The fossil plants found in the Eocene Florissant Formation and Green River Formation are preserved with a level of detail that allows one to closely examine traces of insect feeding damage. Levels (amounts) and patterns (abundance of various types) of fossilized insect feeding damage from Florissant and the middle Eocene Green River Formation were compared. This allowed for a detailed examination of feeding damage and provided an opportunity to examine long-term patterns of change in insect herbivory during a period of climate fluctuation. Samples including 624 fossil leaves from Florissant and 584 fossil leaves from the Green River Formation were examined to document overall damage levels, the presence/absence of specific feeding guilds (i.e., hole-feeding, skeletonization, leaf-mining), and host-specific damage types.

Florissant insects show host specificity in their feeding preferences as evidenced through the distribution of feeding damage on plants and through the presence of identifiable host-specific interactions. Some of these interactions appear to be long lasting as they are also apparent on the same, or closely related, leaf species found in the Green River Formation. Insect damage levels declined from the middle to late Eocene. This decline is correlated with a cooling event during this time interval and is in concurrence with the findings of other authors who have examined fossilized herbivory and climate change patterns. There is also an increase in the abundance of galls during this same interval, which also may be related to climate change.