Mecoptera

Mecoptera

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Encyclopedia
Mecoptera are an order of insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s with about 550 species in nine families worldwide. Mecoptera are sometimes called scorpionflies after their largest family, Panorpidae, in which the males have enlarged genitals that look similar to the stinger of a scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...

. The Bittacidae, or hangingflies, are a prominent family of elongate insects known for their elaborate mating rituals, in which females choose mates based on the quality of gift prey offered by various males.

While modern mecoptera are overwhelmingly
predators or consumers of dead organisms, early ones might have played an important role before the evolution of other insects in pollinating extinct gymnosperm
Gymnosperm
The gymnosperms are a group of seed-bearing plants that includes conifers, cycads, Ginkgo, and Gnetales. The term "gymnosperm" comes from the Greek word gymnospermos , meaning "naked seeds", after the unenclosed condition of their seeds...

s.

Anatomy and biology


Mecoptera are small to medium insects with slender, elongated, bodies. They have relatively simple mouthparts, with long mandible
Mandible (arthropod)
thumb|250px|The mandibles of a [[Bull ant]]The mandible of an arthropod is either of a pair of mouthparts used for biting, cutting and holding food. Mandibles are often simply referred to as jaws. Mandibles are present in the extant subphyla Myriapoda , Crustacea and Hexapoda...

s and fleshy palps, which resemble those of the more primitive true flies
Diptera
Diptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...

. Like many other insects, they possess compound eyes on the side of the head, and three ocelli on the top. Most Mecoptera feed on vegetation in moist environments; in hotter climates, they may therefore be active only for short periods of the year.

The wings are narrow in shape, with numerous cross-veins, and somewhat resemble those of primitive insects such as mayflie
Mayfly
Mayflies are insects which belong to the Order Ephemeroptera . They have been placed into an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies...

s. A few genera, however, have reduced wings, or have lost them altogether. The abdomen is cylindrical, and typically curves upwards in the male, superficially resembling the tail of a scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...

.

The female lays the eggs in close contact with moisture, and the eggs typically absorb water and increase in size after deposition. In species that live in hot conditions, the eggs may not hatch for several months, the larvae only emerging when the dry season has finished. More typically, however, they hatch after a relatively short period of time.

The larvae are usually quite caterpillar
Caterpillar
Caterpillars are the larval form of members of the order Lepidoptera . They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture...

-like, with short, clawed, true legs, and a number of abdominal proleg
Proleg
A Proleg is the small fleshy, stub structure found on the ventral surface of the abdomen of most larval forms of insects of the order Lepidoptera, though they can also be found on other larval insects such as sawflies and a few types of flies....

s. They have a sclerotised head with compound eyes and mandibulate mouthparts. The tenth abdominal segment bears either a suction disc, or, less commonly, a pair of hooks. They generally eat vegetation or scavenge for dead insects, although some predatory larvae are known.

The larva crawls into the soil or decaying wood to pupa
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...

te, and does not spin a cocoon. The pupae are exarate, meaning that the limbs are free of the body, and are able to move their mandibles, but are otherwise entirely non-motile. In drier environments, they may spend several months in diapause
Diapause
Diapause is the delay in development in response to regularly and recurring periods of adverse environmental conditions. It is considered to be a physiological state of dormancy with very specific initiating and inhibiting conditions...

, before emerging as adults once the conditions are more suitable.

Evolution


DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 evidence indicates that flea
Flea
Flea is the common name for insects of the order Siphonaptera which are wingless insects with mouthparts adapted for piercing skin and sucking blood...

s, which are traditionally considered a separate order (Order Siphonaptera), are instead highly specialized Mecoptera. Grouped together with the fleas, Mecoptera would have about 3000 known species.

Mecoptera have special importance in evolution of Insecta. Two of the most important insect orders, Lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...

 and Diptera
Diptera
Diptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...

, along with Trichoptera
Trichoptera
The caddisflies are an order, Trichoptera, of insects with approximately 12,000 described species. Also called sedge-flies or rail-flies, they are small moth-like insects having two pairs of hairy membranous wings...

, probably evolved from ancestors belonging to, or strictly related to, the Mecoptera. This is apparent from anatomical and biochemical similarities, but, moreover, transitional fossil
Transitional fossil
A transitional fossil is any fossilized remains of a lifeform that exhibits characteristics of two distinct taxonomic groups. A transitional fossil is the fossil of an organism near the branching point where major individual lineages diverge...

s, such as Permotanyderus and Choristotanyderus, have been discovered that lie between the Mecoptera and Diptera.

The group was once much more widespread and diverse than at present, having as many as four suborders during the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...

.

First pollinators


It has been proposed that extinct mecoptera species were important plant pollinators. Early non-angiosperm gymnosperm
Gymnosperm
The gymnosperms are a group of seed-bearing plants that includes conifers, cycads, Ginkgo, and Gnetales. The term "gymnosperm" comes from the Greek word gymnospermos , meaning "naked seeds", after the unenclosed condition of their seeds...

 seed plants during the late Middle Jurassic to mid–Early Cretaceous period have been believed to be mainly wind-pollinated. However examination of fossil mecoptera show that they had siphon feeding apparatus that could fertilize early gymnosperms by feeding on their nectar and pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...

. The lack of iron enrichment in their fossilized proboscis
Proboscis
A proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In simpler terms, a proboscis is the straw-like mouth found in several varieties of species.-Etymology:...

 rules out a use in blood drinking. One question over this suggestion is that so far pollen has not been found associated with these feeding parts which is surprising for the amber-encased insects which should have preserved pollen but "further fossils may provide this information".

11 species have been identified belonged to three families, Mesopsychidae, Aneuretopsychidae, and Pseudopolycentropodidae for which "the encompassing name Aneuretopsychina is available". Their length ranges from 3 mm in Parapolycentropus burmiticus to 28 mm in Lichnomesopsyche gloriae. The proboscis could be as long as 10 mm. Pollen transfer has been suggested to occur by body surface transport on mouthpart and head surfaces like that in bee flies and hover flies—however no such associated pollen has been found even though the insects were preserved in amber
Amber
Amber is fossilized tree resin , which has been appreciated for its color and natural beauty since Neolithic times. Amber is used as an ingredient in perfumes, as a healing agent in folk medicine, and as jewelry. There are five classes of amber, defined on the basis of their chemical constituents...

. It is thought that they pollinated such plants as Caytoniaceae, Cheirolepidiaceae
Cheirolepidiaceae
Cheirolepidiaceae is a family of extinct coniferous plants.This family of conifers, superficially similar to Cupressaceae, was a significant part of the flora of the Mesozoic, around . They are united by the possession of a distinctive pollen type assigned to the form genus Classopollis...

, Czekanowskiaceae, Pentoxylaceae, and Gnetales as these have ovulate organs that are either poorly suited for wind pollination or have structures that could support long-proboscid fluid feeding.

Mating


Gullen and Cranston offer a startling description of the mating habits of the Bittacidae:

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