Orthoptera

Orthoptera (from the Greek orthos, "straight," and pteron, "wing") is an order of hemimetabolous (incomplete-metamorphosis) neopteran insects inside superorder Polyneoptera comprising more than 29,000 described extant species of grasshoppers, locusts, crickets, katydids (bush-crickets), wetas, Jerusalem crickets, and mole crickets. Originating in the Late Carboniferous (~310 million years ago), orthopterans are defined by two universal anatomical and behavioral synapomorphies:

1. Saltatorial Hind Legs: Enlarged, heavily muscled metathoracic femora and elongated tibiae coupled to a semilunar cuticular spring made of resilin and sclerotized chitin that stores and releases elastic strain energy for ballistic jumping.
2. A Saddle-Shaped Pronotum and Coriaceous Forewings (Tegmina): A prominent dorsal thoracic shield (pronotum) that extends laterally over the pleura, paired with narrow, leathery forewings (tegmina) that protect the broad, fan-folded membranous hindwings at rest and frequently bear specialized file-and-scraper structures for acoustic stridulation.

Orthopterans are partitioned into two monophyletic suborders—Ensifera (crickets, katydids, wetas; long antennae and blade- or needle-like ovipositors) and Caelifera (grasshoppers, locusts, pygmy mole crickets; short antennae and short, digging ovipositors)—and constitute dominant primary consumers across global grassland, savanna, and forest-canopy ecosystems, as well as the world's most destructive migratory agricultural pests during locust phase polyphenism outbreaks.

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Molecular phylogenomics and fossil calibrations resolve a basal Permian–Carboniferous divergence between the two orthopteran suborders:

` Orthoptera (Late Carboniferous, ~310 Ma) ├── Suborder Ensifera (Long-horned Orthoptera: >16,000 species; antennae >30 segments) │ ├── Infraorder Gryllidea │ │ ├── Gryllidae (True crickets: Gryllus, Acheta domesticus, Teleogryllus) │ │ ├── Gryllotalpidae (Mole crickets: fossorial forelegs & acoustic burrows) │ │ └── Mogoplistidae & Myrmecophilidae (Scaly & ant-loving crickets) │ └── Infraorder Tettigoniidea │ ├── Tettigoniidae (Katydids / bush-crickets: >8,000 spp., leaf mimicry) │ ├── Anostostomatidae & Rhaphidophoridae (Wetas & cave crickets) │ └── Stenopelmatidae (Jerusalem crickets) │ └── Suborder Caelifera (Short-horned Orthoptera: ~13,000 species; antennae <30 segments) ├── Infraorder Tridactylidea (Pygmy mole crickets; water-surface jumping paddles) ├── Infraorder Tetrigidea (Tetrigidae: pygmy grasshoppers with elongated pronotum) └── Infraorder Acrididea ├── Pyrgomorphidae (Gaudy grasshoppers: cardenolide chemical defense) └── Acrididae (Short-horned grasshoppers & locusts: >10,000 spp., Schistocerca, Locusta)

Direct muscle contraction cannot generate the mechanical power required to accelerate a 2-gram grasshopper (Schistocerca gregaria) to take-off velocities of 3.0–3.2 m/s in less than 25–30 milliseconds (requiring an effective power output exceeding 10,000–15,000 W/kg of muscle, roughly 10 to 15 times the maximum isotonic power of striated insect muscle). Orthopterans solve this constraint through a tri-phasic elastic catapult mechanism at the femoro-tibial joint:

1. Initial Flexion (Cocking Phase): The weak tibial flexor muscle contracts to pull the hind tibia fully flexed against the ventral surface of the femur. At full flexion, the mechanical leverage (moment arm) of the flexor muscle increases relative to the massive tibial extensor muscle (which occupies ~75% of the femoral volume and inserts on a long apodeme) because the extensor apodeme slides over a distal femoral lump (Heitler's lump), creating a geometric catch lock.
2. Isometric Co-Contraction (Energy Storage Phase, ~200–500 ms): Both the tibial flexor and the massive pennate tibial extensor muscle contract simultaneously (co-contraction). Because the flexor holds the tibia locked in place via its mechanical advantage over Heitler's lump, the extensor muscle contracts nearly isometrically, stretching the semilunar processes—paired crescent-shaped arches of heavily sclerotized cuticle and elastomeric resilin at the distal femoro-tibial joint—together with the extensor apodeme. Each hind leg stores ~4–7 millijoules of elastic strain energy.
3. Trigger Release (Ballistic Extension, ~25 ms): Sudden inhibition of the flexor motor neurons releases the geometric catch. The stored elastic energy in the semilunar processes and extensor apodeme recoils, catapulting the tibia through a 140° arc and launching the insect up to 20–30 body lengths into the air at accelerations of 15–20 g.

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Orthoptera evolved complex acoustic communication early in the Mesozoic (with preserved stridulatory veins documented in Jurassic Archaboilus fossils ~165 Ma):

• Ensiferan Tegmino-Tegminal Stridulation: In male crickets (Gryllidae) and katydids (Tettigoniidae), the base of one forewing bears a hardened sclerotized ridge lined with 50 to 300 microscopic cuticular teeth (the file, or pars stridens), while the margin of the opposite forewing forms a sharp plectrum (the scraper). As the wings close, the scraper strikes each tooth of the file sequentially, exciting resonant vibrations in specialized membranous wing cells—the harp and mirror—which radiate narrow-band carrier frequencies (typically 3–8 kHz in field crickets; 10–150 kHz into the ultrasonic spectrum in neotropical katydids such as Supersonus, which achieve 150 kHz via an enclosed cavity resonator).
• Dolbear's Law (Thermometric Chirp Rate): Because orthopterans are ectothermic, the central pattern generator in the thoracic ganglia governing wing-closing muscle contraction scales via Arrhenius kinetics with ambient temperature, allowing ambient temperature to be estimated directly from the chirp cadence of snowy tree crickets (Oecanthus fultoni).
• Acoustic Burrows in Mole Crickets: Male mole crickets (Gryllotalpa vineae) excavate exponentially flared, double-mouthed horn-shaped burrows in damp soil tuned to the fundamental frequency of their calling song (~3.5 kHz), increasing acoustic radiation efficiency from ~1% to >30% and generating sound pressure levels of 90–96 dB SPL at 1 meter.
• Katydid Auditory Crista Acustica (Convergent Cochlea): Within the proximal fore-tibia of katydids, the crista acustica contains a linear array of 20 to 60 mechanosensory scolopidial neurons arranged along a tapered lipid-filled acoustic chamber (acoustic vesicle) and a tympanal membrane possessing impedance-matching lever mechanics and traveling-wave tonotopic frequency decomposition strikingly convergent with the mammalian inner-ear basilar membrane and organ of Corti.

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Approximately 20 species within the family Acrididae—most notably the desert locust (Schistocerca gregaria) and the migratory locust (Locusta migratoria)—are true locusts capable of density-dependent phase polyphenism, an extreme reversible phenotypic plasticity in which a single genotype transitions between two distinct morphological, neurochemical, and behavioral syndromes:

• Solitarious Phase (solitaria): At low population densities, nymphs are cryptic green or brown, avoid conspecifics, walk slowly, have shorter wings and longer hind femora, and feed individually at night or dawn.
• Gregarious Phase (*gregaria`): Triggered when drought forces locusts into patchy vegetation clumps:
  1. Mechanosensory and Olfactory Triggers: Repeated physical jostling of mechanosensory trichoid sensilla on the outer surface of the hind femora (requiring only 4 hours of stimulation in S. gregaria), or multimodal visual and olfactory stimulation in the antennae, induces an immediate surge in serotonin (5-hydroxytryptamine, 5-HT) in the thoracic ganglia (or dopamine and catecholamine pathways in L. migratoria).
  2. Pheromonal Aggregation (4-Vinylanisole): Gregarious locusts release the volatile aggregation pheromone 4-vinylanisole (4VA), detected by the odorant receptor OR35 on basiconic sensilla of the antennae once as few as 4 to 5 individuals congregate, creating a positive feedback loop that recruits solitary conspecifics.
  3. Epigenetic and Maternal Respecification: Within hours, solitary repulsion flips to mutual attraction. Across molts and into subsequent generations (mediated by foam-plug pheromones and small RNAs deposited by gregarious mothers into egg pods), locusts develop aposematic black-and-yellow/orange pigmentation, a broader saddle-shaped pronotum, a 30% larger brain (with expanded mushroom bodies for complex visual and social processing alongside reduced primary olfactory lobes), diurnal synchronized marching in hopper bands, and long-distance wind-borne adult swarms containing 40–80 million individuals per square kilometer capable of consuming the daily food equivalent of 35,000 humans per km².

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1. Song, H., et al. (2020). Phylogenomic analysis sheds light on the evolutionary pathways towards acoustic communication in Orthoptera. Nature Communications, 11, 4939. Google Scholar
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3. Anstey, M. L., Rogers, S. M., Ott, S. R., Burrows, M., & Simpson, S. J. (2009). Serotonin mediates behavioral gregarization underlying swarm formation in desert locusts. Science, 323(5914), 627–630. Google Scholar
4. Guo, X., et al. (2020). 4-Vinylanisole is an aggregation pheromone in locusts. Nature, 584(7822), 584–588. Google Scholar

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• Insecta
• Hemiptera
• Odonata
• Blattodea
• Sensory Transduction