Lasius interjectus (The Larger Citronella Ant)

Lasius interjectus, commonly known as the Larger Citronella Ant, is one of the most chemically fascinating species in the North American ant fauna. Named for the distinct, pungent lemon or citrus-like odor it emits when disturbed or crushed, this ant is a specialist of the subterranean world. However, unlike the more common garden ants, Lasius interjectus follows a complex and ruthless life strategy known as temporary social parasitism. For the ant keeper, this species represents a "master class" in myrmecology, requiring a deep understanding of colony founding and the delicate balance of inter-species social dynamics.

Natural History and Identification

Lasius interjectus belongs to the subgenus Acanthomyops, a group of ants characterized by their bright yellow to orange-gold coloration and their powerful chemical defenses. The workers are medium-sized for the genus, typically measuring between 3.5mm and 4.5mm. They have small eyes and relatively short, thick antennae, adaptations suited for a life spent entirely in total darkness. Their bodies are covered in fine, silky hairs that give them a slightly shimmering appearance under a microscope.

The queens are the truly striking members of the species. They are much larger than the workers, often reaching 8mm or more, with a robust gaster and a deep reddish-orange or dark amber color. The most diagnostic feature of this species is the "citronella" scent, which is produced by mandibular glands and serves as a powerful alarm pheromone and defensive repellent against predators and rival ant colonies. When a nest of Lasius interjectus is uncovered, the air is often immediately filled with the scent of fresh lemons.

Distribution and Native Habitat

Lasius interjectus is native to North America, with a range that extends from southern Canada through the eastern and central United States, reaching as far west as the Rocky Mountains. They are common in a variety of habitats, including deciduous forests, old fields, and suburban backyards. They prefer well-aerated, slightly moist soil and are frequently found nesting under large flat stones, decaying logs, or the foundations of houses.

In the wild, their nests are entirely subterranean. They rarely, if ever, forage on the surface. Their presencia is most often noticed by homeowners during the winter or early spring, when colonies nesting near house foundations may accidentally wander into basements or crawl spaces during their activity cycles, or when massive nuptial flights occur in the vicinity.

Diet and Foraging Behavior

The diet of Lasius interjectus is highly specialized. Like other members of the "yellow ant" group, they are almost entirely dependent on the honeydew produced by subterranean aphids and mealybugs. They "farm" these insects on the roots of trees, shrubs, and grasses, providing them with a constant, protected source of liquid carbohydrates. Because of this specialized diet, they have very little need to venture above ground.

In addition to honeydew, they are scavengers of the soil, consuming small arthropods and organic debris they encounter while expanding their tunnel networks. In captivity, Lasius interjectus can be challenging to feed. They are often uninterested in surface-offered proteins and sugars initially. Successful keepers often use specialized liquid feeders and offer very soft, easy-to-digest protein sources like fruit fly larvae or freshly killed pinhead crickets, placed as close to the nest entrance as possible to encourage foraging.

Colony Lifecycle and Social Parasitism

The most remarkable aspect of Lasius interjectus is its method of colony founding. Unlike "claustral" queens that can start a colony on their own, a Lasius interjectus queen is a temporary social parasite. After her nuptial flight, she does not dig a hole and lay eggs. Instead, she must find a host colony—usually of the Lasius alienus or Lasius neoniger species group. She will infiltrate the host nest, often using her citronella scent to confuse the host workers or by mimicking the host colony's chemical signature. Once inside, she will eventually kill the host queen and take her place.

The host workers will then begin to care for the Lasius interjectus queen and her offspring. Over time, as the original host workers die off and are replaced by the interjectus workers, the colony transitions from a mixed nest to a pure Lasius interjectus colony. This parasitic phase makes them extremely difficult to start from a single queen in captivity, as the keeper must provide "host" workers and pupae for the queen to successfully establish herself.

Ant Keeping: Care and Housing

Lasius interjectus is generally considered an advanced species for ant keeping due to the parasitic founding requirements and their subterranean nature. However, once a colony is established, they are hardy and long-lived. They require very high humidity levels and a complete lack of light in the nesting area. They are also highly sensitive to vibrations; a colony kept in a high-traffic area will often become stressed, leading to brood-eating or queen death.

Like all temperate Lasius, they require a winter diapause. A period of 3-4 months at temperatures between 5°C and 10°C is essential for their long-term health. During this time, it is vital to ensure the nest does not dry out, as the ants are inactive and cannot move to more humid areas as easily.

Recommended Setup

Because of their subterranean specialization and need for high humidity, the All-in-One setup is a great starting point for smaller established colonies. It allows for a tightly controlled environment. However, the Paris formicarium is the ultimate choice for a thriving Lasius interjectus colony. The absorbent material of the Paris nest provides the consistent moisture levels these ants need, and the layout of the chambers allows the queen to find a secure, dark retreat while the workers manage their "ranching" activities in the peripheral chambers. For keepers who want to witness the full scale of their tunnel-building, the Large Habitat Kit with a soil-based setup can be used, though visibility will be significantly reduced.

Fun Facts and Advanced Observations

• The Lemon Scent: The citronella scent is so strong that it has been known to linger on a person's hands for hours after handling a colony. It is primarily composed of the chemical compounds citronellal and neral.
• Late-Season Flights: Lasius interjectus often has very late nuptial flights, sometimes occurring as late as October or even November in some regions, earning them the nickname "winter ants" in some older literature (though they are not the true winter ant, Prenolepis imparis).
• Subterranean Engineers: They are known to build extensive galleries that can follow the foundation of a house for dozens of feet, exploiting the warmth and moisture found near human structures.
• Chemical Camouflage: Researchers are still studying the exact mechanisms the queens use to infiltrate host nests. It is believed they may actively "rub" themselves against host workers to acquire the colony's scent before attempting to enter the inner sanctum of the nest.