Honey I don't think they're monarch butterflies, they look more like viceroy butterflies to me.
But they look just like the monarch butterflies that we learned about at school.
The scientific term is stabilizing selection. Basically what happens is that the viceroy butterflies change their appearance to mimic the monarch butterfly. Doing that confuses predictors into thinking it's poisonous, just like the monarch.
Um okay but how could you tell the difference?
I could tell because they're smaller and viceroy butterflies have a black line across their hind wings. The process of mimicking the monarch butterfly is called stabilizing selection. Over time, they evolved their wings so that they are similar but the caterpillar of a viceroy and monarch butterfly have many differences.
Okay that was a lot of unnecessary information mom. I'm going to play some video games now.