Castianeira is the only genus from the family Corinnidae that has been found in Minnesota. Many of these are mimics of hymenopterans (not just ants but also velvet ants). Their bodies are longer than wide, often with white or orange hairs. These hairs may be dense or diffuse on the carapace but often form distinct bands on the abdomen. Males possess a sclerite (think armored plate) that covers much of the dorsal surface of the abdomen; this feature is often indistinct. In females, it is much smaller in size and positioned toward the anterior. The legs are thin and often have white longitudinal stripes. These spiders are active hunters and move very quickly across the ground. They can sometimes be found under rocks, logs or other debris in appropriate habitats.

Members of this genus are often confused with spiders in the genus Sergiolus or Micaria in the family Gnaphosidae; these genera can also be brightly colored, boldly patterned and ant-like. Confusion can also occur within members of the same species of Castianeira. Individuals may vary in their base color as well as the banded pattern of hairs on the abdomen (though sometimes this is due to physical wear and not genetics). Variation within species is described more thoroughly below.

C. amoena goes by the common name of Orange Ant-Mimic Sac Spider on iNaturalist and is the most distinctive member of this genus in Minnesota. It is bright orange over much of its body with black bands on the abdomen. Its overall appearance is designed to look like a female velvet ant which is not an ant at all but rather a brightly colored ant-like wasp. The bright, contrasting pattern is designed to warn unsuspecting people that they pack quite a sting if you choose to pick one up. Looking like such an insect may provide some protection to the spider. This is a southern species that reaches the northern limit of its distribution in Minnesota. It is typically found in non-forested areas and prefers areas with rock outcroppings (Reiskind, 1969). This species is only known from Rock County in the southwestern corner of the state. Example of this species: https://bugguide.net/node/view/491173/bgimage ; https://bugguide.net/node/view/161378/bgimage.

C. cingulata or Two-banded Ant-Mimic Sac Spider has two distinct morphs (both found in Minnesota). As the common name indicates, all morphs have two pale bands on the anterior half of an abdomen that is sometimes larger toward the posterior. The femurs have dark stripes (sometimes bordered with white) on the dorsal surface as well as the femurs' sides. The "black morph" resembles a Black Carpenter Ant (Camponotus pennsylvanicus); the body is dark brown to black overall with diffuse white scales on the carapace. The carapace of the "bicolored morph" is brown toward the posterior but much darker (black) at the anterior; its abdomen is generally dark brown to black. I think this morph resembles the New York Carpenter Ant (C. novaeboracensis). This species is more common in forested ecosystems where it actively hunts for prey in the leaf litter (Reiskind, 1969). It is currently known from 17 Minnesota counties across the state. Black Morph male: https://bugguide.net/node/view/327240/bgimage Bicolored Morph female: https://bugguide.net/node/view/1371351/bgimage.

C. descripta on iNaturalist is assigned the common name of Red-spotted Ant-Mimic Sac Spider (with two other species). Perhaps a better name for it would be the Variable Red-spotted Ant-Mimic Sac Spider. Reiskind (1969) indicates that the size of the red spot on the dorsal surface of the abdomen typically gets larger as you move south and west across this species' range. The examples found by iNaturalist observers suggest that in Minnesota, males typically have a red spot that covers much of the abdomen but the size of the red spot is highly variable in females (and not related to geography). Females also show variable amounts of white hairs on their abdomen, sometimes none and other times forming transverse bands or an alternating black and white pattern. This species can be found in prairies as well as woodlands (Reiskind, 1969) which may well explain its broad distribution. It is currently known from 25 counties across the state. One other note: In Minnesota, a black spider with red on the abdomen is much more likely to be this species than a Black Widow, especially away from the southeastern Mississippi River bluff counties where widows can be rarely found.. Various forms of this species: https://www.inaturalist.org/observations/175434003 ; https://www.inaturalist.org/observations/168721899 ; https://www.inaturalist.org/observations/5211141 ; https://www.inaturalist.org/observations/130564264.

C. longipalpa or Long-palped Ant-Mimic Sac Spider. The carapace can be brown to black with diffuse to dense white hairs. The abdomen is typically darker brown to black with transverse bands of white hairs that may not reach the lateral edges and may be conjoined at the median. Their legs may have white rings and longitudinal stripes. This species can be found in prairies and well as woodlands and has the broadest distribution for any member of the genus in North America (Reiskind, 1969). In Minnesota it is known from nine counties but likely occurs statewide. Some examples of this species: https://www.inaturalist.org/observations/132485817 ; https://www.inaturalist.org/observations/131886556 ; https://www.inaturalist.org/observations/5211156.

C. trilineata has not been assigned a common name on iNaturalist and is hypothetical in its occurrence in Minnesota. It is known from Wisconsin (Reiskind, 1969). The carapace is orange-brown and shiny and the abdomen is red-brown with two bands of white hairs on the anterior half of the abdomen and a shorter band toward the posterior. Guarisco (2021) indicates that this species is similar to C. cingulata but it lacks the dark longitudinal stripes on the femurs and its legs get paler distally. A research grade example from iNaturalist: https://www.inaturalist.org/observations/144861451.

SOURCES
Guarisco, Hank. 2021. Castianeira of Kansas. Newsletter of the American Arachnological Society. Number 87.

Reiskind, Jonathan. 1969. The spider subfamily Castianeirinae of North and Central America (Araneae, Clubionidae). Bulletin of the Museum of Comparative Zoology, 138:286-325.