Thanks for the great info! How can you tell if a springtail is male or female? Also, how do they change between feeding and reproductive instars?

to tell if a specimen is male or female. Collembola do not have external reproductive organs. However, the shape of the sexual opening, ventrally on the 5th abdominal segment, is different. In females, the sexual opening is a transverse slit having 2 kind of lips, an anterior and a posterior lip, each with a row of setae. In males, the sexual opening has the shape of a keyhole directed longitudinally and surrounded by several circles of setae. In many Symphypleona the male sexual opening is on a raised papilla which can be seen in 'low level' lateral aspect pictures. Some Collembola display sexual dimorphism but these are exceptions.

Changing from feeding to reproductive instar happens simply by moulting. Contrary to Insecta, Collembola keep on moulting in adult phase. After each moult an adult specimen changes functionally. In feeding instar phase the specimen will only feed. In reproductive instar phase (after moulting) the specimen does not feed but thinks only about having sex ;-). After the next moult it is back in feeding phase where it lost all interest in sex. This cycle goes on untill death. We could say that Collembola regain virginity every 2 moults.