Not sure why there isn’t a map 
But here is a location of all the coloured “Dead scarabs” 
You find in the City of the Sun God 
Collecting any 3 (Must be 1 of each colour) will grant Lore 7 “Arthropods” in The Bestiary.
You can add these to your map (Right click with your map open to add a marker)
or follow the map I have made!
Locations are as follows:
Red Scarabs: (595,300) - (820,635) - (260,900)
Black Scarabs: (295,178) - (215,1010) - (320,540)
Green Scarabs: (190, 310) - (610, 680)
Personally I find maps easier to follow than just co-ords because there is no native co-ordinates anywhere in game that is constantly visible to track your location. 
You can use LoreHound mod from CurseForge to help detect the scarabs when you are nearby.
HAPPY HUNTING!