Tuesday, April 7, 2009

Tadpoles Compared

Here's a California toad guarding his hole from the foreclosure agents. You can tell he is a toad by the yellowish line down his back. And the warts. But how do you tell a toad tadpole? They're black commas.

Let's update the progress of the toad eggs. We originally mistook them as tangled shoestrings in the Newt Pond on March 18th. California toad eggs are black dots laid inside long, double-walled, clear jelly tubes. On March 22, we noticed the tubes had started to break apart even though the eggs were still roundish and the embryos were not developed. Toad tadpoles hatch out in 5 or 6 days by busting through the jelly tube.

<--- busted toad tubes by David Tharp ---

I am not sure why these tubes were already broken apart. My guesses are: the Newt Pond is high on a ridge, and sometimes the wind creates a fetch that agitates the shallow water and may have broken up the tubes prematurely. Curiously, we saw many tiny, white mite-like critters clustered on the jelly tubes and maybe they were breaking them up. Or maybe the hatching is spread apart by several days and some tadpoles busted out early, loosening their brethren eggs. Good thing the toads hatch out in just a few days, otherwise, I would probably come up with more theories.

<--- 'mites' on toad tubes by David Tharp ---

In any event, the hatching seemed successfully, as by April 5th, thousands of toad tadpoles were massing along the edges of the pond. The toad tadpoles start out about 6 mm long and are dark black, so black you can't make out their features.

Compare this to the Pacific treefrog tadpoles that hatch in 6 days, quickly grow to 1 cm, develop enormous tummies and are camouflaged with dark olive backs marked by black dots and a coppery underside.

<--- treefrog tadpole on left, toad tadpole on right ---

I am not sure why the toad tadpoles are so dark and obvious and the treefrog tadpoles have cryptic coloring. I carefully watched adult newts nosing about the pond vegetation in a hunting pattern and they did not snap at the black commas as they wiggled by. Adult toads have toxic, foul-tasting substances (Pickwell) in their "warts" (why dogs usually spit out toads), but I don't know if the tadpoles are so equipped. Pickwell notes that predacious water insects capture and suck the fluids from frog and toad tadpoles.

Meanwhile, the newt eggs have been developing into twitching knife-like larvae and carving out of their individual eggs and then the outer casing. A number of newt egg clusters were washed up on shore on the windy day I last visited the Newt Pond. As I tossed them back into the pond, I noticed several newtlets pop out of the floating cluster and swim away. I cheerfully shouted, "I birthed them!" and the coyote hunting rodents in the nearby meadow looked my way.

<--- newt larvae about to bust out ---

Toad and frog tadpoles are herbivores and spend their days scraping up algae and decaying matter from rocks and the pond bottom with sucking mouths and tiny teeth. Newts are carnivorous all their life, so their larvae are devouring small pond critters. I rarely see newtlets in the ponds; as carnivores, maybe they lurk in the shadows.

The toad tadpoles will metamorphize in about 8 weeks from egg laying or mid-May. Will the water in the Newt Pond last that long? It rained today, so maybe. They hop out of the pond as tiny toads 6 mm from snout to tail end, and sometimes they still have a bit of tadpole tail they carry around for awhile. The treefrog tadpoles take about 12 weeks to metamophize, so that would be mid-June. Hmm, not sure if the Newt Pond is going to last that long, but treefrog eggs in the deeper Plum and Mallard Ponds will certainly have enough water to get to hopping stage.

I rarely see tadpoles of the California red-legged frog. They are larger (up to 7.5 cm long), dark brown or yellowish above, shiny pink below with white spots in a line along each side (Stebbins). From above, their eyes are closer to the centerline of the head and not along the outer edges like the treefrog. Both the red-legged frog tadpoles and the newtlets can spend over a year before they metamorphize, so they need longer-lasting ponds.

Thanks to my pond companions who provided some of these great photos and co-speculate on the mysteries of shoestrings and busted jellies. We are going to have a toad party in May if the Newt Pond lasts that long.

<---can you find the hidden treefrog tadpole?---

See also:
California toad, Bufo boreas halophilus
Pacific treefrog, Pseudacris regilla
Coast range newt, Taricha torosa torosa
California red-legged frog, Rana draytonii

Gayle Pickwell, Amphibians & Reptiles of the Pacific States, Dover Publications, 1972.
Robert C. Stebbins, Western Reptiles and Amphibians, 2003.

1 comment:

  1. I just watched a PBS special on frogs called 'the thin green line'. It was so upsetting. Loss of habitat, pesticides and the fungus are killing them off and entire areas of quiet...But I guess you know that already....Great post, I learned a lot..Michelle


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