You Can't Feel Wet

0:00 Try this.

0:00 Put on a latex glove and then put your hand into ice cold water.

0:04 You'll notice it still feels wet.

0:08 But that's strange because the glove is impermeable to water,

0:11 but it still feels wet.

0:12 That's because we actually don't have a way to directly measure wetness.

0:15 Instead, we use temperature changes as a proxy.

0:18 And that works most of the time because

0:19 water conducts heat 23 times faster than air.

0:22 So your skin touches water, it pulls away heat,

0:25 and your brain interprets that loss of heat as wet.

0:28 And that's why 15°ree water feels a lot colder than 15 degree air.

0:32 As long as it kept us dry enough to survive and to not die of hypothermia,

0:36 this heat trick was good enough.

0:38 But not so for insects.

0:39 At these scales, water is dangerously [music] sticky.

0:42 So many insects adapted these microscopic hairs

0:45 which deform in the presence of moisture.

0:47 And this let them detect [music] water directly.

0:49 So flies actually know something we don't.