WEBVTT FILE 1 00:00:00.076 --> 00:00:02.400 (phone ringing) 2 00:00:02.400 --> 00:00:04.230 - Hey, it's Esther. 3 00:00:04.230 --> 00:00:05.280 What's the coolest thing 4 00:00:05.280 --> 00:00:07.890 you've ever seen outside after dark? 5 00:00:07.890 --> 00:00:11.280 Maybe it was fireworks or a full moon. 6 00:00:11.280 --> 00:00:13.170 These people are getting ready to watch something 7 00:00:13.170 --> 00:00:15.240 you can only see when it's dark. 8 00:00:15.240 --> 00:00:17.550 If you can, you might wanna pause the video now 9 00:00:17.550 --> 00:00:19.710 and turn the lights off to watch too. 10 00:00:19.710 --> 00:00:20.643 Check it out. 11 00:00:27.150 --> 00:00:28.920 Someone named Siddharth has a question 12 00:00:28.920 --> 00:00:31.350 about what's making these flashing lights. 13 00:00:31.350 --> 00:00:32.854 Let's call Siddharth now. 14 00:00:32.854 --> 00:00:35.459 (phone ringing) 15 00:00:35.460 --> 00:00:36.839 Hi Siddharth. 16 00:00:36.840 --> 00:00:38.100 - I have a question for you, 17 00:00:38.100 --> 00:00:39.513 why do fireflies glow? 18 00:00:40.350 --> 00:00:42.060 - Great question. 19 00:00:42.060 --> 00:00:45.030 Did you guess that those lights were fireflies 20 00:00:45.030 --> 00:00:48.000 or you might call them lightning bugs? 21 00:00:48.000 --> 00:00:50.310 Maybe you've even seen some in person. 22 00:00:50.310 --> 00:00:51.210 When I'm camping, 23 00:00:51.210 --> 00:00:54.150 I've watched them in fields near my tent. 24 00:00:54.150 --> 00:00:57.450 Even though they're called fireflies and lightning bugs, 25 00:00:57.450 --> 00:01:00.420 this isn't light from fire or lightning, 26 00:01:00.420 --> 00:01:02.790 it's not from light bulbs either. 27 00:01:02.790 --> 00:01:05.490 This is light you can catch. 28 00:01:05.490 --> 00:01:08.940 Up close, you can see that this is an insect. 29 00:01:08.940 --> 00:01:11.370 Do you notice how these parts look different? 30 00:01:11.370 --> 00:01:14.490 Light can shine through them, like this. 31 00:01:14.490 --> 00:01:16.800 The light shining through is actually made 32 00:01:16.800 --> 00:01:18.990 inside the firefly's body. 33 00:01:18.990 --> 00:01:22.319 Different chemicals in its body combine to make light. 34 00:01:22.319 --> 00:01:25.109 Scientists have been able to create similar chemicals. 35 00:01:25.110 --> 00:01:27.093 Watch what happens when they mix two. 36 00:01:29.670 --> 00:01:34.670 Whoa, so each light you see here is a firefly 37 00:01:35.730 --> 00:01:38.310 combining chemicals in its body. 38 00:01:38.310 --> 00:01:39.753 How amazing is that? 39 00:01:40.800 --> 00:01:43.920 You may have noticed that fireflies don't stay lit up. 40 00:01:43.920 --> 00:01:47.880 Instead, they flash their lights on and off. 41 00:01:47.880 --> 00:01:50.040 But what's all this flashing about? 42 00:01:50.040 --> 00:01:51.930 I'm curious, what do you think? 43 00:01:51.930 --> 00:01:55.140 What are fireflies doing when they flash their lights? 44 00:01:55.140 --> 00:01:57.890 Now it'd be a good time to pause the video and discuss. 45 00:02:02.970 --> 00:02:04.263 Okay, you ready? 46 00:02:05.250 --> 00:02:07.800 This is a question scientists are curious about too, 47 00:02:07.800 --> 00:02:09.840 and it's a hard one to answer. 48 00:02:09.840 --> 00:02:12.960 Fireflies don't think and act the way people do, 49 00:02:12.960 --> 00:02:15.660 and we can't really think like fireflies. 50 00:02:15.660 --> 00:02:16.860 That's why scientists start 51 00:02:16.860 --> 00:02:19.080 with what they can see and measure, 52 00:02:19.080 --> 00:02:21.510 their observations, to better understand 53 00:02:21.510 --> 00:02:23.730 what fireflies might be doing. 54 00:02:23.730 --> 00:02:25.590 When you watch a group of fireflies, 55 00:02:25.590 --> 00:02:28.050 their flashes can seem random, 56 00:02:28.050 --> 00:02:30.180 it's hard to keep track. 57 00:02:30.180 --> 00:02:32.970 But what if you focus on one firefly? 58 00:02:32.970 --> 00:02:36.300 You can see where it flies and when it flashes. 59 00:02:36.300 --> 00:02:39.059 Now, it's difficult to film fireflies in the dark, 60 00:02:39.060 --> 00:02:41.580 so we're gonna have to switch to a drawing. 61 00:02:41.580 --> 00:02:42.900 But what you'll see next 62 00:02:42.900 --> 00:02:46.083 is based on real observations of some fireflies. 63 00:02:47.010 --> 00:02:49.440 Okay, here's our firefly. 64 00:02:49.440 --> 00:02:51.810 Watch how it flashes every few seconds 65 00:02:51.810 --> 00:02:53.103 as it flies along. 66 00:02:55.680 --> 00:02:59.010 Our firefly keeps circling back to one area. 67 00:02:59.010 --> 00:03:01.680 And look, did you see the flash below? 68 00:03:01.680 --> 00:03:05.220 There's another firefly down on the grass. 69 00:03:05.220 --> 00:03:07.499 Our firefly keeps flashing, 70 00:03:07.500 --> 00:03:11.519 and now the other firefly has started to flash too. 71 00:03:11.520 --> 00:03:14.370 They keep flashing back and forth. 72 00:03:14.370 --> 00:03:16.710 Then, something new happens. 73 00:03:16.710 --> 00:03:18.389 Our firefly flies down 74 00:03:18.389 --> 00:03:20.672 and lands next to the one in the grass. 75 00:03:22.350 --> 00:03:25.889 This is something scientists have observed many times. 76 00:03:25.889 --> 00:03:29.309 A firefly flashes as it flies around, 77 00:03:29.310 --> 00:03:31.800 another flashes back. 78 00:03:31.800 --> 00:03:33.423 They flash back and forth, 79 00:03:36.810 --> 00:03:38.043 then the two meet up. 80 00:03:39.060 --> 00:03:40.230 Maybe you guessed earlier 81 00:03:40.230 --> 00:03:43.800 that flashing helps fireflies find each other in the dark. 82 00:03:43.800 --> 00:03:46.440 And you're right, that seems to be one reason 83 00:03:46.440 --> 00:03:48.420 why fireflies flash. 84 00:03:48.420 --> 00:03:49.830 Through their observations, 85 00:03:49.830 --> 00:03:51.180 scientists have also learned 86 00:03:51.180 --> 00:03:54.870 that the ones flashing as they fly are usually boys. 87 00:03:54.870 --> 00:03:57.450 Another word for them is males. 88 00:03:57.450 --> 00:03:59.790 The ones flashing back from the grass 89 00:03:59.790 --> 00:04:03.090 are usually females or girl fireflies. 90 00:04:03.090 --> 00:04:04.807 It's like the males are flashing, 91 00:04:04.807 --> 00:04:06.150 "Hey, check me out," 92 00:04:06.150 --> 00:04:08.010 and the female flashes back. 93 00:04:08.010 --> 00:04:09.516 It's like she's answering, 94 00:04:09.517 --> 00:04:11.760 "I see you, come over here." 95 00:04:11.760 --> 00:04:14.580 A firefly's flash is a way to send a message, 96 00:04:14.580 --> 00:04:17.339 scientists call that "a signal". 97 00:04:17.339 --> 00:04:19.499 By observing many different fireflies. 98 00:04:19.500 --> 00:04:22.529 scientists noticed a curious thing about these signals. 99 00:04:22.529 --> 00:04:27.299 Some male fireflies make a short flash every few seconds. 100 00:04:27.300 --> 00:04:29.910 Other males fly upwards as they flash, 101 00:04:29.910 --> 00:04:31.293 making soups of light. 102 00:04:32.790 --> 00:04:34.860 And remember those people we saw, 103 00:04:34.860 --> 00:04:37.860 they're watching males that match up their flashes 104 00:04:37.860 --> 00:04:40.200 so they can look like ripples of light. 105 00:04:40.200 --> 00:04:42.570 Wow, scientists now think that 106 00:04:42.570 --> 00:04:44.010 different kinds of fireflies 107 00:04:44.010 --> 00:04:45.930 have their own unique flash signals 108 00:04:45.930 --> 00:04:49.800 and there are over 2000 different kinds of fireflies. 109 00:04:49.800 --> 00:04:51.570 That's a lot of signals. 110 00:04:51.570 --> 00:04:54.487 By flashing their unique signal, males can show, 111 00:04:54.487 --> 00:04:56.879 "Hey, I'm this kind of firefly," 112 00:04:56.880 --> 00:05:00.779 and females of the same kind can recognize that signal. 113 00:05:00.779 --> 00:05:03.996 They flashback just at the right time to answer, 114 00:05:03.997 --> 00:05:07.680 "I'm the same kind of firefly too, come over." 115 00:05:07.680 --> 00:05:10.709 You can learn to recognize firefly signals too. 116 00:05:10.710 --> 00:05:12.570 There are flash charts like this 117 00:05:12.570 --> 00:05:14.940 that show the timing of different signals, 118 00:05:14.940 --> 00:05:18.300 and scientists continue to discover new flash signals 119 00:05:18.300 --> 00:05:21.930 as well as other ways that fireflies use their glow. 120 00:05:21.930 --> 00:05:23.040 They've even found 121 00:05:23.040 --> 00:05:26.310 that some kinds of fireflies are flash fakers. 122 00:05:26.310 --> 00:05:28.290 In addition to their own signals, 123 00:05:28.290 --> 00:05:29.400 they sometimes copy 124 00:05:29.400 --> 00:05:33.630 the signals of other fireflies, that's wild. 125 00:05:33.630 --> 00:05:36.510 So in summary, fireflies can make their own light 126 00:05:36.510 --> 00:05:39.150 by combining chemicals inside their body. 127 00:05:39.150 --> 00:05:41.790 Even though their flashes might seem random to us, 128 00:05:41.790 --> 00:05:42.900 they're actually signals 129 00:05:42.900 --> 00:05:45.060 that help fireflies of the same kind 130 00:05:45.060 --> 00:05:47.339 recognize each other and meet up. 131 00:05:47.339 --> 00:05:49.019 That's all for this week's question, 132 00:05:49.020 --> 00:05:51.000 thanks Siddharth for asking. 133 00:05:51.000 --> 00:05:52.379 Now for the next episode, 134 00:05:52.380 --> 00:05:54.180 we reached into our question jar 135 00:05:54.180 --> 00:05:56.339 and picked out three questions sent into us 136 00:05:56.339 --> 00:05:58.559 that we're thinking about answering next. 137 00:05:58.560 --> 00:05:59.910 When the video's done playing, 138 00:05:59.910 --> 00:06:01.860 you'll get to vote on one. 139 00:06:01.860 --> 00:06:05.707 You can choose from, "Who invented erasers?" 140 00:06:05.707 --> 00:06:08.317 "How do you fix a broken heart?" 141 00:06:08.317 --> 00:06:10.589 "Why is ocean water cold?" 142 00:06:10.589 --> 00:06:12.689 So submit your vote when the video is over, 143 00:06:12.690 --> 00:06:15.120 we wanna hear from all of you watching. 144 00:06:15.120 --> 00:06:17.370 There are mysteries all around us, 145 00:06:17.370 --> 00:06:19.503 stay curious, and see you next week.