Is it a male or a female? It is simpler to differentiate between the two than you may think.
As caterpillars, we cannot tell the difference between male and female Monarchs. Beyond that, we can and you will soon be able to tell too. You can determine the sex of both chrysalises and adults.
Adults are simplest. Males have dots on their hindwings.
Female adult Monarch butterflies are slightly darker and have wider black lines on their wings.
Although the male’s black dot isn’t as visible from the outside of the wing, the area where it is located can be seen when its wings are closed.
As chrysalises, it takes good eyesight or taking a photo and enlarging the photo. Just below and between the lowest two black bumps/dots (holdfast tubercles) on the chrysalis, there will be either a short or long indentation.
The male’s shorter line is touching the abdominal segment line that touches the holdfast tubercles. The female’s longer line touches the abdominal segment below the line that touches the holdfast tubercles.
(Click on any photo to see a larger image.)