A proleg is a 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 larvae of insects such as sawflies.
Variations
In all the orders in which they appear, mainly Hymenoptera and Lepidoptera, prolegs of any form evolved independently of each other by convergent evolution. They appear to have evolved from ancient inactive genes that have since been activated again.Lepidopteran prolegs are novel traits, not leg homologs
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 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
Number of prolegs on insect larvae at abdominal segments A1–A9/10=S4-12/13 (T1–3: thorax segments with 6 legs)Stefan von Kéler: Entomologisches Wörterbuch. Akademie-Verlag Berlin 1963. p. 80. Larvae of Group/Family Order A1=S4 A2=S5 A3=S6 A4=S7 A5=S8 A6=S9 A7=S10 A8=S11 A9/10=S12/13(anal prolegpygopodium) legstotalincl T1–3Butterflies/MothsmanyLepidoptera--2222--216Archaic mothsMicropterygidaeLepidoptera22222222224Owlet moths and alliesNoctuoidea (some)Lepidoptera---222--214Owlet moths and alliesNoctuoidea (some)Lepidoptera----22--212Geometer mothsGeometridaeLepidoptera-----2--210Geometer mothsGeometridae (very few species)Lepidoptera----22--212SawfliesSymphyta (many)Hymenoptera-2222222222SawfliesSymphyta (some)Hymenoptera-222222-220SawfliesSymphyta (some)Hymenoptera-22222--218some? PamphiliidaePamphiliinaeHymenoptera--------28MecopteraallMecoptera22222222224CaddisfliesallTrichoptera--------28
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?