Wednesday, 21 November 2012

A Sad Fate for a Harmless Snake

About 80 years ago a group ill-informed, but well-intentioned, folk introduced the Cane Toad, Bufo marinus, to Oceania, including Australia. Their vested interest- protection of the sugarcane industry.
Bufo marinus, the Cane Toad or Marine Toad

The rationale behind this introduction was that the voracious appetites of the toads would be a great advantage in controlling the cane beetles (Scarabaeidae) that infest the cane, the larvae of which feed on the roots of the plants.

The knowledge of the biology of the toads and the beetles was severely wanting. Toads live on the surface of the ground and would not come into contact with the grubs of the beetles. Well, you could argue that they would feed on the adults. Yes and no. Adult cane beetles are large, 30 mm or more in length, and only an adult toad could cope with them. And, the most important aspect of all this is that when the beetles emerge from the soil they fly away from the site and only by chance would come into contact with the toads.

Two other aspects of this untimely introduction have to do with the biology of the toads. They are voracious all right. They eat just about anything they can get down their gullets. In many places they have literally eliminated the ground fauna of nocturnal insects. Not only insect, they will consume anything they can get down. Other frogs and toads and sleeping lizards (mostly small skins) are consumed.

But they other aspect of their biology has to do with their toxic nature.
Last night I had the opportunity to observe the toxic nature of these toads. A Slaty-grey Snake, Stegonotus cucculatus (Dumeril, Bibron, Dumeril) (Colubridae) was found dead in our driveway with a cane toad in the grasp of its mouth. 

The Slaty-grey Snake feeds on a variety of vertebrates but there are many incidents of cane toads causing their deaths.



This snake was stopped in its tracks by puncturing the parotid glands of the toad. These glands secrete a  powerful alkaloid called bufotoxin which acts as a neurotoxin. It seems to work quickly.

The problem with these toads in the 80 years they have been in Australia is that the majority of Australian species have no way to deal with bufotoxin. There are no native Bufo in Australia and our fauna have had no evolutionary experience in coping with it. As a result may species have been affected by the toads. Quolls seem to be especially vulnerable with virtually every individual that attempts to eat a cane toad poisoned. This is a scenario not anticipated by the group that introduced the Cane to to Oceania--I hope.

I have left the snake in place in the driveway to see if it is avoided by the cadre of Brush Turkeys that will make their way to the front door later in the morning. Heavy truck traffic on Black Mountain Road has caused the Cassowaries to avoid crossing so they will not come into contact with the toxic snake.

And that begs the question: Can cassowaries cope with cane toads? I wonder. They eat some very toxic seeds and they do eat vertebrates if they find them.

I will keep you posted.

3 comments:

Camera Trap Codger said...

Great observation, Dave. Your eyes are open, and you're a "curious naturalist" (which is good). Enjoy the turkeys, and lets hope they didn't down any cane toads before the last rites.

Mr. Smiley said...

Yes, I guess my eyes are open. That observation was made at 1.30 am!
D

randomtruth said...

Really interesting Dave. I knew of cane toads and their poisons, etc., but had no idea they could be so fast acting if the gland was punctured like that. Wild.