proleg

{{Short description|Anatomical structure}}

File:Caterpillar-description.jpg

File:Chenille de Grand porte queue (macaon) Fausses pattes.jpg caterpillar with four pairs of medial prolegs and a pair of anal prolegs]]

File:Craesus septentrionalis.jpg caterpillars with seven 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 larvae of insects such as sawflies. In all the orders in which they appear, mainly Hymenoptera and Lepidoptera, prolegs of any form evolved independently of each other by convergent evolution.{{Cite journal | last1 = Suzuki | first1 = Y. | last2 = Palopoli | first2 = M. | doi = 10.1007/s00427-001-0182-3 | title = Evolution of insect abdominal appendages: Are prolegs homologous or convergent traits? | journal = Development Genes and Evolution | volume = 211 | issue = 10 | pages = 486–492 | year = 2001 | pmid = 11702198| s2cid = 1163446 }} They appear to have evolved from ancient inactive genes that have since been activated again.[https://www.science.org/doi/10.1126/sciadv.add9389 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.{{cite book |author1=Richards, O. W. |author2=Davies, R.G. |title=Imms' General Textbook of Entomology: Volume 1: Structure, Physiology and Development Volume 2: Classification and Biology |publisher=Springer |location=Berlin |year=1977 |isbn=0-412-61390-5 }} 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.