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Insect Identification Key
Order Diptera: the true flies

Two wings
Notice that this fly has only two wings. This is a telltale characteristic of flies. Photo credit: Leslie Mertz.

Click here to see examples of more flies!

Based on your answers to the questions, you have identified your insect as being in the order Diptera!

Members of this order include: house flies, deer flies, crane flies, mosquitoes, no-see-ums and other tiny midges, horse flies, and many more.

Etymology: Diptera comes from the Greek words di, which means two, and ptera, which means wings. Diptera, therefore, means “two-winged.”

General characteristics:
• one pair of membranous wings. These are forewings.
• presence of halteres, which are small balancing organs located behind the front wings. Halteres are tiny knobbed structures. The halteres are actually reduced and modified hind wings. While a few insects other than flies that have only one pair of wings, none of them have halteres.
• soft body
• body that is often covered with short bristles
• depending on the species of fly, the mouthparts may be used for sucking, for lapping up fluids or for piercing into a prey animal
thorax that is enlarged in the middle to give it a rather hunch-backed look
holometabolous metamorphosis (egg — larvapupa — adult)

Click here to see examples of more flies!

Number of species worldwide: 120,000

Kingdom Animalia
   Phylum Arthropoda
      Class Insecta
         Order Diptera

For a list of all of the orders in this key, click here: List of Orders.

Classification note: Some insects have the word “fly” in their names, but aren’t actually true flies. For instance, dragonflies and fireflies are not in the order Diptera. Notice that dragonfly and firefly are one word, whereas true flies, such as the house fly, crane fly and horse fly, are all two words.

Oops! If this doesn’t appear to be the order for your insect, go back through the key and look more carefully at your insect while answering the questions again. Your perseverance will reward you!

I would like to return to the start of this key.

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Unless noted otherwise, photographs on this website are the property of the photographers and may not be reused without written permission from the photographers. To obtain permission, request it here.

Photos at the top of this website are (from left to right): potato beetle (Leptinotarsa decemlineata) — photo credit: Scott Bauer, U.S. Department of Agriculture; ebony jewelwing (Calopteryx maculata)— photo credit: U.S. Fish and Wildlife Service; sweat bee (Agapostemon splendens) — photo credit: Natalie Allen and Stephanie Kolski, U.S. Geological Survey; preying mantis, monarch butterfly (Danaus plexippus), hellgrammite (aka toe biter) larva and eyed click beetle (Alaus oculatus) — photo credit: Leslie Mertz; Halloween pennant (Celithemis eponina) — photo credit: Kay Meng, U.S. Fish and Wildlife Service.

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