California-endemic
Guides
Trichinorhipis knulli
Knull's Metallic Wood-boring Beetle
Trichinorhipis knulli is a minute jewel beetle (family Buprestidae) endemic to southern California, where it occurs in Riverside and Imperial Counties. It is the sole member of its monotypic genus, distinguished from related genera by its entire elytra covering the full abdomen and broadly rounded pronotum lacking lateral margins. Males exhibit highly modified flabellate antennae with expanded lamellae bearing numerous olfactory sensillae, an adaptation for detecting female sex pheromones. The species is rarely encountered in the field; most specimens have been reared from dead branches of jojoba (Simmondsia chinensis). At 3.6 mm, it is among the smallest buprestids.
Tricholathys monterea
Tricholathys monterea is a small spider in the family Dictynidae, first described from specimens collected in California in 1958. The genus Tricholathys comprises North American cribellate spiders that construct irregular, tangled webs. This species is poorly documented in scientific literature, with minimal published information on its biology or ecology.
Tricholepidion
Tricholepidion
Tricholepidion is a genus of wingless insects in the order Zygentoma, containing a single described species, T. gertschi. It is endemic to the northern coast of California and represents the sole living member of the family Lepidotrichidae, with fossil relatives known from Eocene amber. Its taxonomic position is uncertain; molecular studies have sometimes recovered it as more distantly related to Pterygota than other Zygentoma, which would render Zygentoma paraphyletic. The genus is considered a 'living fossil' due to its isolated phylogenetic position and the extinction of all other family members.
Trimerotropis leucophaea
Inyo Blue-wing Grasshopper
Trimerotropis leucophaea, described by Rentz & Weissman in 1984, is a band-winged grasshopper in the family Acrididae. The species is known from California and is part of the North American grasshopper fauna. As a member of the genus Trimerotropis, it belongs to a group known for cryptic coloration and banded wings. Very few observations of this species have been recorded.
Trirhabda flavolimbata
Coyote Brush Leaf Beetle
Trirhabda flavolimbata, commonly called the coyote brush leaf beetle, is a skeletonizing leaf beetle in the family Chrysomelidae. It is restricted to California where it inhabits coastal scrublands and chaparral. Both larvae and adults are metallic green and sequester toxins from their host plants, rendering them unpalatable to predators. The species has a single annual brood with a distinctive life cycle involving extended egg diapause.
Twiningia bicolor
Bicolored leafhopper
Twiningia bicolor is a leafhopper species in the family Cicadellidae, first described by Ball in 1909. The specific epithet "bicolor" refers to its two-colored appearance. Like other members of the tribe Platymetopiini, it belongs to the diverse subfamily Deltocephalinae, one of the largest groups of leafhoppers. The genus Twiningia is classified within the Membracoidea superfamily, a major radiation of sap-feeding insects.
Twiningia pellucida
Twiningia pellucida is a species of leafhopper in the family Cicadellidae, first described by Ball in 1909. It is classified within the subfamily Deltocephalinae and tribe Platymetopiini. The species is known from California, with limited observational records available.
Udea vacunalis
Udea vacunalis is a small crambid moth described by Augustus Radcliffe Grote in 1881. It is known only from California, with adults active during summer months. The species is characterized by pale, nearly unmarked wings with distinctive marginal dotting on the hindwings.
Uroctonites montereus
Uroctonites montereus is a scorpion species in the family Vaejovidae, described from Monterey County, California. It belongs to a genus of small to medium-sized scorpions found in western North America. The species is part of a taxonomic group that has undergone significant revision, with Uroctonites species historically classified under different genera.
Uroctonus mordax
California forest scorpion, western forest scorpion
Uroctonus mordax is a small scorpion species in the family Vaejovidae, endemic to the coastal forests of California and extending into western Oregon and southern Washington. It is strongly associated with Redwood Forests and Oak Woodlands, where it occupies a foundational ecological role. The species exhibits distinctive physical traits including a squat body, slender tail, and sexually dimorphic coloration. It is notable for its mild venom and reclusive, nocturnal behavior.
Xanthothrix
Xanthothrix is a genus of owlet moths in the family Noctuidae, erected by Henry Edwards in 1878. The genus contains four described species distributed across western North America and the eastern Mediterranean region. Two species are endemic to California, with one restricted to the Mojave Desert. The genus belongs to the subfamily Stiriinae, a group of generally small, often boldly patterned noctuid moths.
Xenicopoda
Xenicopoda is a genus of rove beetles (family Staphylinidae) in the tribe Anthophagini. It is monotypic, containing only the single species Xenicopoda helenae, which is known from California. The genus was established by Moore and Legner in 1971.
Xenicopoda helenae
Xenicopoda helenae is a species of rove beetle (Staphylinidae) described from California in 1971. It belongs to the subfamily Omaliinae, a group of rove beetles often associated with decaying plant matter and fungal habitats. The species is known from limited collection records in California.
Xenolechia ceanothiella
Xenolechia ceanothiella is a gelechiid moth native to California. The larvae are leaf miners that feed exclusively on Ceanothus divaricatus, creating distinctive mines that begin linear and expand into blotches. Pupation occurs in a silk cocoon spun between two leaves. The species is known from limited records and appears to have a restricted distribution within its host plant's range.
Xorides californicus
Xorides californicus is a species of ichneumon wasp in the subfamily Poemeniinae. It is a parasitoid wasp known to attack wood-boring beetle larvae. The species was described by Cresson in 1879 and is native to western North America, particularly California. Like other members of its genus, it possesses a long ovipositor used to reach beetle grubs tunneling in wood.
Xystocheir
Xystocheir is a genus of flat-backed millipedes in the family Xystodesmidae, endemic to California. The genus comprises nine species distributed in the Coast Ranges and Sierra Nevada. Members of this genus are notable for producing cyanide as a chemical defense against predators. Xystocheir dissecta, a species within this genus, has been documented to fluoresce under ultraviolet light.
Xystocheir dissecta
Xystocheir dissecta is a flat-backed millipede in the family Xystodesmidae. It is found along the coast of Northern California, particularly in and around the San Francisco Bay Area. The species is notable for its chemical defense system, producing hydrogen cyanide gas when threatened. Three subspecies are recognized: X. d. dissecta, X. d. microrama, and X. d. taibona.
Xystocheir dissecta taibona
Xystocheir dissecta taibona is a subspecies of flat-backed millipede in the family Xystodesmidae. It is a synonym of Xystocheir taibona and is known from California. Like other members of its genus, it produces cyanide as a chemical defense against predators. The subspecies is documented as prey for the specialized carabid beetle Promecognathus.
Zerene eurydice
California dogface butterfly, flying pansy, dog head butterfly
Zerene eurydice, commonly known as the California dogface butterfly, is a pierid butterfly endemic to California and designated as the state's official insect since 1972. The species exhibits pronounced sexual dimorphism: males display distinctive black and yellow-orange wing patterns resembling a dog's head silhouette, while females are predominantly yellow with black forewing markings. The butterfly is closely associated with its larval host plants, false indigo species (Amorpha californica and A. fruticosa), and is most abundant at the Shutamul Bear River Preserve near Auburn. Despite its cultural prominence, the species remains rarely encountered in the wild due to its fast, high-flying behavior and specific habitat requirements.