I will add a new reason. They are pleasant to study. They are small, hard and easy to manipulate and keep dry. A big collection fits in any room and they have

I will add a new reason. They are pleasant to study. They are small, hard and easy to manipulate and keep dry. A big collection fits in any room and they have an entertaining endless diversity of forms and colours, so primates like to collect them. Don't believe me? How many roundworm or fly species do we know? How many we don't know still?