Formica subsericea (The Silky Field Ant)
Introduction
Formica subsericea, commonly known as the Silky Field Ant, is one of the most elegant and widely recognized field ants in North America. Its common name is derived from the fine, dense, silvery hairs that cover its jet-black body, giving it a beautiful matte finish that shimmers like silk under the right light. These ants are quintessential inhabitants of open fields, forest edges, and meadows, where they are known for their incredible speed, alertness, and active, daytime foraging. They are among the largest and most robust of the North American "black ants."
For ant keepers, Formica subsericea is a "high-energy" species that provides a fantastic observation experience. They are much more active and reactive than many other common black ants. Known for their keen eyesight and "twitchy" movements, they are constantly on the lookout for food or threats. They are also famous for their role in the complex world of ant social parasitism, often being the preferred hosts for various slave-making ant species. Keeping a colony of Silky Field Ants is a rewarding way to experience the dynamic life of the North American prairie and woodland edge.
Taxonomy and Distribution
Formica subsericea belongs to the subfamily Formicinae and the subgenus Serviformica. This subgenus is known for being relatively peaceful and for acting as "hosts" to various social parasites like Formica sanguinea or Formica aserva. F. subsericea is often confused with its European relative Formica fusca, but it is generally larger and has a more pronounced "silky" sheen due to its unique pubescence.
Their distribution is vast, covering much of North America from Southern Canada through the United States to Northern Mexico. They are incredibly adaptable and can be found in a wide variety of habitats, including open grasslands, deciduous forest clearings, meadows, and even suburban lawns. They prefer sunny locations where they can take advantage of the sun's warmth to heat their nests, which are typically located in the soil, often under stones or at the base of plants.
Physical Characteristics
Formica subsericea is a monomorphic species, with workers typically ranging from 6mm to 8mm in length. The queen is a substantial and impressive figure, measuring around 10-12mm. They have a classic Formica build: long legs for rapid movement, a large and robust thorax, and a relatively large head with well-developed eyes. Their coloration is a deep, uniform jet-black, but it is the "silky" pubescence that truly sets them apart, giving their body a soft, velvety texture.
Their eyes are among the largest and most developed of any common North American ant, providing them with excellent visual acuity. This allows them to detect movement from several inches away and to navigate using visual landmarks. They possess a "formic acid" gland at the tip of their gaster, which they use both for defense and to subdue small prey. Their entire anatomy is built for speed, agility, and visual alertness.
Colony Behavior and Social Structure
Colonies of Formica subsericea are typically monogynous (one queen), though some populations have been reported to exhibit polygyny (multiple queens). A mature colony can grow to include several thousand workers. They are highly organized and maintain very clean, efficient nests. Socially, they are quite cooperative, with a clear division of labor that changes as workers age: younger workers stay in the nest to care for the brood, while older workers become the colony's foragers and scouts.
They are not as aggressive as some other Formica species but are very alert. When a threat is detected, they will run in rapid, erratic patterns to confuse the predator and will use their formic acid for defense if necessary. In the outworld, they are famous for their "tandem running" and visual navigation. Watching them coordinate their foraging efforts and communicate through rapid antennal contact is one of the most engaging aspects of keeping this species.
Diet and Foraging
Formica subsericea is a generalist omnivore with a very high metabolism. They require a consistent and diverse diet to support their active lifestyle. They are efficient hunters and will take down small insects like fruit flies, gnats, and small crickets. They are also opportunistic scavengers, quickly locating and dismantling larger dead insects. In captivity, providing a regular supply of high-quality protein is essential for the growth of the brood and the health of the queen.
In addition to protein, they have a strong "sweet tooth." In the wild, they are frequent visitors to aphids and other honeydew-producing insects, which they milk for their sugary secretions. In a home setup, they must be provided with sugar water, honey, or specialized ant syrups. They are most active during the warmest parts of the day, reflecting their preference for solar-heated environments. Their foraging trails in the outworld are always busy and provide endless opportunities for observation.
Life Cycle and Reproduction
The development from egg to adult in Formica subsericea is relatively fast, typically taking about 6 to 8 weeks. Like all Formicinae, they pupate within silk cocoons. The workers are very active in the care of these cocoons, often moving them to the warmest and most humid parts of the nest to ensure they develop properly. The emergence of a new, pale "callow" worker is a common and fascinating sight in a healthy colony.
Nuptial flights take place in the summer, usually between June and August, on warm, calm afternoons following a rain. Thousands of winged queens and males take to the air to mate. After mating, the queen searches for a suitable spot in the soil to start her new colony. She is a claustral founder, meaning she doesn't eat until her first generation of workers has reached adulthood. In captivity, these queens are robust and have a high success rate if provided with a quiet, dark environment.
Environmental Requirements
To keep Formica subsericea thriving, you must provide a warm and bright environment. They require a temperature gradient in the nest, with a warm area around 24-26°C (75-79°F). Humidity should be kept at a moderate level, around 50-60%. Because they are visual foragers, they appreciate a well-lit outworld, though the nest area should be kept dark and stable. They are sensitive to vibrations, so the habitat should be placed in a quiet location.
Hibernation is a vital requirement for this temperate North American species. From November to March, the colony should be kept in a cool area (around 5-10°C). This period of diapause is essential for the queen's fertility and the colony's overall longevity. During hibernation, they require very little care, only needing occasional checks to ensure they have enough moisture to prevent dehydration.
Keeping Formica subsericea as Pets
Formica subsericea is an excellent choice for any ant keeper who wants a species that is active, beautiful, and full of personality. Their "silky" appearance and high-speed behavior make them a standout in any collection. They are hardy and adaptable, making them a great choice for both beginners and more experienced keepers. Whether they are hunting in the outworld or carefully tending to their cocoons in the nest, the Silky Field Ant provides a constant and fascinating window into the natural world.
Recommended Habitats
For an active and fast species like F. subsericea, a habitat that allows for rapid movement and easy observation is key. We recommend the following ANT SHACK products:
- All-in-One Desktop Ant Habitat - This is an ideal setup for F. subsericea. The integrated outworld provides plenty of space for their high-speed foraging, and the secure acrylic nest offers crystal-clear viewing of their complex social interactions.
- Natural Ant Habitat Kit - Large - For those who want to provide a more realistic field environment. The large volume allows you to use soil and stones to create a naturalistic nest site, which these ants will quickly colonize and organize.
- Ant Habitat “Paris“ - For larger, more established colonies. The "Paris" model's horizontal layout is perfect for watching the "tandem running" and visual navigation that this species is known for, while its high-quality construction ensures a safe and secure home.