There are countless animals without tails, and all of them fall under the category of "invertebrates." Invertebrates are animals that don't have backbones (and therefore don't have tails either). Some examples include centipedes, insects, grasshoppers, butterflies, snails, octopuses, spiders, worms and scorpions.
Animals can be divided into several different categories, but one simple way to categorize them is to divide them into one of two groups: invertebrates or vertebrates. Vertebrates have backbones, whereas invertebrates do not. Reptiles, fish, birds, amphibians and mammals fall into the vertebrate category. Vertebrates include lizards, salamanders, eagles, rabbits, cows, humans, etc. Most, but not all, animals in the vertebrate category have tails.
Although many invertebrates are so small that they are often overlooked, they comprise over 95 percent of the world's animal population. Tiny termites, minute millipedes, little leeches and small snails all fall into the invertebrate family.
Insects are a special type of invertebrate that have specific characteristics unlike others. Insects have a three-part body (a head, thorax and abdomen) and six legs. The head contains eyes and an apparatus for sucking and eating. The thorax has legs and sometimes wings as well. The abdomen contains vital organs, which are mainly those related to reproduction.