Why Do Mantis Eyes Turn Black At Night?

[twentyeggs]

Hello, I have scoured Google and I cannot find the answer. All I get are responses like, their eyes don’t turn black, they turn dark when they are dehydrated, and jokes about night vision. 
 

I don’t know about all Mantis species but I have been keeping the ones in North America my entire life. They absolutely without fail turn dark to pitch black when they are without light for more than a few hours. 
 

So the question is why, and how do they do this? 

 

[MantisMart]

Those are what we call "night eyes" or as I like to call them "puppy dog eyes".

It happens at night, don't ask me why, all I know is that there eyes change colors depending on the time of day.

Night eyes probably help them see in the dark I dunno.

Mantids are pretty wonky, they keep ya on ur toes.

 

[twentyeggs]

Yeah, I find it interesting this is not a commonly found answer. These are extremely common insects and usually a favorite/at least interesting species among entomologists. 
 
Human eyes look black as the pupil grows to let in more light. I’m looking for a reason like that. There has to be a reason.

 

[Mantid-Tim]

They darken at night as a part of a process that helps them see better at night. It does let more light in I believe. 

 

[nzxmUyZNKEBoqN3e]

As said above. Perhaps I'm wrong, but it could be to do with increasing absorption of light; just as our pupils get bigger to absorb more light and therefore see better, a mantids eyes likely darken to achieve the same thing. Given a mantid's visual acuity is their primary mode of offence and defence, it seems likely that mantids with the ability to see better at night would do better in evolutionary terms.