Sexing Question

I've heard that you can't tell the difference between a male and female common til their about a foot long. How do you tell the difference? My 3, except for the sizes, all look alike. But then again I don't know what to look for.

High Eaglehorsesmom, common what?,pleco I'm assuming.
L023- Pterygoplichthys Pardalis (Common pleco): You are right about the size thing , they need to quite
large to be able to sex them , but then you need to get a look at their genitalia which is usually only visible
after spawning. If you ever get them to spawn in a tank give yourself a pat on the back, as this is hard to
achieve, if you have a dam or large mud pond you would have a better chance as they spawn in tunnels
that they dig in to the mud.
Cheers J

the males get heaps bigger then the female i have had 2 for years the male is around 40cm the female 30cm and you need mud or clay for them to burrow in for them to spawn