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The pupal stage of an insect's life is both mysterious and miraculous. What appears to be a motionless, nearly lifeless form is actually an insect undergoing a remarkable transformation. Although you can't see what occurs within a cocoon, you can understand a bit more about the process of metamorphosis by learning the differences between pupal forms.
Only insects that undergo complete metamorphosis have a pupal stage. We use five terms to describe the types of insect pupae, but for some insects, more than one term may apply to its pupal form. A pupa may be both exarate and decticous, for example.
Let's learn how each of these pupal forms is differentiated and how they may overlap.
In obtect pupae, the insect's appendages are fused or "glued" to the body wall as the exoskeleton hardens. Many obtect pupae are enclosed within a cocoon.
Obtect pupae occur in many of the Diptera order of insects (true bugs). This includes midges, mosquitoes, crane flies, and other members of the suborder Nematocera. Obtect pupae are also found in most Lepidoptera (butterflies) and in a few of the Hymenoptera (ants, bees, wasps) and Coleoptera (beetles).
Gilles San Martin/Flickr/CC BY 2.0
Exarate pupae are just the opposite of obtect pupae. The appendages are free and they can move (though they usually remain inactive). Movement is usually limited to the abdominal segments, but some can also move their appendages.
An exarate pupa usually lacks a cocoon, and looks like a pale, mummified adult, according to "Borror and DeLong's Introduction to the Study of Insects." Most pupae fall into this category.
Nearly all insects that undergo complete metamorphosis have exarate pupae.
gailhampshire/Flickr/CC BY 2.0
Decticous pupae have articulated mandibles, which they may use to chew through the pupal cell. Decticous pupae tend to be active, and are always also exarate with free appendages.
Decticous and exarate pupae include members of Mecoptera (scorpionflies and hanging flies), Neuroptera (nerve-winged insects), Trichoptera (caddisflies), and some primitive Lepidoptera.
Ryan Hodnett/Wikimedia Commons/CC BY 4.0
Adecticous pupae lack functional mandibles and cannot chew their way out of the pupal case or bite in defense. The mandibles are attached to the head in such a way as to render them immobile.
Adecticous pupae may also be either obtect or exarate.
Adecticous obtect pupae include members of the following insect groups: Diptera, Lepidoptera, Coleoptera, and Hymenoptera.
Adecticous exarate pupae include members of the following insect groups: Siphonaptera (fleas), Strepsiptera (twisted-wing parasites), Diptera, Coleoptera, and Hymenoptera.
Coarctate pupae are covered by a membrane called a puparium, which is actually the hardened cuticle of the final larval instar (stage of molting). Because these pupae have free appendages, they are also considered exarate in form.
Coarctate pupae are found in many families of Diptera (suborder Brachycera).
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