'Frogs as Bio-Indicators'
Science Corner

Welcome to the 'Frogs as Bio-indicators' Science Corner, a feature of the Thousand Friends of Frogs web site, which deals with the scientific aspects of amphibians and their environment. Choose from the following areas of interest:

Amphibian Facts
Minnesota Frogs and Toads
Global Amphibian Declines--Amphibians in Trouble!!
What are the frogs trying to tell us?--Malformed Amphibians
Student and School Reports--What Students are discovering!
'Frog'-quently Asked Questions
Malformed Frog and Toad Pictures

Amphibian Facts

When talking about frogs, toads or salamanders, you will probably have some questions. These are some basic facts about amphibians--frogs, toads, salamanders and caecilians. If you have further questions, check out the 'Frog'-quently Asked Questions section.

Q. What is an amphibian?

    A. Frogs, toads, salamanders and caecilians are all amphibians. The word means double life--many species spend part of their life in aquatic (water) and terrestrial (land) environments. Because their skin lacks a shell, scales or outer drier covering, most amphibians live in wet or damp situations to prevent dehydration.

Q. What is metamorphosis?

    A. Various animals undergo major changes in their body appearance and structure as they grow. They undergo meta (change) in their morpho (form). For instance, frogs lay eggs which grow into tadpoles, which undergo a dramatic change into froglets and finally grow to be an adult frog. The key thing in metamorphosis is a rapid, drastic change in form, for example from the tadpole to the frog.
    Butterflies are another example of animals that undergo metamorphosis, from a caterpillar to a flying butterfly.

Q. What is a Bio-indicator?

    A. A Bio-indicator is a living (bio means life) creature that is indicating or telling you something about the area that it lives in. It can be something positive (good) or negative (bad). For example, having lots of frogs in an area tells you and scientists that the environment is healthy and complete for the frogs. If for some reason frogs are suddenly missing from an area or their population is declining (shrinking), then this is telling you that their environment is changing. Sometimes bio-indicators can be used to show us that the quality of the air we breathe or water we drink may not be of a high quality.

Q. Why are frogs good bio-indicators?

    A. Frogs and other amphibians are good bio-indicators because

    • they spend part of their life cycle on land and some in water
    • have a permeable skin (which allows substances to move relatively freely into its body) and
    • absorb and concentrate (make stronger) toxins (poisonous substances) in their fatty tissues

Q. How long have amphibians been around?

    A. Amphibians have been around for an estimated 350 million years. The earliest known frog appeared about 190 million years ago, during what is known as the late Jurassic period.

Check out our 'Frog'-quently Asked Questions section for more information. For some other strange and interesting information on amphibians, check out this web site.

Minnesota Frogs and Toads
© 1998 Minnesota Department of Natural Resources

    Even though we distinguish in general terms between frogs and toads, apart from minor physical differences, frogs and toads are really the same. Herpetologists (scientists who study amphibians and reptiles) refer to frogs and toads as anurans.

    All anurans are appropriately called 'frogs' while 'toads' is reserved for specific families of anurans like Bufonidae (a common family of toads in N. America and other parts of the world).

    The 14 species of anurans found in Minnesota are grouped into three families: true frogs, treefrogs, and toads. Even though they are placed in three groups, each individual species (types) within each group has its own particular environment (or niche), unique breeding call, and survival mechanism.

Minnesota Frogs and Toads

Click on the name to get more information and see a photograph of each frog or toad. Click here to hear calls of some of Minnesota's frogs and toads. Click here for A Key to the Anuran Tadpoles of the United States and Canada.

Northern Leopard Frog
Green Frog
Wood Frog
Pickerel Frog
Mink Frog

Northern Cricket Frog
Spring Peeper
Gray TreeFrog
Cope's Gray TreeFrog
Western Chorus Frog

American Toad
Canadian Toad
Great Plains Toad

What Scientists are saying about Amphibian Populations in Minnesota

John Moriarty, Wildlife Specialist and Scientific Advisor to the project, reports on the Status of Amphibians in Minnesota.

Survey Results from
A Thousand Friends of Frogs
Student and Citizen Monitoring

Hundreds of students and citizens have again been assisting the Minnesota Pollution Control Agency (MPCA) gather data on the health of Minnesota's frog population during 1996, 1997 and 1998. Click here for the results of the survey.

Click here for surveying pictures.

'Frog'-quently Asked Questions

Here you can find answers to some of your questions about:

The Life of Frogs and Toads
The Anatomy of Frogs and Toads
Comparisons of Species
Deformed and Declining Amphibians


Choose from these other areas:

Amphibian Facts
Minnesota Frogs and Toads
Global Amphibian Declines--Amphibians in Trouble!!
What are the frogs trying to tell us?--Malformed Amphibians
Student and School Reports--What Students are discovering!
Frog-quently Asked Questions
Malformed Frog and Toad Pictures

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