Amphibians
Crucifix Frog
Notaden bennettii · also called crucifix frog, holy cross frog, crucifix toad
The crucifix frog is a round, yellow, almost ball-shaped frog from the black-soil plains of inland Australia, named for the pattern of coloured spots on its back that forms a rough cross. It spends most of its life sealed underground — and when something does dig it up and attack it, its skin releases a glue so effective that surgeons want to use it.
Overview
The crucifix frog lives in the cracking clay floodplains and claypans of inland New South Wales and Queensland. It is a plump, short-limbed frog 4–7 cm long, yellow to olive, with a scatter of dark-ringed red, yellow, and black spots on the back arranged roughly as a cross. It eats almost only ants and termites.
A life underground
It burrows into the soft clay and seals itself in a cocoon of shed skin, with only the nostrils clear, and can stay dormant for months or years between suitable rains. After heavy rain fills the claypans, the frogs emerge and breed explosively within a few nights, the males giving a soft owl-like call.
The glue
Threatened, the frog exudes a milky secretion that sets in seconds into a strong, stretchy, extremely sticky solid, gluing the jaws of attacking ants and deterring larger predators. Researchers have found it bonds to wet living tissue, stays elastic, is non-toxic, and is broken down by the body, and have developed it toward repairing torn cartilage such as the knee meniscus.
Status
The crucifix frog is Least Concern. It is seldom seen because of its underground life, but appears secure across a broad range of inland eastern Australia.
Crucifix Frog: common questions
Why is it called the crucifix frog?
The name comes from the pattern on its back. Against a yellow or olive ground, the frog carries a scatter of small raised spots ringed in black and coloured red, orange, or yellow, and in many individuals these are arranged so that a rough cross or crucifix shape stands out down the midline and across the shoulders. Hence crucifix frog and holy cross frog. The bright, contrasting spots are thought to be a warning display, backing up the frog's sticky, distasteful skin secretion, and the frog will arch its back and present them when disturbed.
What is the frog's glue, and is it really used in surgery?
When a crucifix frog is attacked it releases a milky fluid from glands in its skin that, on contact with air, turns within seconds into a strong, rubbery, extremely sticky solid. In the wild this immobilises biting ants and fouls the mouth of a predator. Materials scientists in Australia became interested because a fast-setting adhesive that grips wet, moving, living tissue, stays flexible, and is then safely absorbed by the body is exactly what surgeons want for repairing soft tissues that are hard to stitch. Laboratory and animal studies have used a version of the frog secretion to bond torn cartilage, and it is being developed toward clinical use, though it is not a routine treatment yet.
How does the crucifix frog survive in the desert?
It does not really live in true desert, but it does live in dry, seasonally flooded inland country where surface water is absent for long stretches. Its strategy is to go underground. Using its short, strong legs it works its way down into the soft cracking clay, and it then sheds successive layers of skin that build up into a nearly watertight cocoon around its body, with only the nostrils clear. Inside this cocoon it drops its metabolism and loses very little water, and it can remain dormant for a long time, emerging to feed and breed only when heavy rain soaks the ground and refills the claypans.
Is the crucifix frog poisonous or dangerous to handle?
It is not dangerous to people. The skin secretion is an irritant and tastes foul, which is its point, but it is not a potent toxin, and the frog has no other defences worth worrying about. Handling one leaves a sticky residue on the hands that is difficult to wash off and, according to people who have done it, has a distinctive smell, so the usual advice applies of not rubbing your eyes or mouth and washing thoroughly afterward. For the frog's sake, handling should be brief and with wet hands, since dry hands damage amphibian skin.