Researchers have built a large testing arena to study why malaria-carrying Anopheles gambiae mosquitoes prefer some humans over others as prey. The scientists discovered that specific chemicals found on human skin attract the insects. Usually, visual cues and body heat draw mosquitoes to their prey at close range, however, body odour and breath can be used to track targets from afar. In addition, one individual in the experiment was identified as less attractive to the mosquitoes because of his low levels of carboxylic acids and high eucalyptol content, a substance found in many plants. These chemicals are viewed as ways to identify new potential repellents to halt the insects.