Early Instar sexing for Praying Mantis
Definitions.
Segment: repeating units that make up the body of an arthropod, not always as clearly defined as you'd think (e.g. the thorax is made up of 3 segments but you have to look real close to see the lines).
Tergite: the hard plate on the top, or dorsal side, of a segment.
Sternite: the hard plate on the bottom, or ventral side, of a segment (think like, your sternum is on the front of your body).
Segment/sternite/etc. number: this isn't official terminology but if I say segment 1 on the abdomen I mean the one closest to the front end of the mantis, not the back end.
All mantises, barring some terrible accident, actually have 11 abdominal segments.
So why do we say females have 6 segments and males have 8? Well, first off, females have 6 visible sternites, but if you look at the top of the abdomen you can see there are still like 8 or 9 visible tergites, because it's the underside of these segments that gets modified into the genital structures as they mature.
In males you see 8 abdominal sternites, because segment 9 is modified into the genital structure, and held internally until mature and needed.
In females, you see 6 abdominal sternites, and segments 7-9 are tucked away under/inside that plate and form the internal genital structures.
Segments 10-11 are highly reduced and always internal in both sexes so I'm ignoring them.
This is why you can't sex L1 nymphs, because they all have the same number of external sternites as nothing has started to differentiate yet. For most species, by I2-I3 females have only 6 visible sternites and sexing is easy but this is not always the case. E.g. Acanthops sp. which, at I3, still have 8 visible sternites on both males and females.
In these species though the differences have still usually begun to develop often.
Many of you will have noticed that an adult female mantis has a final segment that looks like a jug spout, while males look like a simple flap, and the start of these changes can be seen at earlier instars by looking at the shape of the 6th sternite. In female orchid nymphs and Acanthops there's a distinct notch M shape.
