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Phylum:
Mandibulata
Insects are probably the most familiar of all invertebrates. They are easily identified by their 3 pairs of legs, and 3 main body parts, the head, thorax, and abdomen. Insects are protected by a hard exoskeleton made of chitin. Most insects have large compound eyes and antennae. The most primitive insect groups are wingless, although some advanced insect groups, like the fleas, have subsequently lost their wings.
Most
insects reproduce sexually, although some insects, like aphids, can reproduce
asexually. All insects lay eggs. In more primitive insects the newly hatched
offspring look very much like miniatures of their parents. However, a
significant advancement seen in some insects is the development of metamorphosis,
where the juveniles initially look very different from and must go through
a significant transformation in order to reach the adult stage.
Diversity of Insects
Insects are the most diverse group of animals. There are ~750,000 species of insects already described and conservative estimates suggest that there are 1.5 million species waiting to be discovered. Insects are most diverse in the tropics where the combination of high plant diversity and warm climates provides a great number of microhabitats. In the U.S. and Canada there are 91,000 known species and probably about 67,000 undescribed species.
The insects are divided into 32 orders according to morphological and genetic relationships. The four dominant orders, which include the majority of all species on Earth are the Coleoptera (beetles), Hymenoptera (bees, wasps, and ants), Lepidoptera (butterfllies, skippers, and moths), and Diptera (flies). By far, the Coleoptera are the most diverse species of animals, containing about 370,000 species, or 40% of all insects and 10% of all animals.
Most
beetles are easily recognized by the hardened elytra that cover and protect
their wings and abdomen. Most beetles are herbivorous or predaceous and
live in almost any habitat. With more than 10,000 species Lepidoptera
are the second most diverse group. The adults have scaled wings and their
mouthparts are modified for sucking nectar or fruit juices. The larvae
have chewingmouthparts and lack legs or antennae. Except for a single
predaceous species all caterpillars are herbivorous. Like the beetles,
the Hymenoptera vary greatly in body morphology and habitat types. There
are about 130,000 species known, may of which are wingless. Many Hymenoptera
live in social colonies and exhibit the most complex behavior of all insects.
There are about 120,000 species of Diptera. Similar to the Lepidoptera,
the mouthparts of adult mosquitos and flies are modified for sucking,
while the larvae's mouthparts are adapted for chewing.Although some flies
are responsible for transmission of disease most are extremely beneficial.
Many feed on decaying plants and animals.
Evolution of Insects
We know from fossilized specimens that insects were living 400 million years ago. They and the myriapods (millipedes and centipedes) are most likely decended from a segmented worm-like ancestor. The head, thorax, and abdomen of insects are formed from groups of fused segments. Insects are the first animals with the capability of flight and some scientists think that wings probably originated from insect gills. Shortly after the development of wings, about 330 million years ago, an explosion of insect species is seen in the fossil record, documenting the spread of insects into new habitat types. Today there are insects inhabiting almost every major ecosystem in the world except the oceans. There are even insects inhabiting Antarctica and in the Great Salt Lake.
Here are a few of the many great websites devoted to insects:
Entomology Department at Colorado State University provides a wonderful resource with photos, movies, and even information about careeers in insect biology.
Bugbios by Dexter Sear is a comprehensive site about everything insect, including photos, descriptions of the different insect groups and links to pages on insects and human society.
3D Bugs is a fun animation page with realistic insects from Virginia Tech. Requires free VRML download to run.
Butterflies of North America is a USGS link with photos and descriptions of common butterflies and links to butterflies in other states.
The Ants of North America is a key to the ants devloped by W. and E. Mackay at the University of Texas, El Paso
Biodiversity Topics: Introduction . Plants . Animals . Mammals . Birds . Reptiles & Amphibians . Arthropods . Spiders . Insects
© 2001-2004 The Cofrin Center
for Biodiversity and the University of Wisconsin Green Bay,
All Rights Reserved
Last
updated on
January 12, 2006