J: medial prolegs
K: anal proleg
(F, G, and H: true legs)
Lepidoptera: Papilio machaon caterpillar with 4 pairs of medial prolegs and a pair of anal prolegs
Hymenoptera: Craesus septentrionalis caterpillars with 7 pairs of prolegs

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 other larval insects such as sawflies and a few other types of insects. In all the orders in which they appear, mainly Hymenoptera and Lepidoptera, prolegs of any form evolved independently of each other by convergent evolution.[1] They appear to have evolved from ancient inactive genes that has since been activated again.[2]

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.[3] 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)[4]
Larvae ofGroup/
Family		OrderA1=S4A2=S5A3=S6A4=S7A5=S8A6=S9A7=S10A8=S11A9/10=S12/13
(anal proleg
pygopodium)		legs
total
incl T1–3
Butterflies/MothsmanyLepidoptera--2222--216
Archaic mothsMicropterygidaeLepidoptera22222222224
Owlet mothsNoctuidae (some)Lepidoptera---222--214
Owlet mothsNoctuidae (some)Lepidoptera----22--212
Geometer mothsGeometridaeLepidoptera-----2--210
SawfliesSymphyta (many)Hymenoptera-2222222222
SawfliesSymphyta (some)Hymenoptera-222222-220
SawfliesSymphyta (some)Hymenoptera-22222--218
some? PamphiliidaePamphiliinaeHymenoptera--------28
MecopteraallMecoptera22222222224
CaddisfliesallTrichoptera--------28

See also

References

  1. ↑ Suzuki, Y.; Palopoli, M. (2001). "Evolution of insect abdominal appendages: Are prolegs homologous or convergent traits?". Development Genes and Evolution. 211 (10): 486–492. doi:10.1007/s00427-001-0182-3. PMID 11702198. S2CID 1163446.
  2. ↑ Lepidopteran prolegs are novel traits, not leg homologs
  3. ↑ Richards, O. W.; Davies, R.G. (1977). Imms' General Textbook of Entomology: Volume 1: Structure, Physiology and Development Volume 2: Classification and Biology. Berlin: Springer. ISBN 0-412-61390-5.
  4. ↑ Stefan von Kéler: Entomologisches Wörterbuch. Akademie-Verlag Berlin 1963. p. 80.
  • 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.
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