The crayfishes Procambarus clarkii and Fallicambarus fodiens are approximately equally abundant in Texas, yet currently there are fifty times more clarkii observations (257 vs. 5).

https://www.inaturalist.org/observations?place_id=18&quality_grade=any&taxon_id=51221

https://www.inaturalist.org/observations?place_id=18&quality_grade=any&taxon_id=100848

The difference is that clarkii inhabits areas such as ponds, lakes and streams where they are likely to be seen by humans, whereas fodiens occurs more in ditches and field, and spends most of their time hidden in burrows.