Formica prociliata
The Golden Shiny Ant
Formica prociliata is a beautifully colored, active species from the Midwest. We consider this species Endangered, largely due to the large areas they need to maintain a population. We recommend urgent focus on habitat restoration for them, and, therefore, their host species, Formica dolosa (LC).
Species Profile
Formica prociliata is a species largely limited to glaciated, remnant dry-mesic prairies (or sometimes savannas) in the Midwest. Today, it is largely restricted to sandy or bluff prairies/savannas. It has its strongest populations in the Driftless area, largely in Wisconsin, but also has a documented, notable, but underresearched population in northern Michigan. This species is largely threatened by habitat loss, which is of special concern to this species because it forms large colonies (10s of thousands) that require a large amount of resources. Many remnant prairies in WI may have a population, but this population often consists of very few colonies, sometimes only a single colony containing multiple queens. This means inbreeding and eventual death of the population are inevitable without intervention.
Life History
Formica prociliata is a social parasite. This means that to begin a new colony, the queens infiltrate existing queenright colonies of Formica dolosa and kill the queen. Many times, they fail and are killed. This means that to maintain a healthy population, you need a rather large population of the host species. This tends to require a decent amount of healthy habitat in one area.
Once a queen has infiltrated a colony, she uses the host workers to grow her own first generation. As the host workers die out, the colony is slowly replaced by Formica prociliata workers and grows much larger than the host colony could have. While Formica dolosa colonies rarely exceed 1,000 workers, Formica prociliata can have colonies with more than ten times that number.
Colonies are often polydymous, meaning they have multiple nests. Workers will often trail between these nests and these nests are not hostile to one another. Nests are typically a slightly raised, very loosely thatched (depending on the surrounding materials) mound. In some cases, nests can be hard to spot, especially during peak growth. It's not uncommon for colonies to nest under large rocks, and in some cases mound some thatch around the edges.
A large colony is living beneath this rock. Thatch is surrounding the rock.
These ants are omnivorous. They collect nectar from plants (pollinating them, often), as well as honeydew excreted by sap-sucking insects (aphids, coccids, some leafhoppers, etc). They're also avid scavengers and hunters. They will often hunt very small insects, and when a larger insect (or even small animal) dies, they'll often eat from those too. Grasshoppers are inevitably a regular food source during later parts of the summer.
In small populations, it seems that queens are somewhat prone to rejoining colonies instead of infiltrating their host. While this gives them a much better chance of short-term survival, it doesn't help their long-term cause.
Habitat
While a small remnant prairie could hold one colony or even a handful of colonies, these ants are living on borrowed time. The populations are often isolated, living miles apart. This means inbreeding is nearly inevitable.
One of the best examples of a large, seemingly healthy population for this species is located at the Spring Green Preserve in Spring Green, Wisconsin. This preserve is managed by the Nature Conservancy and is one of the largest, healthiest sand prairies in the midwest. It has about 200 acres of quality prairie/oak savanna, and additional prairie around that which was restored. Though part of Spring Green is remnant, part of it is also restored, and the Formica prociliata have been doing well and moving into the restoration areas. This is a great sign!
Their habitat can vary. It seems they largely prefer open, dry-mesic prairies, but will do well in mostly open savannas (oak, sometimes pine, like in Michigan) as well. They don't seem to do well in overcrowded, fertile prairies. Goldenrod prairies don't seem to cater to them. These ants cannot survive long in closed canopy forest. It's important to focus especially on forb diversity with this species. They seem to do well with milkweed (which is known to host plenty of aphids). One population in Wisconsin, on a dry prairie hill, was notable in that almost every Asclepias viridiflora plant was foraged by at least some workers of Formica prociliata.
Formica prociliata queen surrounded by her workers
Range
Though originally described from Catawba Island, Ohio, searches in the area for the type population have had no avail. Indeed, the nearest records are the northern Michigan population. No Formica prociliata have been found in Ohio for a long time.
In modern times, the only known population clusters are: Wisconsin (mostly the Driftless Area, but the central sand plains and some prairie remnants near Madison hold small populations), Michigan (northern part of the state, near Grayling, Tawas City, and Harrison).
There have been a very small amount of records in northern Missouri (one photographed near Maysville, MO, and one report right beneath the Iowa border). This population cluster, though likely underdocumented, is probably rather small.
Recommended Action
We recommend working with landowners, state officials, and conservation programs to expand upon remnant prairies/savannas in the native range of Formica prociliata. Efforts are likely best concentrated here.
We estimate that for a viable long-term population, there should be at least 100 acres of healthy habitat, ideally more than that. To keep a population alive in the short term, there should be at least 5-20 acres of healthy habitat.
Healthy habitat is, in many cases, an open dry-mesic prairie or savanna that is burned frequently. It's good to alternate burn years and times of years to allow forb diversity, but it's also essential to ensure there's open space between plants, as this is a characteristic seen in many of their best habitats.
Asclepias viridiflora is a dry upland species of Milkweed which tends to prefer high-light, dry conditions. It has been a notably attractive plant to Formica prociliata, and it's recommended that any attempted restorations of dry-mesic prairie that want to keep this species in mind seed the area to some small degree with A. viridiflora. Though it is true that efforts are best concentrated in adjacent or very near to remnant prairies (especially already occupied by Formica prociliata), restorations should not be ruled out.
We recommend that some of the isolated populations have small pieces of colonies taken, and, though easier said than done, transplanted to other population areas for better genetic diversity. Eventually, it is our hope that large restored plots can be 'seeded' with Formica prociliata.
Their host, Formica dolosa, is a fairly generalist and hardy species, often with (stunted yet viable) populations in parks and neighborhoods. They excel, however, in very open, diverse, dry-mesic prairies. In any very recent restoration, it's recommended that Formica dolosa populations are monitored and catered to for at least 5-10 years prior to introduction of Formica prociliata. Areas with established F. dolosa populations should be seeded as soon as the habitat is in good shape.
Nuptial flights seem to occur in late June and early July. Keep preserves clear of large disturbance during this period, as queens may be abundant, attempting to infiltrate host colonies.
An F. prociliata mound after a recent burn at Spring Green Preserve, WI
A small piece of Formica prociliata habitat.