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A proleg is a small, fleshy, stub structure found on the ventral surface of the
abdomen The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...
of most
larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...
l forms of
insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...
s of the
order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...
Lepidoptera Lepidoptera ( ) or lepidopterans is an order (biology), order of winged insects which includes butterflies and moths. About 180,000 species of the Lepidoptera have been described, representing 10% of the total described species of living organ ...
, though they can also be found on larvae of insects such as
sawflies Sawflies are wasp-like insects that are in the suborder Symphyta within the order Hymenoptera, alongside ants, bees, and wasps. The common name comes from the saw-like appearance of the ovipositor, which the females use to cut into the plant ...
. In all the orders in which they appear, mainly
Hymenoptera Hymenoptera is a large order of insects, comprising the sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are parasitic. Females typi ...
and Lepidoptera, prolegs of any form evolved independently of each other by
convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...
. They appear to have evolved from ancient inactive genes that have since been activated again.Lepidopteran prolegs are novel traits, not leg homologs
/ref> Prolegs of lepidopteran larvae have a small circle of gripping hooks, called "crochets". The arrangement of the crochets can be helpful in identification to
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
level. Although the point has been debated, prolegs are not widely regarded as true legs, derived from the primitive uniramous limbs. Certainly in their morphology they are not jointed, and so lack the five segments (coxa, trochanter, femur, tibia, tarsus) of thoracic insect legs. Prolegs do have limited musculature, but much of their movement is hydraulically powered.


Number of prolegs for various insect larvae

Additional (stubby) prolegs on segment 8 have been reported on the Geometridae species Campaea perlata and Alsophila pometaria.


See also

* Terrestrial locomotion in animals


References

* Peterson, A. 1948. ''Larvae Of Insects. Part I: Lepidoptera & Hymenoptera; Part II: Coleoptera, Diptera, Neuroptera, Siphonaptera, Mecoptera, Trichoptera.'' Columbus, OH. * Richards, O.W. & R.G. Davies. 1977. ''Imm's General Textbook of Entomology'', 10th ed. (2 Volumes). Chapman & Hall, London. * Snodgrass, R.E. 1935 (1993 reprint). ''Principles of Insect Morphology''. Cornell University Press, Ithaca, NY.


External links


How Many Legs Do Caterpillars Have?
Insect anatomy Larvae {{Insect-anatomy-stub