 When they are newly hatched , frog larvae feed on the yolk of the egg . When this is exhausted some move on to feed on bacteria , algal crusts , detritus and raspings from submerged plants . Water is drawn in through their mouths , which are usually at the bottom of their heads , and passes through branchial food traps between their mouths and their gills where fine particles are trapped in mucus and filtered out . Others have specialised mouthparts consisting of a horny beak edged by several rows of labial teeth . They scrape and bite food of many kinds as well as stirring up the bottom sediment , filtering out larger particles with the papillae around their mouths . Some , such as the spadefoot toads , have strong biting jaws and are carnivorous or even cannibalistic . 
