Paratrechina longicornis (Latreille, 1802)

Crazy ant

The ant that runs like it is panicking, long-legged, erratic, and unmistakable in motion.

Order: Hymenoptera
Family: Formicidae
Group: Ants
Ontario status: Not established outdoors in Ontario; occasional heated-building records, tropical species

Why it matters

A food contaminator where it establishes indoors; in the US South it is a major tramp-ant pest. In Ontario it is an occasional indoor curiosity and an identification reference.

Origin

Tropical in origin (likely Asia or the Pacific); spread worldwide with shipping and now common in warm regions.

Behavior

Famous for its erratic, jerky, high-speed running, it looks 'crazy' compared to the orderly trails of other ants. Forages day and night.

Living conditions

Needs year-round warmth. In Ontario it can only survive inside heated buildings, it does not live outdoors here.

Signs of presence

Fast, jerky, direction-changing ants unlike any orderly trail
Very long legs and antennae visible even without magnification
Activity in warm, moist indoor areas

Weaknesses

Killed by cold, cannot survive an Ontario winter outdoors
Needs constant indoor warmth and moisture
Erratic foraging makes it conspicuous and easy to spot

Myths and facts

Myth Erratic movement means the ants are poisoned.
Reality The jerky running is normal for this species, it is how it got its name.

Research notes

Morphology

Workers 2.2-3 mm, dark brown to black, slender. Exceptionally long legs and 12-segmented antennae (scape exceeding head by half its length). Single node; body with long coarse hairs.

Diagnostics

Confirm by erratic rapid movement + very long legs/antennae + single node. Movement alone is nearly diagnostic.

Easily confused with

Odorous house ant, Tapinoma sessile Odorous house ant moves in orderly trails and smells of rotten coconut when crushed; crazy ant moves erratically with no odor.

Life cycle

Adult: Workers live ~2-3 months.
Egg: Eggs hatch in ~2 weeks at warm temperatures.
Egg to adult: ~5-7 weeks at warm temperatures
Generations per year: Continuous in heated buildings
Nymph or larva: Legless larvae; pupae in cocoons.

Development

Complete metamorphosis: egg → larva → pupa → adult.

Reproduction

Multiple queens (highly polygynous); colonies bud readily; colonies can be very large.

Distribution

Global: Pantropical; heated buildings in temperate zones
Native range: Likely tropical Asia or Pacific
Ontario: Not established outdoors; sporadic heated-building interceptions

Ecology

Opportunistic omnivore; nests in any sheltered warm crevice, soil, wall voids, potted plants. Foraging is rapid and seemingly random but chemically guided.

Resistance

Limited published data.

IPM implications

In Ontario, occurrence is sporadic and building-limited, locate the indoor harborage (warm, moist voids; plant soil) rather than treating perimeters. Budding biology means disturbance-tolerant, colony-level approaches apply as with other polygynous tramp ants.

Chemical ecology

Trail and recruitment pheromones studied as models of mass foraging; erratic individual movement with coordinated colony-level recruitment.

Genetics and DNA

No reference genome published as of 2026.

Taxonomy

Order Hymenoptera, family Formicidae, subfamily Formicinae, genus Paratrechina. Described by Latreille, 1802. Pantropical tramp species.

Open questions

Overwintering potential in Ontario's urban heat islands under climate warming.

References

Hölldobler, B. & Wilson, E.O. 1990, The Ants, Harvard University Press
Mallis Handbook of Pest Control