Sexual-dimorphism
Guides
Xenos
twisted-wing parasites
Xenos is a genus of twisted-wing parasites in the order Strepsiptera. These insects are obligate endoparasites of other insects, with larvae entering hosts through joints or sutures. Adult males are free-flying and short-lived, while neotenic females remain permanently within host abdomens. The genus includes species such as Xenos peckii, which parasitizes wasps including Polistes fuscatus.
Xenos peckii
Xenos peckii is a highly specialized endoparasitic insect in the order Strepsiptera, commonly known as twisted-wing parasites. It is an obligate parasite of paper wasps, specifically Polistes fuscatus, with development occurring entirely within the host's abdominal cavity. The species exhibits extreme sexual dimorphism: males are free-flying adults with reduced wings and unusual eyes containing green- and UV-sensitive photoreceptors, while females are neotenic, lacking wings, legs, and eyes, and remain permanently embedded within the host. Males locate females through a species-specific sex pheromone, (3R,5S,9R,7E,11E)-3,5,9,11-tetramethyl-7,11-tridecadienal, which females actively release by inflating and extruding their cephalothorax through the host's cuticle. The species has been documented across temperate North America and possesses unique cellular mechanisms for meiotic spindle formation that have been studied ultrastructurally.
Xylocopa sonorina
Valley Carpenter Bee, Hawaiian Carpenter Bee
Xylocopa sonorina is one of the largest bees in California and Hawaii, reaching approximately 25 mm in length. The species exhibits strong sexual dimorphism: females are entirely black, while males are golden-brown with distinctive green eyes. Native to the southwestern United States and adjacent Mexico, it has been introduced to the Hawaiian Islands (since before 1874), French Polynesia, the Samoan Islands, and other Pacific archipelagoes through human-mediated transport of nesting wood. DNA analysis confirmed in 2020 that X. varipuncta is a synonym of X. sonorina. The species is a significant pollinator, including commercial pollination of passion fruit in Hawaii, though its wood-nesting behavior can cause structural damage.
Xylosandrus germanus
black stem borer, alnus ambrosia beetle, black timber bark beetle
Xylosandrus germanus is a tiny ambrosia beetle native to eastern Asia that has become a significant invasive pest in Europe and North America. Females, which are flight-capable and substantially larger than the flightless males, excavate galleries in stressed or recently dead woody plants to cultivate fungal gardens. The species exhibits a quasisocial structure with foundress females performing distinct behavioral roles that shift from gallery construction and brood care to entrance-blocking as the colony matures. Its rapid spread—tens of kilometers per year in some regions—is facilitated by climate change, global timber trade, and an unusual reproductive system where single foundresses can establish populations through sib-mating.
Xysticus
Ground Crab Spiders
Xysticus is a large genus of approximately 275–300 species of ground crab spiders in the family Thomisidae. These spiders are ambush predators that do not build webs, instead hunting near the ground by seizing prey with their enlarged anterior legs. The genus exhibits strong sexual dimorphism, with females typically reaching 10 mm in body length while males are roughly half that size. Species identification requires microscopic examination of genitalia due to the morphological similarity among members of the genus.
Xysticus elegans
elegant crab spider
Xysticus elegans, commonly known as the elegant crab spider, is a medium-sized crab spider in the family Thomisidae. The species exhibits pronounced sexual dimorphism in body size, with females approximately twice as large as males. It is distributed across northern North America including the United States, Canada, and Alaska. The spider is characterized by distinctive coloration including a brown cephalothorax with lighter areas and white-outlined brown spots on the abdomen.
Zarhipis
glowworm beetles
Zarhipis is a genus of glowworm beetles in the family Phengodidae, containing three recognized species restricted to western North America. Members of this genus exhibit sexual dimorphism, with females being larviform and bioluminescent while males are winged and non-luminous. The genus has been subject to population genetic studies, particularly for Zarhipis integripennis, revealing significant geographic structure and sex-biased dispersal patterns.
Zarhipis integripennis
western banded glowworm
Zarhipis integripennis, the western banded glowworm, is a glowworm beetle in the family Phengodidae. Males are winged and capable of flight, while females are larviform and flightless, creating strongly asymmetrical dispersal abilities between sexes. This sexual dimorphism has significant consequences for population genetic structure and gene flow patterns.
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.
Zethus
mason wasps, potter wasps
Zethus is the largest genus in the subfamily Eumeninae (potter and mason wasps), containing over 250 species. The genus is predominantly Neotropical in distribution, with three recognized subgenera: Zethus (Zethus), Zethus (Zethusculus), and Zethus (Zethoides). Species are solitary and construct nests using diverse materials including mud, sand, vegetable matter, and insect parts. Many species are poorly known, with numerous taxa described from only one sex.
Zygoballus sexpunctatus
Zygoballus sexpunctatus is a small jumping spider (3–4.5 mm) found in grassy habitats of the southeastern United States. Males possess enlarged chelicerae and front femora, and exhibit elaborate courtship and agonistic displays involving leg-raising and abdominal vibration. The species name refers to the six abdominal spots typically present in males, though these may be reduced or absent. First described by Hentz in 1845, it was later transferred to the genus Zygoballus by the Peckhams in 1888.