what's this bug
I have some bugs eating plants in my pond. They are 1/2 to 3/4 inches in length. They seem to prefer marsh marigold and ranunculus but are also on cattails. They are skeletonizing the plants they are on. I don't want to use pesticides since these plants are in my pond with koi. I have been hand picking. Would also like to know if they are going to invade my terrestrial garden. They do drown if put in a cup of water so I don't think they are particularly water pests.
Jefferson County Colorado
It is some type of blister beetle in the genus Epicauta. There are several species in CO that are gray like this.
The adults of some blister beetles feed on flowers of various plants, and sometimes the leaves. (Others just feed on pollen) However, serious outbreaks are extremely rare and usually short-lived and highly localized. Normally they do a modest amount of feeding, often overlooked it is so minor, and then disperse on their own. And, although I can not say that you do not have plants elsewhere where they may do a bit of chewing, the damage is minor and not worthy of a response beyond some hand picking.
Numbers of these insects are cyclical. Since the young stage of this beetle developed by feeding on the eggs of grasshoppers, the numbers of blister beetles usually track with grasshoppers (blister beetles follow grasshoppers).