While checking traps recently, I noticed a lot of activity in the water in several recently flooded fields. A quick glance into the water might make you believe that tadpole shrimp is present in large numbers, or even perhaps that a treatment did not work. Make sure you look closely and don't confuse clam shrimp with small tadpole shrimp.
Clam shrimp
Clam shrimp are small crustaceans that look like a miniature clam; they are about a tenth of an inch and swim in the water slowly. Clam shrimp don't have the "tail" that tadpole shrimp have at the end of their shell. Most freshwater clam shrimp feed on algae and organic detritus. I am not sure what the ones in rice fields feed on, but they do not injure the rice. In the past, I have noticed that these clam shrimp come back after a tadpole shrimp treatment very quickly.
Clam shrimp close up
Large congregation of clam shrimp around decomposing rice roots
Tadpole shrimp are more problematic during seed germination. Once the seedlings have a well anchored root and the spike is green, tadpole shimp are less likely to injure them.