How do you tell if a caterpillar is a boy or girl?

It is very difficult to tell without disecting them. You can often tell on moths and butterflies by their markings. Hope I helped. 

Well you usully tell by colourings but that is not the case with cateriplars you can not tell by markings like you can with moths. you can sometimes tell by the hair but this only works with some species. sadly you cannot tell that clearly with caterpilars all you can do is weight for them to turn into moths or butterflies hope i helped

True as the lakes are a marine body. also there's no difference in lake and ocean except for the size.