Formica subsericea

Formica subsericea - "Silky Field Ant"

Formica subsericea is a large, dark brownish-black to black ant native to eastern North America. Workers measure 4.2-6.2mm and are covered with dense silvery appressed pubescence that gives them a silky sheen, particularly on the head, mesosoma, and first three gastral segments ^[1]. This species is highly adaptable and found in diverse habitats including woods, forest edges, fields, pastures, and even lawns. They construct low mound nests up to 1 meter in diameter, though they also nest under stones, logs, and leaf litter ^[2][1]. What makes F. subsericea particularly interesting is its role as both a host species for slave-making ants like Formica subintegra and Polyergus mexicanus, and as a predator that can dominate food resources in its territory ^[1][3].

Quick Summary

• Difficulty: Easy
• Origin & Habitat: Eastern North America, found from Nova Scotia south to Georgia, west to Manitoba, Michigan, Wisconsin, Iowa, Missouri, Oklahoma, Texas, New Mexico, and Arizona ^[1]. Inhabits woods, forest edges, semi-open areas, fields, pastures, and lawns ^[1][4].
• Colony Type: Monogyne (single queen) colonies with documented polygynous behavior in some populations. Colonies can be large, reaching up to 10,000 workers ^[1][5]. The polygynous nature allows colonies to persist for decades after queen death ^[6].
  • Colony: Optionally polygyne
  • Founding: Claustral
• Size & Growth:
  • Queen: Larger than workers, queens are chunky with substantial fat reserves for claustral founding ^[1].
  • Worker: 4.2-6.2mm ^[1].
  • Colony: Up to 10,000 workers ^[1][7].
  • Growth: Moderate, first workers (nanitics) are smaller and weaker than subsequent brood ^[6].
  • Development: 6-8 weeks estimated based on typical Formica development patterns. (First batch of workers are smaller and weaker, focusing on feeding the queen before expanding the nest ^[6].)
• Antkeeping:
  • Temperature: Keep nest area at 20-24°C. Maximum thermal tolerance is 40°C ^[7]. They tolerate a range from cool forest conditions up to warm temperatures. A heating cable on one side creates a gradient for them to regulate their temperature ^[1].
  • Humidity: Moderate humidity, they nest in soil and prefer areas with some moisture. Keep substrate consistently moist but not waterlogged. They do well in naturalistic setups with damp soil ^[1][2].
  • Diapause: Yes, as a temperate species they require a winter rest period. In their northern range, colonies experience cold winters and are adapted to seasonal temperature changes ^[1].
  • Nesting: Large, naturalistic setups work best. They build extensive nests with deep tunnels (0.7m+ in the wild) and prefer soil-based formicaria or Y-tong nests with room for colony expansion. They construct low mound nests in nature but will also use logs and stumps ^[1][6].
• Behavior: Workers are fast-moving and most active during midday ^[1]. They are generalist foragers that hunt insects, collect honeydew from aphids, and gather seeds. They can be aggressive when defending their nest and use formic acid spray as a defense mechanism ^[8]. They are strictly diurnal, foraging during daylight hours ^[9]. Escape prevention is straightforward, they are large ants that cannot squeeze through standard barrier gaps. They are known to dominate food resources and can displace smaller ant species at baits ^[10].
• Common Issues: colonies may fail if kept too dry, they need moist substrate for brood development, large colony size means they need significant space as they grow, plan for expansion, they can be targets of parasitic ants if kept near other Formica species, overheating can be fatal despite their high thermal tolerance, provide temperature gradient, wild-caught colonies may have parasites that need treatment

Housing and Nest Setup

Formica subsericea needs space. In the wild, their nests can extend 0.7m to over 1m deep with extensive tunnel networks ^[6]. For captive colonies, use a large naturalistic formicarium or Y-tong setup with deep soil chambers. They prefer soil-based substrates where they can dig and construct galleries. A test tube setup works for founding colonies, but be prepared to move them to a larger setup once the colony reaches 20-30 workers. They construct distinctive v- or y-shaped chambers at nest entrances and expand tunnels downward and outward as the colony grows ^[6]. Provide a water tube and keep the substrate consistently moist but not soggy.

Feeding and Diet

These ants are generalist feeders. In nature, they forage for insects, collect honeydew from aphids, and gather seeds ^[1]. They are known to tend at least 10 aphid species including Aphis coreopsidis, Aulacorthum solani, Cinara atlantica, and Rhopalosiphum nymphaeae ^[11]. In captivity, offer protein sources like mealworms, crickets, or other small insects 2-3 times per week. Provide sugar water, honey, or diluted maple syrup as a constant carbohydrate source. They will also accept myrmecochorous seeds (seeds with elaiosomes) which they transport an average of 12 meters in the wild ^[12]. Fresh killed insects are preferred over freeze-dried options.

Temperature and Seasonal Care

Keep the nest area at 20-24°C with a temperature gradient. These ants have a maximum thermal tolerance of 40°C ^[7], which is quite high, but they prefer moderate temperatures matching their forest-edge habitat. A heating cable on one side of the nest allows workers to regulate their temperature by moving between warmer and cooler areas. During winter, they require a diapause period. Reduce temperature to 5-10°C for 2-3 months, mimicking winter conditions in their native range. This rest period is essential for colony health and triggering reproductive development the following spring. Males and females develop from July to late August, with nuptial flights occurring mid-July through early September ^[1].

Behavior and Defense

Workers are fast runners and strictly diurnal, they forage during daylight hours and rest at night ^[9][1]. When threatened, they use formic acid spray as their primary defense ^[8]. They are aggressive defenders of their territory and can dominate other ant species at food sources. In direct encounters, they often outcompete smaller ants like Aphaenogaster species ^[13]. However, they are known to flee from slave-making ants like Formica sanguinea rather than fight, demonstrating what Forel described as 'cowardice', an instinctive response where they abandon their nest to escape capture ^[3]. This is an interesting behavioral trait to observe if you keep multiple Formica species.

Colony Growth and Development

New colonies start with a single claustral queen who seals herself in a chamber and raises the first brood alone on stored fat reserves ^[6]. The first workers (nanitics) are smaller and weaker than subsequent workers, and their primary task is feeding the queen before expanding the nest. As the colony grows, workers dig more tunnels and chambers, with gallery networks becoming more extensive and interconnected ^[6]. Colonies can live for decades in the wild due to their polygynous capability, multiple queens allow the colony to survive if one dies ^[6]. Maximum colony size is around 10,000 workers, which typically takes several years to reach under good care.

Common Ant Associates

In the ant world, F. subsericea plays an interesting role as both host and competitor. Several parasitic ant species target them: Formica subintegra, Polyergus lucidus, Formica dakotensis, F. difficilis, F. aserva, F. pergandei, and F. rubicunda all use F. subsericea as hosts ^[1]. Slave-making ants raid their colonies and steal pupae to raise as workers. They also host the parasitic fly Microdon megalogaster, whose larvae and pupae develop in their nests ^[14]. Despite these parasitic relationships, F. subsericea remains common and widespread, likely due to their large colony size and adaptability.

Frequently Asked Questions

References