I don't know how it came to be called as such but to Ilonggos, these are tiny dried shrimps. Methinks its actually shrimp fry or baby shrimps.
Mostly used as garnishing over kalo-kalo (fried rice); however it can be of many uses depending on the imagination of the cook. One of the more common ways of using kalkag is making a torta of out of it. Just mix it with some seasoning, egg and flour then fry.
Or just sprinkle them over laswa or any vegetable dish, as garnishing and mild flavouring as well. Most of the time though, I just heat them over a pan (without oil) or just mixrowave, for around half a minute and mix it with rice.