Bullfrogs take 2 years to mature from egg to adult. The tadpoles will be 2"-3" long and the body will be about 1/2"-3/4" across. Bullfrog tadpoles are more of a brown color, if you're seeing a lot of black tadpoles, those are most likely toad tadpoles.
The small ones I have by the thousands are very dark--probably toads. But the larger ones I think are probably bullfrogs.
Do you have adult bullfrogs in the pond or close by now?
I think I heard one a few nights ago.
