Formica yessensis

Formica yessensis

Formica yessensis is a large red wood ant native to East Asia, found throughout Japan (especially Hokkaido and northern Honshu), Korea, northeastern China, and the Russian Far East. Workers measure 4.5-7mm with a reddish-brown body, darker head and mesosoma, and a black gaster. This species is famous for forming one of the largest supercolonies ever documented, the Ishikari supercolony on Hokkaido spans 2.7 km² with approximately 45,000 interconnected nests containing over 300 million workers and one million queens ^[1][2]. Unlike typical mound-building wood ants, F. yessensis builds loose thatch mounds from dead grass and conifer needles, with many nests being nearly moundless in their coastal sandy grassland habitat ^[3]. The species occupies an ecological niche similar to Formica pratensis in Europe, relatively small colony sizes, polygynous, poor mound formation, and a preference for open areas and forest edges ^[4].

Quick Summary

• Difficulty: Medium
• Origin & Habitat: Japan (Hokkaido, northern Honshu), Korea, northeastern China, Russian Far East (Siberia, Primorye). In Japan, found in coastal sandy grassland at Ishikari Bay, Hokkaido, and mountainous areas on Honshu. Prefers open sunny locations at forest edges, typically nesting under root systems of grasses like Miscanthus sinensis (eulalia) ^[5][2].
• Colony Type: Highly polygynous (multiple queens per nest) and polydomous (multiple connected nests). Colonies contain 1-213 queens per nest, averaging 24. Worker population ranges from 260 to 51,000 per nest, averaging 6,800 ^[6]. Queens are not particularly large compared to workers, suggesting possible temporary social parasitism similar to Formica fukaii ^[2]. The species forms massive supercolonies through budding, new nests are established by groups of workers departing from existing nests, with queens later carried in or adopted ^[7].
  • Colony: Optionally polygyne, Supercolonial
• Size & Growth:
  • Queen: Not particularly large compared to workers, this morphological feature suggests possible temporary social parasitism ^[2]. Exact measurements not specified in available literature.
  • Worker: 4.5-7mm ^[2][8]
  • Colony: 260-51,000 workers per nest, averaging 6,800. The Ishikari supercolony contains approximately 306 million workers across 45,000 nests ^[1][6].
  • Growth: Moderate, breeding season is delayed compared to European species due to severe winters. Eggs appear in early May, larvae in June, pupae in early-mid July, and new adults emerge in late July to mid-September ^[6].
  • Development: Approximately 10-14 weeks from egg to worker at optimal summer temperatures. Eggs appear mostly in late May, larvae through June to late August, pupae July to September, with adults emerging late July through mid-September ^[6]. This delayed timeline compared to European Formica species is due to prolonged winter hibernation. (Development is highly seasonal, eggs first appear in early May (not March-April like European species), with adult emergence not until late July. This short breeding season is caused by prolonged severe winter with snow cover from December to March.)
• Antkeeping:
  • Temperature: Keep nest area at 20-25°C during active season (May-September). The species is adapted to temperate conditions with cold winters, room temperature is generally suitable. Provide a temperature gradient allowing workers to choose their preferred zone.
  • Humidity: Moderate humidity. In nature, nests are made under root systems of grasses in sandy coastal areas. Keep nest substrate moist but not waterlogged. The brood section is located immediately beneath ground level (0-20cm deep) in areas with fine root systems ^[4].
  • Diapause: Yes, hibernation is essential. Colonies hibernate from November to April (approximately 5-6 months). Workers become active again in mid-April just after thaw, with full activity starting in late May when honeydew becomes available ^[9]. During hibernation, nests have deep vertical shafts (85-125cm deep) filled with aggregations of workers ^[7].
  • Nesting: Y-tong (AAC) or plaster nests work well for colonies. In nature, they build discrete nests under grass root systems with a loose thatch mound made from dead grass and conifer needles. Brood chambers are typically 1-3cm high and 3-20cm wide, located 0-20cm deep. Provide a nest with multiple chambers and adequate depth for the colony to organize brood areas. The species is polydomous in the wild, you could connect multiple nest modules to simulate their natural multi-nest structure.
• Behavior: Formica yessensis is an aggressive species, particularly during the breeding season (June-July) when up to 33% of workers may exhibit aggressive behavior when the nest is disturbed ^[6]. Workers readily attack and swarm in response to interference. They are aphid-tending specialists, their diet is primarily honeydew from aphids (especially Tuberculatus quercicola), with additional protein from insects ^[9]. Workers show clear task polyethism based on size: smaller workers (under 1.2mm) perform intranidal tasks and aphid-tending, while larger workers (over 1.48mm) specialize in hunting and external activities ^[10]. Escape prevention is important for medium-sized ants, they are not tiny but can climb well. Use standard ant escape prevention (Fluon on rim edges).
• Common Issues: aggressive defense behavior, colonies may swarm aggressively when nest is disturbed, especially during summer breeding months, cold sensitivity, delayed development means colonies need warm summer conditions (20-25°C) to complete their short breeding season, aphid dependency, diet is primarily honeydew, colonies may struggle without consistent access to sugar sources or aphid colonies, hibernation failure, colonies require proper cold period (November-April) or they may become confused about seasonal timing, polydomous stress, in captivity, single-nest housing may stress colonies adapted to multi-nest networks, consider connecting multiple nest modules

Housing and Nest Setup

Formica yessensis is best housed in a Y-tong (AAC) or plaster formicarium with multiple chambers. In the wild, they build nests under grass root systems with a loose thatch mound, so provide a nest with a dirt area or chamber where they can arrange their brood. The brood section in natural nests is located 0-20cm deep with chambers 1-3cm high and 3-20cm wide ^[4]. Because they are polydomous (multi-nest) in nature, consider connecting two or three nest modules with tubing to give them a more natural colony structure. Use a standard outworld for foraging with a water test tube as a humidity station. Escape prevention is important, apply Fluon to the rim of the nest and outworld lid.

Feeding and Diet

This species is primarily a honeydew specialist. In the wild, their diet comes mainly from aphid honeydew (particularly Tuberculatus quercicola on oak trees), with additional protein from hunting insects ^[9]. In captivity, provide a constant sugar source (sugar water, honey, or diluted maple syrup) and protein-rich foods like small insects (mealworms, crickets, fruit flies). They will also attend aphid colonies if you establish them on a plant in the outworld. The number of workers attending aphids varies seasonally, peaks in late June, declines in late July, then increases again from late July to late August ^[9]. Feed protein 2-3 times per week and keep sugar water available at all times.

Temperature and Seasonal Care

Keep the nest area at 20-25°C during the active season (May-September). This species has a delayed breeding cycle compared to European Formica, eggs appear in early May, larvae in June, pupae in early-mid July, and new adults emerge late July through mid-September ^[6]. The delay is due to prolonged winter hibernation (snow cover December-March). During winter (November-April), you must provide a cold period. Reduce temperature to 5-10°C or place the colony in an unheated garage or refrigerator for 4-5 months. Without proper hibernation, colonies become confused about seasonal timing and may fail to breed properly. In spring (mid-April), workers become active again after thaw, with full activity starting in late May when honeydew becomes available.

Colony Structure and Multi-Queen Dynamics

F. yessensis is highly polygynous, each nest contains multiple queens (1-213,averaging 24) ^[6]. Unlike many polygynous species, they readily accept foreign queens and workers from neighboring nests within the supercolony. Studies show almost no internidal hostility, workers can be transferred 20km between nests and are accepted ^[11]. New colonies form through budding: a group of workers departs from the mother nest, establishes a new site, and queens are either carried in or newly mated queens are adopted after nuptial flights ^[7]. In captivity, you can keep multiple queens in one nest, they will coexist peacefully. The queen-worker ratio is approximately 1:340,much lower than in some other Formica species ^[6].

Behavior and Defense

This species is notably aggressive, especially during the breeding season. When disturbed, up to 33% of workers may rush out aggressively, this percentage is highest in June and July ^[6]. Workers show clear size-based task specialization: smaller workers (under 1.2mm body width) tend aphids and perform inside-nest tasks, while larger workers (over 1.48mm) specialize in hunting and external activities ^[10]. They are effective predators on insects and play an important role in pest control, in Korea, they have been studied for controlling pine caterpillar moths. Their aggressive defense makes them excellent at monopolizing aphid colonies but requires careful handling during nest maintenance.

Nuptial Flights and Reproduction

Nuptial flights occur in late July to mid August, typically in early morning between 5:00 and 8:20 ^[11]. Males and females emerge onto the nest surface, climb nearby plants, and take flight. The sex ratio is approximately 1:1. Copulation lasts 30 seconds to 9 minutes, with queens capable of mating multiple times ^[12]. After mating, most fertilized queens return to their mother nest or enter adjacent nests on foot rather than flying away, this behavior contributes to supercolony formation ^[11]. Only a small fraction of mated queens fly away to establish new colonies. The percentage of nests producing sexuals (fertile nests) is relatively low, only about 6-14% of nests produce alates each year ^[11].

Frequently Asked Questions

References