Ancient-lineage
Guides
Amblyoponinae
Dracula ants, Vampire ants
Amblyoponinae is an ancient, relictual subfamily of ants characterized by specialized subterranean predatory habits and unique 'Dracula ant' behavior, in which adult workers pierce the integument of their own larvae to imbibe haemolymph. The subfamily contains 13 extant genera and originated in the mid-Cretaceous approximately 107 million years ago. Crown group diversification occurred in the Late Paleocene/Early Eocene. The subfamily exhibits remarkable morphological and behavioral diversity, including convergent evolution of army ant-like behaviors in some lineages and highly plastic caste systems in others.
Ankothrips
Ankothrips is a genus of thrips in the family Melanthripidae. It is recognized as the most ancient extant thrips genus, with fossil evidence indicating an origin in the Early Cretaceous period approximately 94 million years ago. The genus exhibits remarkable morphological stability over this timespan, with two fossil species described from French amber: Ankothrips dupeae from the Late Cretaceous and Ankothrips deploegi from the earliest Eocene. This long-term morphological conservatism is rare among insects.
Arenivaga floridensis
Florida Sand Cockroach
Arenivaga floridensis is a sexually dimorphic, fossorial sand cockroach endemic to Florida scrub ecosystems. It is the most geographically widespread faunal endemic of Florida scrub, documented from 11 peninsular sand ridges. Genetic analysis reveals three major mitochondrial lineages whose divergence corresponds with late Pliocene peninsula insularization, supporting a western origin hypothesis with colonization during the Pliocene or earlier. The species exhibits extreme sexual dimorphism: males possess fully developed wings and engage in low, erratic flight at dusk, while females are completely wingless and remain entirely fossorial throughout life. Its distribution is restricted to friable, sandy soils beneath light leaf litter of sand live oaks (Quercus geminata).
Buemarinoidae
Buemarinoid Harvestmen
Buemarinoidae is a small family of harvestmen (Opiliones: Laniatores) comprising approximately six genera and six described species. The family belongs to the superfamily Triaenonychoidea, which contains over 440 species across four families. Buemarinoidae is considered an ancient, relictual lineage with a disjunct global distribution and a high prevalence of monotypic genera, suggesting significant historical extinction events.
Cymbiodyta
Cymbiodyta is a genus of water scavenger beetles (Hydrophilidae: Enochrinae) comprising 31 described species. The genus exhibits a strikingly disjunct distribution: 28 species occur in the Americas, while only three species inhabit the Palearctic region. A fossil species from Eocene Baltic amber (C. samueli) confirms the genus has persisted in Europe since at least the Eocene, supporting biogeographic reconstructions indicating an ancient Euro-American distribution dating to the Late Cretaceous when land connections existed between North America and Europe.
Cyphophthalmi
Mite Harvestmen
Cyphophthalmi is a suborder of harvestmen (Opiliones) comprising six families grouped into three infraorders: Boreophthalmi, Scopulophthalmi, and Sternophthalmi. Adults range from 1 to 7 mm in length with relatively short legs compared to other harvestmen. The suborder is characterized by unique morphological features including elevated cone-shaped ozophores, a spermatopositor instead of a true penis in males, and a completely open gonopore lacking a genital operculum. Many species are eyeless and inhabit leaf litter or caves. Cyphophthalmi represents one of two major lineages of harvestmen, with the other lineage (Phalangida) containing Laniatores, Dyspnoi, and Eupnoi.
Diplopoda
millipedes
Millipedes (Diplopoda) are a class of myriapod arthropods characterized by having two pairs of jointed legs on most body segments, a result of segmental fusion during their evolutionary history over 400 million years ago. They are primarily detritivores that play critical roles in ecosystem nutrient cycling through decomposition of organic matter. The class contains approximately 12,000 described species across 16 extant orders, with body forms ranging from elongated cylindrical forms to short, pill-like species capable of conglobation (rolling into a defensive ball).
Gomphaeschna
Pygmy Darners
Gomphaeschna is a genus of small dragonflies commonly called pygmy darners, currently comprising two extant species native to eastern North America. It represents one of the most ancient surviving dragonfly genera known, with fossil records extending to the earliest Cretaceous (Berriasian) of Russia. The genus formerly had a much broader distribution across Eurasia and western North America, with multiple fossil species documented from the Paleocene through Miocene. Some taxonomic authorities recognize it as the sole genus of the distinct family Gomphaeschnidae due to its deep evolutionary origins.
Grylloblatta
ice crawler, rock crawler
Grylloblatta is a genus of ice-crawlers comprising 15 described species endemic to western North America. These insects represent an ancient lineage with obligate physiological dependence on stable near-freezing temperatures, with acute thermal tolerance between approximately -8.5°C and 10°C. The genus exhibits deep genetic subdivision and geographic structure, with diversification patterns tied to Pliocene-Pleistocene glacial cycles. Species occur in montane habitats, ice caves, glaciers, and subalpine forests, with some populations utilizing saproxylic habitats in beetle-killed trees.
Grylloblattodea
ice crawlers, rock crawlers
Grylloblattodea is a small order of extremophile insects commonly known as ice crawlers or rock crawlers. These wingless insects are adapted to cold environments and are found in montane habitats, caves, and subalpine forests across western North America and northeastern Asia. The order comprises approximately 25-30 described species in five extant genera, though significant undescribed diversity is suspected. Grylloblattids are predatory, feeding on other arthropods, and show remarkable cold tolerance. They are considered a relict lineage with ancient origins, closely related to Mantophasmatodea within the clade Xenonomia (order Notoptera).
Hexurella
dwarf funnel web spiders
Hexurella is a genus of dwarf funnel web spiders (Mygalomorphae, Hexurellidae) comprising some of the smallest mygalomorph spiders in the world. Adults measure 2.5–5 mm in body size. The genus represents a phylogenetically ancient, relictual lineage that diverged from other atypoids approximately 300 million years ago. As of 2026, the genus contains eight species, with four described in a 2023 taxonomic revision. Several species have highly restricted geographic ranges and may warrant conservation attention.
Ledrinae
Flat-headed Leafhoppers
Ledrinae is a subfamily of leafhoppers within Cicadellidae, comprising approximately 300 species across 38 genera in five tribes (Ledrini, Rubrini, Xerophloeini, Afrorubrini, and Hespenedrini). The group represents an early-branching, morphologically distinctive lineage considered one of the oldest within Cicadellidae. A major 2009 revision redefined the subfamily's boundaries, removing Stenocotini and Thymbrini to Tartessinae and synonymizing Petalocephalini with Ledrini. Diversity is concentrated in Australia, Africa, and the Oriental region, with China alone hosting over 180 species.
Lepismatidae
Typical Silverfishes
Lepismatidae is a family of primitive, wingless insects in the order Zygentoma, containing approximately 190-340 described species worldwide. The family includes the two most familiar domestic species: the silverfish (Lepisma saccharina) and the firebrat (Thermobia domestica). These ancient insects represent some of the earliest diverging lineages within Insecta, with origins dating back hundreds of millions of years. Members are characterized by elongated, flattened bodies covered in scales, three caudal filaments, and a complete absence of wings throughout their life cycle.
Limulidae
Horseshoe Crabs
Limulidae is a family of marine arthropods comprising four extant species: Limulus polyphemus in North America and three Indo-Pacific species (Tachypleus tridentatus, T. gigas, and Carcinoscorpius rotundicauda). These organisms possess a distinctive horseshoe-shaped prosoma, long telson, and compound eyes. Populations are declining globally, with T. tridentatus classified as Endangered by the IUCN. The family is notable for its ancient evolutionary lineage and biomedical importance due to hemolymph containing endotoxin-sensitive coagulation factors.
Opiliones
harvestmen, harvesters, daddy longlegs, granddaddy longlegs, shepherd spiders
Opiliones is an ancient order of arachnids comprising over 6,650 described species, with estimates suggesting more than 10,000 extant species worldwide. The order includes five suborders: Cyphophthalmi, Eupnoi, Dyspnoi, Laniatores, and Tetrophthalmi. Fossil evidence from 410 million-year-old Devonian deposits demonstrates that harvestmen have remained morphologically conservative since their early evolution. Despite superficial resemblance to spiders, Opiliones represent a distinct arachnid lineage with unique anatomical and behavioral characteristics.
arachnidharvestmandaddy-longlegsancient-lineageomnivorenocturnalgregariouscave-dwellingpaternal-carechemical-defenseautotomymodel-organismconservation-concernvenomlesstracheal-respirationdirect-copulationshort-range-endemictroglobiteaposematiccrypsismimicrythanatosisviscoelastic-adhesiveanurophagyvertebrate-predatorPetaluridae
petaltails, graybacks
Petaluridae is a relict family of dragonflies (Anisoptera) representing one of the most ancient lineages of extant dragonflies, with fossil records dating to the Jurassic period over 150 million years ago. The family comprises 11 extant species in five genera, divided into two major clades: a Laurasian clade (Tachopteryx, Tanypteryx) distributed in eastern and western North America and Japan, and a Gondwanan clade (Petalura, Phenes, Uropetala) found in Australia, New Zealand, and Chile. Petaltails are notable for their specialized larval habitats and extended development times, with most species persisting as independent lineages for 70–75 million years.
Staphylinidae
Rove beetles
Staphylinidae, the rove beetles, is the largest extant family of beetles with approximately 63,000 described species across thousands of genera. Members are distinguished by abbreviated elytra that expose most of the abdomen, giving them a characteristic elongated, flexible appearance. The family is ancient, with fossil records dating to the Triassic period approximately 200 million years ago. Ecological roles within the family are diverse, encompassing predation, fungivory, myrmecophily, and saprophagy.
Tanypteryx
Dark Petaltails, Black Petaltail (for T. hageni)
Tanypteryx is a small genus of petaltail dragonflies containing two species: T. hageni (black petaltail), found in the Pacific Northwest of North America, and T. pryeri, found in Japan. The genus represents an ancient lineage that diverged from its sister species approximately 70-73 million years ago, making it an evolutionary "living fossil." T. hageni is a habitat specialist with nymphs that occupy fen wetlands and dig burrows, an uncommon life history among dragonflies.
Tegeticula maculata
Chaparral yucca moth
Tegeticula maculata is a small moth in the family Prodoxidae, commonly known as the chaparral yucca moth. It is the sole pollinator of Hesperoyucca whipplei, forming an obligate mutualism in which the moth's larvae feed exclusively on developing seeds of this host plant. The species exhibits high genetic structure across its range with limited morphological divergence, suggesting ancient lineage sorting rather than recent speciation.
Tetrigidae
pygmy grasshoppers, groundhoppers, pygmy devils, grouse locusts
Tetrigidae is an ancient family of minute orthopterans with over 2,000 described species and a fossil record extending more than 230 million years. Members are characterized by an elongated pronotum that extends backward over the abdomen, often reaching the wing tips. The family exhibits exceptional morphological diversity, particularly in tropical regions where species display elaborate pronotal modifications including leaf mimicry, spines, and horns. Despite their ancient lineage and species richness, Tetrigidae remain among the most understudied orthopteran families.
Timarcha
bloody-nosed beetles
Timarcha is a genus of flightless leaf beetles comprising over 100 species across three subgenera, with a disjunct distribution spanning the Mediterranean region and western North America. The genus exhibits several unusual traits for Chrysomelidae, including complete apterism (winglessness), fused elytra, and archaic genital morphology. All species are uniformly black and herbivorous, with host plant associations concentrated in Rubiaceae and Plumbaginaceae. The most familiar species is T. tenebricosa, commonly known as the bloody-nosed beetle, named for its defensive reflex bleeding behavior.
Xiphosura
horseshoe crabs
Xiphosura is an order of marine chelicerate arthropods commonly known as horseshoe crabs. The group contains only four extant species, all within the family Limulidae. Xiphosurans first appeared in the fossil record approximately 480 million years ago and have retained a remarkably conserved body plan, earning them designation as living fossils. Recent phylogenomic studies have placed Xiphosura within Arachnida, often as the sister group to Ricinulei, though this classification remains under active revision. The order contains one extant suborder (Xiphosurida) and numerous extinct stem-genera.