Moth and bat coevolution is a classic example of the intersection of behaviour and neurology. Bats locate their prey through echolocation, a process by which a bat emits ultrasonic waves and uses the reflection of the sound to locate itself in space and to find food. Bats have to eat at least once an hour to support their metabolism and so there is strong selection for bats that can echolocate efficiently. Similarly, moths are under heavy selection pressure to avoid becoming food. To sense the direction of their bat predators, noctuid moths possess two sensory nerves connected to their tympanum. The A1 nerve fires more frequently as ultrasonic sound gets louder and the A2 nerve only fires when ultrasonic sound is particularly intense. Each side of the moth thorax has a tympanum and its complementary pair of nerves. This allows the moth to determine the direction from which the bat is approaching. If the sound is louder on the right side than the left, then the moth knows the bat is coming from the right side. If the sound is louder when the moth has its wings up and softer when its wings are down, then the bat is coming from above. Within the three metre echolocating range of the little brown bat, its primary predator, the noctuid moth can sense the direction from which the bat is arriving and attempt to fly away from it. Should the bat get too close, the A2 nerves will fire causing the moth’s wings to beat out of sync and engaging the moth in a spiraling power dive. During this erratic movement, not even the moth knows where it will end up, though usually it will crash land in bushes that will mask its position. This evolutionary arms race is but one of many where there are heavy selection pressures on both predator and prey.
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