't count as a distinct body segment like the head and abdomen when considering the general anatomical structure. Therefore, the key point is that true flies are characterized by having two wings, halteres, and going through metamorphosis, rather than having three body segments.