During its larval stage an insect which undergoes complete metamorphosis may go through a number of molts as it grows. With the final molt the insect becomes a pupa. Dukas, Reuven (1 January 2008). "Evolutionary Biology of Insect Learning". Annual Review of Entomology. 53 (1): 145–160. doi: 10.1146/annurev.ento.53.103106.093343. PMID 17803459. Insects are members of a subgroup of arthropods known as Hexapoda, whose name comes from the Greek for ‘six legs’. Braak, Nora; Neve, Rebecca; Jones, Andrew K.; Gibbs, Melanie; Breuker, Casper J. (November 2018). "The effects of insecticides on butterflies – A review". Environmental Pollution. 242 (Pt A): 507–518. doi: 10.1016/j.envpol.2018.06.100. PMID 30005263. S2CID 51625489.

Ruppert, E. E.; Fox, R. S.; Barnes, R. D. (2004). Invertebrate Zoology (7thed.). Brooks / Cole. pp. 523–524. ISBN 978-0-03-025982-1. There are two main forms of insect metamorphosis: incomplete metamorphosis (also known as partial metamorphosis, or hemimetaboly), and complete metamorphosis (holometaboly). Incomplete Metamorphosis Although traditionally grouped with millipedes and centipedes, [22] more recent analysis indicates closer evolutionary ties with crustaceans. In the Pancrustacea theory, insects, together with Entognatha, Remipedia, and Cephalocarida, form a clade, the Pancrustacea. [23] Insects form a single clade, closely related to crustaceans and myriapods. [24] The ovipositors of several insect groups, including many wasp, bee and ant species, have been modified into stingers. An insect’s stinger is a modified ovipositor.There are many different patterns of gas exchange demonstrated by different groups of insects. Gas exchange patterns in insects can range from continuous and diffusive ventilation, to discontinuous gas exchange. [31] :65–68 During continuous gas exchange, oxygen is taken in and carbon dioxide is released in a continuous cycle. In discontinuous gas exchange, however, the insect takes in oxygen while it is active and small amounts of carbon dioxide are released when the insect is at rest. [78] Diffusive ventilation is simply a form of continuous gas exchange that occurs by diffusion rather than physically taking in the oxygen. Some species of insect that are submerged also have adaptations to aid in respiration. As larvae, many insects have gills that can extract oxygen dissolved in water, while others need to rise to the water surface to replenish air supplies, which may be held or trapped in special structures. [79] [80] Circulatory system Johnson, K. P.; Yoshizawa, K.; Smith, V. S. (2004). "Multiple origins of parasitism in lice". Proceedings of the Royal Society of London. 271 (1550): 1771–1776. doi: 10.1098/rspb.2004.2798. PMC 1691793. PMID 15315891. Theiss, Joachim (1982). "Generation and radiation of Lee, Richard E. Jr. (1989). "Insect Cold-Hardiness: To Freeze or Not to Freeze" (PDF). BioScience. 39 (5): 308–313. doi: 10.2307/1311113. JSTOR 1311113. Archived (PDF) from the original on 10 January 2011 . Retrieved 2 December 2009. Frequently Asked Questions on Entomology | Entomological Society of America (ESA)". 7 February 2015. Archived from the original on 7 February 2015 . Retrieved 19 July 2021.

Kapoor, V.C.C. (1998). Principles and Practices of Animal Taxonomy. Vol.1 (1sted.). Science Publishers. p.48. ISBN 978-1-57808-024-3. Kendall, David A. (2009). "Classification of Insect". Archived from the original on 20 May 2009 . Retrieved 9 May 2009. Lozano-Fernandez, Jesus; Giacomelli, Mattia; Fleming, James F.; Chen, Albert; Vinther, Jakob; Thomsen, Philip Francis; Glenner, Henrik; Palero, Ferran; Legg, David A.; Iliffe, Thomas M.; Pisani, Davide; Olesen, Jørgen (2019). "Pancrustacean Evolution Illuminated by Taxon-Rich Genomic-Scale Data Sets with an Expanded Remipede Sampling". Genome Biology and Evolution. 11 (8): 2055–2070. doi: 10.1093/gbe/evz097. PMC 6684935. PMID 31270537. Some insects display a rudimentary sense of numbers, [97] such as the solitary wasps that prey upon a single species. The mother wasp lays her eggs in individual cells and provides each egg with a number of live caterpillars on which the young feed when hatched. Some species of wasp always provide five, others twelve, and others as high as twenty-four caterpillars per cell. The number of caterpillars is different among species, but always the same for each sex of larva. The male solitary wasp in the genus Eumenes is smaller than the female, so the mother of one species supplies him with only five caterpillars; the larger female receives ten caterpillars in her cell. Hymenoptera (Ants, Bees and Wasps) Tarantula hawk wasp. These wasps have one of the most painful stings of all insects.The individual lenses in compound eyes are immobile, and it was therefore presumed that insects were not able to focus. But research on fruit flies, which is the only insects studied so far, has shown that photoreceptor cells underneath each lens move rapidly in and out of focus in a series of movements called photoreceptor microsaccades. This gives them a much clearer image of the world than previously assumed. [102] Sound production and hearing Cator, L.J.; Arthur, B.J.; Harrington, L.C.; Hoy, R.R. (2009). "Harmonic convergence in the love songs of the dengue vector mosquito". Science. 323 (5917): 1077–1079. Bibcode: 2009Sci...323.1077C. doi: 10.1126/science.1166541. PMC 2847473. PMID 19131593. Duncan, Carl D. (1939). A Contribution to The Biology of North American Vespine Wasps (1sted.). Stanford: Stanford University Press. pp.24–29.