Lasius alienus (The Cornfield Ant)

Lasius alienus, commonly known as the Cornfield Ant or the Pale Garden Ant, is a ubiquitous and fascinating species that often plays second fiddle to its more famous cousin, Lasius niger. However, for the discerning ant keeper and the curious naturalist, Lasius alienus offers a wealth of complex behaviors and a subtle beauty that makes it a staple of the Holarctic ant fauna. Found across both Europe and North America, this species is a master of the subterranean realm, thriving in environments ranging from open meadows and cornfields to the edges of forests and domestic gardens. While it may appear as just another small black ant to the untrained eye, Lasius alienus possesses a distinct ecological niche and a suite of survival strategies that have allowed it to colonize vast swathes of the northern hemisphere.

Natural History and Identification

Lasius alienus belongs to the subfamily Formicinae, a group known for their lack of a functional sting and their use of formic acid for defense. Physically, workers are small, typically measuring between 2.0mm and 3.5mm. They are generally a dark brown to brownish-black color, often appearing slightly paler or more "matte" than the glossy Lasius niger. One of the primary diagnostic features used by myrmecologists to distinguish alienus from niger is the absence of standing hairs on the antennal scapes and the tibiae of the legs—Lasius alienus is much less "hairy" than its black garden ant counterpart.

The queens are significantly larger, ranging from 7mm to 9mm, and are robust, dark-bodied insects. They are prolific layers and are remarkably hardy, capable of founding colonies pleometrotically (with multiple queens) in the initial stages, although they eventually transition to a monogynous state where only one queen survives as the colony matures. Males are smaller and more wasp-like, appearing in large numbers during the peak of the summer during nuptial flights.

Distribution and Native Habitat

The distribution of Lasius alienus is truly impressive, spanning the temperate regions of Europe, North Africa, and much of North America. In North America, recent taxonomic revisions have identified several closely related species previously lumped under the name "alienus" (such as Lasius americanus), but the broader "alienus-group" remains a dominant force across the continent. They prefer slightly drier and more open habitats than Lasius niger. You will frequently find them in sandy soils, well-drained grasslands, and, as their common name suggests, agricultural fields where the soil is frequently disturbed.

In the wild, their nests are primarily subterranean. They do not build large mounds; instead, their presence is often signaled by small craters of excavated soil or "volcanoes" around the entrance holes. These nests can extend deep into the earth, allowing the colony to regulate temperature and humidity by moving larvae and pupae between different chambers throughout the day.

Diet and Foraging Behavior

Lasius alienus is a generalist omnivore with a particular penchant for liquid sugars. Their relationship with aphids is one of the most studied aspects of their behavior. Unlike some ants that forage primarily on the surface, Lasius alienus is a specialist in "tending" root aphids. They will actually construct small chambers around the roots of plants where aphids reside, protecting the sap-sucking insects from predators and in return harvesting the sweet honeydew they excrete. This subterranean ranching allows the ants to access a consistent food source without exposing themselves to the dangers of surface foraging.

However, they are also active surface foragers, especially during the night or on overcast days. They scavenge for dead insects, hunt small invertebrates, and are frequent visitors to floral nectaries. In the home or garden, they may occasionally be seen scouting for spilled sweets or crumbs. For the ant keeper, this means they are incredibly easy to feed, accepting a wide variety of protein sources (fruit flies, crickets, mealworms) and sugar sources (honey-water, sugar-water, or specialized ant nectars).

Colony Lifecycle and Social Structure

The life of a Lasius alienus colony begins with the nuptial flight. These events are often synchronized with weather patterns, usually occurring on warm, humid afternoons in late July or August, often following a rainstorm. Thousands of winged queens and males take to the skies in a massive mating swarm. After mating, the queen sheds her wings and searches for a suitable nesting site in the soil. She is a claustral founder, meaning she will seal herself in a small chamber and raise her first generation of workers (nanitics) using only her stored fat reserves and the energy from her metabolized wing muscles.

Once the first workers emerge, they take over the duties of foraging and nest expansion. A mature colony of Lasius alienus can contain several thousand individuals. Their social structure is highly organized, with workers performing different tasks based on their age (temporal polyethism)—younger workers typically stay inside the nest to care for the brood, while older workers venture out to forage and defend the territory.

Ant Keeping: Care and Housing

Lasius alienus is an excellent species for both beginners and experienced hobbyists. Their hardiness and moderate growth rate make them a rewarding species to observe. One of the most critical aspects of their care is providing a proper diapause (hibernation). As a temperate species, they require a period of cold rest from late October through March. During this time, the temperature should be lowered to between 5°C and 10°C (41°F - 50°F) to simulate winter. Failure to provide a proper hibernation can lead to a decline in queen productivity and colony health over time.

During the active season, they should be kept at standard room temperatures (20°C - 25°C). They are sensitive to desiccation, so maintaining a moisture gradient in the nest is essential. A setup that allows one end of the nest to remain damp while the other stays dry allows the ants to choose the optimal environment for different stages of brood development.

Recommended Setup

Because Lasius alienus is a relatively small and highly adaptable species, they do exceptionally well in compact, well-designed formicaria. For founding queens and small colonies, the All-in-One setup is ideal, as it provides a controlled environment with integrated foraging space. As the colony grows into the hundreds or thousands, transitioning them to a Paris model formicarium is highly recommended. The Paris setup offers excellent visibility and the precise humidity control that subterranean species like Lasius alienus crave. Its sleek design mimics the tight vertical and horizontal chambers they would naturally excavate in the soil.

Fun Facts and Advanced Observations

• Chemical Warfare: When threatened, Lasius alienus workers will spray formic acid from their acidopore. In a confined space, the smell is often compared to a sharp, vinegary scent.
• The "Invisible" Ant: Because they spend so much of their time tending root aphids underground, a garden may have dozens of Lasius alienus colonies that go completely unnoticed by the human inhabitants.
• Long-Lived Queens: Like many Lasius species, the queens of Lasius alienus are remarkably long-lived. While wild queens face many dangers, in a laboratory or home setting, they can live for over a decade, providing many years of observation for the keeper.
• Nesting with Others: Lasius alienus is sometimes found nesting in close proximity to other ant species. While they defend their territory vigorously, they are often more "timid" than Lasius niger and will use evasion and subterranean tunnels to avoid direct conflict with larger, more aggressive species.