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33 Facts About the Strange Crucifix Frog or Holy Cross Toad

Linda Crampton is a writer and teacher with an honors degree in biology. She loves to study nature and write about living things.

This is a male crucifix frog. Many animals in the species have a bright yellow or lime green background to the cross pattern on their back.

This is a male crucifix frog. Many animals in the species have a bright yellow or lime green background to the cross pattern on their back.

An Odd Amphibian From Australia

The crucifix frog or holy cross toad is an Australian amphibian with an unusual appearance and some intriguing behaviour. The scientific name of the animal is Notaden bennettii. It was given its common name due to the appearance of a cross on its back. This cross is most obvious in the animals that have a light background colour, like the one in the video below. The frog spends much of its life underground and produces a sticky secretion that may be medically useful for humans.

The amphibian is also known as the crucifix toad, the holy cross frog, and the Catholic frog. It has both frog and toad characteristics. The scientific publications that I've read refer to the animal as a "frog", so I'll follow their example. Whatever it's called, it's an interesting animal to investigate. In this article, I describe thirty-three facts about the amphibian that you may not know.

The crucifix frog belongs to the class Amphibia, the family Myobatrachidae (Australian ground frogs), and the subfamily Limnodynastidae. Some researchers feel that the Limnodynastidae category should be classified as a family, not a subfamily.

Distribution, Habitat, and Appearance

1. The crucifix frog lives in parts of Queensland and New South Wales that are dry for most of the year.

2. It's found in semi-arid grasslands and black soil plains that are rich in clay. The ground forms cracks as it dries out and softens during the rainy season.

3. The frog has a round body, short legs, and relatively large eyes. The short limbs reduce the surface area for water loss.

4. The body of the adult is between 1.8 and 2.6 inches in length.

5. Many members of the species have a yellow or light green skin covered with black and red bumps that form a cross shape. The upper part of the cross typically has two bars instead of one.

6. In some animals the background colour is olive green or brown, but the red and black cross is still present.

7. The frog is said to exhibit aposematism, which is the use of bright colours to warn predators that they shouldn't attack.

8. In the case of the crucifix frog, it's not clear why the warning is given. The frog produces a sticky secretion. The secretion may block the predator's mouth and breathing passages when it enters them, it may taste bad to predators, or the frog may be poisonous. As described below, the secretion has properties that make the first explanation seem probable. This doesn't eliminate the possibility that one or both of the other explanations may be correct as well.

9. The Australian Museum recommends that anyone who has handled the frog avoids touching their eyes before washing their hands. The museum says that some scientists who haven't done this have reported "painful stinging and headaches".

States and territories of Australia; the crucifix frog is found in Queensland and New South Wales in eastern Australia

States and territories of Australia; the crucifix frog is found in Queensland and New South Wales in eastern Australia

Life Underground

10. The frog is classified as a fossorial animal (one that spends most of its life underground).

11. The amphibian buries itself at least one metre deep in the ground. According to some reports, it sometimes hides at a depth of three metres.

12. While it's buried, the frog is encased in a waterproof cocoon (except for its nostrils). The cocoon consists of multiple layers of skin. The cocoon and the depth at which frog is buried prevent the animal from drying out.

13. The animal's body almost certainly has physiological adaptations that enable it to survive. In other burrowing frogs that have been studied, the breathing, heart, and metabolic rates of the animals decrease dramatically during estivation. (Estivation or aestivation is dormancy during hot and dry weather.) Chemical changes within the cells of the animal often occur during estivation as well.

14. The protection from dehydration is apparently very successful, since the crucifix frog survives for almost a year until the next rainy reason. It can stay underground for more than a year if the rain doesn't make the ground sufficiently soft during a season.

15. The percentage of frogs that survive the underground period is unknown, but the population of crucifix frogs isn't believed to be in any trouble. The IUCN (International Union for Conservation of Nature) gives the caution shown below, however.

16. The IUCN classifies the animal in its "Least Concern" category. The last population assessment was done in 2004. The animal's status badly needs to be updated.

Habitat loss/degradation associated with intensive agro-industry farming is a threat to the species in parts of its range.

— International Union for Conservation of Nature

This is a small crucifix frog. The Australian 20c coin in the photo has a diameter of 28.52 mm.

This is a small crucifix frog. The Australian 20c coin in the photo has a diameter of 28.52 mm.

Life Above Ground

17. When the ground has absorbed enough water from rain to become soft, the frog sheds and eats its cocoon, emerges from its hiding place, and searches for a temporary pool of water that has formed in a depression.

18. Some insects take advantage of the temporary pools that form and reproduce there. The frog feeds on the insects and larvae in and around the pools, especially ants and termites. It also eats other small invertebrates that it discovers. The first video in the article shows the frog catching insects.

19. "Pedal luring" has been observed in captive animals when they are fed live crickets. The frogs wiggle their toes to attract the insects, as shown in the video below. This behaviour has also been observed in some other species of amphibians.

20. The frog completes its life cycle rapidly before the land dries out again. The amphibian is active for six to eight weeks. It then returns to its dormancy underground.

On their back foot they have an extra, little hard shovel-y bit that they use to dig backwards into the ground once it starts to dry out again.

— Jodi Rowley, Australian Geographic (in reference to burrowing frogs)

Reproduction

21. To attract a female, a male floats on the surface of a pool with his body and legs spread out.

22. He then emits a call that is described as a "hooo" sound. It's said to resemble an owl's call.

23. A female is attracted by the male's call and releases her eggs into the pool. The male fertilizes them with his sperm.

24. The tadpoles that develop from the fertilized eggs grow rapidly and then metamorphose into adult frogs.

25. After eating as much food as they can, the new frogs go underground as the environment starts to dry out.

The video below shows a crucifix or holy cross frog at the start and a burrowing frog with the scientific name Cyclorana novaehollandiae afterwards. The latter species is found in Queensland and New South Wales and is shown in the frame below.

Frog Glue: A Potentially Useful Adhesive

26. When the crucifix frog is disturbed by humans or predators, it releases a sticky substance known as frog glue from its skin.

27. The glue may have two functions. It traps insects, which serve as food. When the frog sheds its skin (as the amphibian does periodically), it eats the glue and the trapped insects. The secretion may also repel predators.

28. Researchers have found that the secretion quickly forms a "tacky elastic hydrogel" that is rich in protein. The hydrogel is pressure sensitive and is sticky even when wet.

29. The researchers have discovered that the glue repairs meniscus tears in sheep more strongly than current protein-based adhesives used in medicine.

30. They've also found that tendon-attachment tear repairs in animals are approximately doubled in strength when the frog glue is used compared to conventional treatments.

31. Some researchers have found that the secretion contains "possibly toxic" components as well as potentially useful ones. Most sources say that the glue is non-toxic, however. The conflicting claims need to be resolved.

32. The glue may be irritating to mammals even if it's non-toxic. Scientists injected small pellets of the glue under the skin of mice. The pellets were gradually absorbed by the bodies of the mice, apparently harmlessly. The injection sites showed initial skin necrosis (cell death), but the mouse skin quickly repaired itself.

33. It's unlikely that frog farms containing animals producing the skin secretion will be established. Scientists may be able to create a similar and safe medical adhesive for humans by studying the frog product, however.

Burrowing frogs are very under-recognised by the public and they’re also incredibly poorly known by biologists because they’re so hard to study.

— Jodi Rowley, Australian Geographic

A Somewhat Mysterious Animal

Not as much is known about the crucifix frog as might be expected, perhaps because it spends so little time above the ground. Most people rarely see the animal, even when the amphibians live near them. They are curious creatures that may have much to teach us.

The role of the sticky skin secretion in the amphibian's life and the composition and properties of the secretion need to be further studied. It would be wonderful if improved medical adhesives could be created based on the study of the frog glue. The amphibian is interesting in its own right and because of its potential value to us.

References

  • Crucifix frog information from the Australian Museum
  • Facts about the frog from the Australian Geographic website
  • Information about the glue from the frog from a transcript of a TV show produced by ABC Catalyst (An Australian Broadcasting Corporation site)
  • An adhesive secreted by Notaden bennettii (Abstract) from Springer Publishing
  • Biocompatibility of the adhesive (Abstract) from the Wiley Online Library
  • Notaden bennettii entry from the IUCN
  • Information about burrowing frogs from Australian Geographic

© 2019 Linda Crampton

Comments

Linda Crampton (author) from British Columbia, Canada on February 12, 2020:

Hi, Denise, Yes, there is a lot left to study. Nature is fascinating!

Denise McGill from Fresno CA on February 12, 2020:

I'm not really into amphibians but these are interesting creatures. It seems amazing to me in the day and age that there are any creatures left we haven't studied extensively and don't know everything about them. There is so much left to study and do, isn't there?

Blessings,

Denise

Linda Crampton (author) from British Columbia, Canada on July 29, 2019:

Thank you very much, Devika. I appreciate your visit and comment. It's certainly an unusual frog!

Linda Crampton (author) from British Columbia, Canada on July 29, 2019:

That's an interesting thought. Thank you for the comment and for sharing your idea, Sherry.

Devika Primić from Dubrovnik, Croatia on July 29, 2019:

Wow! An unusual look about this frog. I am amazed of the information you gathered here. A well-researched and interesting facts about the

Crucifix Frog and I had no idea of its existence.

Sherry Haynes on July 29, 2019:

That was a fascinating account on Crucifix frog. I believe I have seen the frog before. But never knew how different it was from the other frogs. I was wondering if the name "crucifix " was given to the frog after discovering that it releases glue like substance. Just a random thought.

Linda Crampton (author) from British Columbia, Canada on May 22, 2019:

Hi, John. The animal's lifestyle is interesting. It seems strange to be active for such a short time each year, but the system apparently works well for the frog.

John Hansen from Queensland Australia on May 22, 2019:

I found this very interesting Lind. I had heard of the crucifix frog/toad but have never seen one even though I live in Queensland. But we probably don't have the black soil/clay mix needed that cracks during the dry months. Although, as you say, many people that live in the vicinity of these frogs rarely see them as they spend most of the time underground.

Linda Crampton (author) from British Columbia, Canada on May 16, 2019:

Hi, Dora. I like your explanation for why the Catholic frog is a good name! I appreciate your visit and comment.

Dora Weithers from The Caribbean on May 16, 2019:

The Catholic Frog is the name I prefer (I'm smiling). It gives the creature much respect which it deserves despite the mystery surrounding its habits. Hoping that the glue would prove useful in even more ways than scientists imagine. You always present some mind-boggling facts. Thanks!

Linda Crampton (author) from British Columbia, Canada on May 16, 2019:

Thanks for the comment, Nithya. The frog is an interesting little animal

Nithya Venkat from Dubai on May 16, 2019:

Interesting and informative article about the crucifix frog. This is the first time am reading about this frog and it is interesting to learn about their characteristics.

Linda Crampton (author) from British Columbia, Canada on May 15, 2019:

Hi, Louise. I think it's an attractive frog, too. It's an unusual amphibian. Thanks for the visit.

Louise Powles from Norfolk, England on May 15, 2019:

I've never seen this kind of frog before, but he is so cute.

Linda Crampton (author) from British Columbia, Canada on May 12, 2019:

Hi, Flourish. I assume that some animals are disturbed, but most are well protected. They bury themselves deep underground in areas that are dry for much of the year and (as far as I know) aren't likely to be deeply excavated.

FlourishAnyway from USA on May 12, 2019:

This little guy looks like he had too much to eat at the all you can eat buffet. I just wonder how scientists go from “that’s a cool animal” to “lets see if we can use it for medical adhesives.” I think about people digging holes and not knowing these frogs are underground. I wonder if they move somehow or just get “disturbed” by shovels?

Linda Crampton (author) from British Columbia, Canada on May 12, 2019:

Escaping from the world for a while sounds like an excellent idea! I hope you have a good Sunday and a great week, Manatita.

manatita44 from london on May 12, 2019:

What I need to be is a 'fossorial' animal. So I can escape this maddened cage for a good long while. Lol. I'll wait for the rain and trap whoever comes with my glue.

What an interesting specie! Happy Mothering Sunday.

Linda Crampton (author) from British Columbia, Canada on May 12, 2019:

Thank you very much for the comment, Maren.

Maren Elizabeth Morgan from Pennsylvania on May 12, 2019:

Great info!

Linda Crampton (author) from British Columbia, Canada on May 11, 2019:

Hi, Eman. I think that amphibians are interesting, too. I enjoy observing them and exploring their characteristics.

Eman Abdallah Kamel from Egypt on May 11, 2019:

The world of amphibians is full of interesting facts. This is the first time I read about this Australian frog.

Linda Crampton (author) from British Columbia, Canada on May 11, 2019:

I love your description of the frog, Heidi! Thanks for the kind comment. I hope you have a great weekend as well.

Heidi Thorne from Chicago Area on May 11, 2019:

It kind of looks like the shape of a hot cross bun, too. :)

I always find it fascinating to hear how these animals you feature have so much they can offer the fields of science and medicine.

Thanks, as always, for sharing your vast biological knowledge! Happy Weekend!

Linda Crampton (author) from British Columbia, Canada on May 11, 2019:

Thanks, Bill. I always appreciate your visits and comments.

Bill Holland from Olympia, WA on May 11, 2019:

Haven't heard from you lately, Linda, but the wait was worth it. I can always count on you to deliver some fascinating facts.

Linda Crampton (author) from British Columbia, Canada on May 11, 2019:

Nature never ceases to amaze me, too, Bill. Thanks for the visit and the comment.

Linda Crampton (author) from British Columbia, Canada on May 11, 2019:

Hi, Pamela. I think it's impressive that the animal can live so long underground. I appreciate your visit.

Bill De Giulio from Massachusetts on May 11, 2019:

Hi Linda. What an interesting frog. Once again you have introduced me to a creature that I was unfamiliar with. Thanks for the education. Nature never ceases to amaze me.

Pamela Oglesby from Sunny Florida on May 11, 2019:

I did not think any frog looked quite like that, and this frog has very interesting features. Of course, since it lives in Australia I have never seen one, but living mostly undergrad and some of his features makes these frogs fascinating. Thanks for giving us so much informtion.

Linda Crampton (author) from British Columbia, Canada on May 10, 2019:

Thanks, Mel. You've raised a good point about the value of protecting our environmnent.

Mel Carriere from San Diego California on May 10, 2019:

Another fascinating creature you have described for us, that may have benefits to humanity. An added reason we should be more protective of our environment. Great article.

Linda Crampton (author) from British Columbia, Canada on May 10, 2019:

Thank you, Liz. I think that frogs are very interesting creatures.

Liz Westwood from UK on May 10, 2019:

We have a lot of frogs in the UK, but your fact file on this Australian frog is fascinating.

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