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Blue Butterfly

What is an Invertebrate?

To identify an animal as an invertebrate, it should have these characteristics:

  • Invertebrates have no backbone!  Any animal that doesn't have a spine is an invertebrate.
  • Invertebrates are cold-blooded. They cannot regulate their own body temperature.

That's it!  There are so many different types of invertebrates that making a list of uniting characteristics is almost impossible. 

Invertebrates are a very diverse group of species, including:

  • Insects
  • Spiders
  • Crustaceans (lobsters and crabs)
  • Worms
  • Mollusks (squids, snails and clams)
  • Coral

How are Invertebrates Doing Worldwide and in the U.S.?


Invertebrates are the most diverse and numerous species on Earth. According to the International Union for Conservation of Nature (IUCN), over 1.3 million invertebrates have been identified as of 2009. They make up approximately 75% of the known species on Earth.

The actual number of invertebrates on Earth is unknown. Some predict that there could be tens of millions of invertebrates, with the majority being insects.  We just don't know – scientists are identifying new species all the time and expanding our knowledge daily. Even more worrying is that because we have insufficient data, invertebrates could be going extinct and we would not even know they existed.

There are over 140,000 invertebrates in the United States--a number that is growing as researchers identify more and more species. Of the 140,000 plus species in the U.S., there are approximately 200 invertebrates on the Endangered Species List.

Many of the invertebrates on the Endangered Species List are unknown to the public, because they naturally have small ranges and are difficult to identify. The most recognizable invertebrates on the Endangered Species List include, the Karner blue butterfly, blackburn's sphinx moth, and the oyster mussel.



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