Naturespeak A naturalist's view of the world

November 5, 2009

Quality Tadpole Time

Filed under: Uncategorized — wykes @ 10:00 pm

November might seem an odd month to turn one’s attention to the subject of tadpoles. Indeed, most of the tadpoles out there have already converted over to adulthood and are now preparing to over-winter as four legged folk. Bullfrogs (and some Green Frogs) are the exceptions to this rule. They overwinter at least once (often twice or more) as a tadpole before moving on up into the big leagues. November, therefore, is a time when these big babies are still very active under the cold gray water.

I can’t really tell you why I chose to spend some quality Bullfrog tadpole time this week – call it guilt, I guess. The local marsh is chock full of  wiggling bullfroglets who make their presence known by breaking the surface for an occasional  gulp of air (you could say they are breaking wind). I momentarily stop to watch them but generally continue on. There’s only so much you can get out of a swarming mass of tadpoles sequentially breaking wind.  I also have two of these critters sitting in my aquarium and they spend a lot of time staring blankly through the glass. I’ve walked by them countless times without giving them so much as a glance. When I do glance over, I find them doing absolutely nothing for long periods of time- aquarium tadpoles apparently don’t find it necessary to break wind. They are, in fact, hard to see against a weedy background thanks to some superb camouflaging (see here).

Recently, I realized that a glance wasn’t enough.  Bullfroglets don’t give up anything at a glance – they require a prolonged visual assessment. Up close and personal, they are really exciting…o.k., not exciting…let’s just say fascinating.  They are fully developed creatures in their own right and much more than mere transitional forms. They are neither fully fish nor frog.

We can chalk that mindless fish look down to the fact that they have no eyelids. Adult frogs have the ability to close their eyes, but the young-uns are condemned to a life of blank unfocused staring. This look is accentuated by the fact that they hold their mouths open all the time. They breath using gills – two sets of three contained within a pouch behind the mouth- and, like fish, they take in water through the mouth and tiny nostrils and pass it through internal slits and over the gills. Unlike fish, however, these gill chambers are sealed and all the water is expelled through a single breathing pore located on the left side of the head (see above view).  This breathing pore, which appears as a spout, is hard to see unless it is in use. The adults are red-blooded lung-possessing air breathers

Bullfrog tadpoles also have lateral line spots just like fish. These special sensory organs are equipped tiny “hairs” (frog fur is very fine) which detect motion and changes in water pressure. The adults have no such thing because they rely on excellent eyesight and sound detection to avoid predators. Tadpoles can’t see or hear very well…I said TADPOLES CAN’T HEAR VERY WELL…they have no middle ear and apparently hear what they need through their skin (and what remarkable skin it is – look here at a detail). There is probably little need for a sophisticated ear to listen to all their aquatic buddies blowing bubbles in the tub.

Speaking of organs, perhaps the most remarkable organ is the mouth (see detail above and here). Here we have a beast that has a tiny mouth equipped with a horny beak (you know, like that giant squid that tried to eat Kirk Douglas in 20,000 leagues Under the Sea), fleshy lips (like Sydney Greenstreet in the The Maltese Falcon), and multiple rows of teeth on its lips (like…absolutely nothing else on the planet!). Yes, the Bullfrog tadpole has three rows of comb-like teeth on the lower lip and a few rows on the upper lip as well. Tadpoles are algae eaters. Every time the tadpole takes a bite with that beak those rasping lip teeth rake the surface like an industrial sander. There are even dozens of rubbery “lip fingers” lining the outer fringe of the mouth to prevent food particles from floating away.

There are many other Bullfrog tadpoles high points to cover, but after mentioning those incredible lips I feel that there is no real need to continue.  QTT has it’s limits.


  1. The whole tadpole-to-frog transformation is so amazing, it always remains a wonder! I know Am. toads call/breed way later in the season than other frogs, but didn’t realize they can overwinter as tadpoles more than once. Do they have a longer transformation period? I saw tons of tiny (and then bigger) Am. toads in summer (they breed in a vernal pool behind my house), but I didn’t realize there could be a second set of babies. ??

    Comment by Monica the Garden Faerie — November 6, 2009 @ 12:58 pm

  2. Who knew tadpoles had so many fascinating secrets!?! The breathing spout on the side of the head is pretty cool. Wonderful close-up shots, too. I think QTT is something more of us should do. Hm…where can I find some tadpoles…

    Comment by Ellen — November 6, 2009 @ 2:27 pm

  3. Actually tadpoles have extraordinarily good hearing and certainly have middle ears. What they lack are external tympani (eardrums). They hear using a mechanism similar to some fish where the sounds directly stimulate the oval window and pass this on to hair cells in their multiple inner ear organs. When they grow their hind legs and are about to have their forelegs emerge, they grow a second auditory pathway which transmits vibrations to the new forelimbs. Ranids don’t growe an external eardrum until they complete metamorphosis as that system is meant to pick up sounds mainly from air.

    Comment by Seth Horowitz — January 18, 2010 @ 12:25 pm

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