1Hey, it's Esther.
2What's the coolest thing you've ever seen outside after dark?
3Maybe it was fireworks or a full moon.
4These people are getting ready to watch something you can only see when it's dark.
5If you can, you might wanna pause the video now and turn the lights off to watch too.
6Check it out.
7...
8Someone named Siddharth has a question about what's making these flashing lights.
9Let's call Siddharth now.
10Hi Siddharth.
11I have a question for you, why do fireflies glow?
12Great question!
13Did you guess that those lights were fireflies,
14or you might call them lightning bugs?
15Maybe you've even seen some in person.
16When I'm camping, I've watched them in fields near my tent.
17Even though they're called fireflies and lightning bugs,
18this isn't light from fire or lightning,
19it's not from light bulbs either.
20This is light you can catch.
21Up close, you can see that this is an insect.
22Do you notice how these parts look different?
23Light can shine through them, like this.
24The light shining through is actually made inside the firefly's body.
25Different chemicals in its body combine to make light.
26Scientists have been able to create similar chemicals.
27Watch what happens when they mix two.
28...
29So each light you see here is a firefly combining chemicals in its body.
30How amazing is that?
31You may have noticed that fireflies don't stay lit up.
32Instead, they flash their lights on and off.
33But what's all this flashing about?
34I'm curious, what do you think?
35What are fireflies doing when they flash their lights?
36This is a question scientists are curious about too,
37and it's a hard one to answer.
38Fireflies don't think and act the way people do,
39and we can't really think like fireflies.
40That's why scientists start with what they can see and measure, their observations,
41to better understand what fireflies might be doing.
42When you watch a group of fireflies, their flashes can seem random,
43it's hard to keep track.
44But what if you focus on one firefly?
45You can see where it flies and when it flashes.
46Now, it's difficult to film fireflies in the dark,
47so we're gonna have to switch to a drawing.
48But what you'll see next is based on real observations of some fireflies.
49Okay, here's our firefly.
50Watch how it flashes every few seconds as it flies along.
51Our firefly keeps circling back to one area.
52And look, did you see the flash below?
53There's another firefly down on the grass.
54Our firefly keeps flashing,
55and now the other firefly has started to flash too.
56They keep flashing back and forth.
57Then, something new happens.
58Our firefly flies down and lands next to the one in the grass.
59This is something scientists have observed many times.
60A firefly flashes as it flies around,
61another flashes back.
62They flash back and forth,
63then the two meet up.
64Maybe you guessed earlier that flashing helps fireflies find each other in the dark.
65And you're right!
66That seems to be one reason why fireflies flash.
67Through their observations, scientists have also learned that the ones flashing as they fly are usually boys.
68Another word for them is males.
69The ones flashing back from the grass are usually females or girl fireflies.
70It's like the males are flashing, "Hey, check me out,"
71and the female flashes back. It's like she's answering,
72"I see you, come over here."
73A firefly's flash is a way to send a message,
74scientists call that "a signal".
75By observing many different fireflies.
76Scientists noticed a curious thing about these signals.
77Some male fireflies make a short flash every few seconds.
78Other males fly upwards as they flash, making soups of light.
79And remember those people we saw,
80they're watching males that match up their flashes so they can look like ripples of light.
81Wow!
82Scientists now think that different kinds of fireflies have their own unique flash signals
83and there are over 2000 different kinds of fireflies.
84That's a lot of signals.
85By flashing their unique signal,
86males can show, "Hey, I'm this kind of firefly,"
87and females of the same kind can recognize that signal.
88They flashback just at the right time to answer,
89"I'm the same kind of firefly too, come over."
90You can learn to recognize firefly signals too.
91There are flash charts like this that show the timing of different signals,
92and scientists continue to discover new flash signals as well as other ways that fireflies use their glow.
93They've even found that some kinds of fireflies are flash fakers.
94In addition to their own signals,
95they sometimes copy the signals of other fireflies.
96That's wild.
97So in summary, fireflies can make their own light by combining chemicals inside their body.
98Even though their flashes might seem random to us,
99they're actually signals that help fireflies of the same kind recognize each other and meet up.
100That's all for this week's question.
101Thanks Siddharth for asking.