Tawny 'crazy ants' are invading the US and disrupting ecosystems

Florida has a new household headache that does not respect lawns, fence lines, or even the electronics on your porch. People notice the swarming first, then the silence that follows when other insects vanish.

Many folks call them yellow crazy ants, but the species spreading across Florida is the tawny crazy ant, Nylanderia fulva.

This is an invader from South American with a jittery gait and a talent for building huge colonies. It is different from the yellow crazy ant found on the Pacific and Indian Ocean islands, and it is the one Floridians keep running into.

Tawny crazy ant antics

Tawny crazy ants do not fly at you or sting like fire ants. They run in rapid, erratic lines, and they show up in numbers that feel out of scale to a backyard.

They move queens and workers into many shallow nests, spreading through leaf litter, under stones, and around woodpiles. The spread feels steady at first, then it surges.

These ants swarm food sources and guard sweet liquids from plant pests, which gives them steady fuel. That steady fuel helps their numbers jump in warm months.

They do not act like a normal backyard ant colony with a clear border. Their social structure is loose enough that neighboring nests share workers and food.

How they build supercolonies

Scientists use the term supercolony to describe a network of nests that act like one giant colony. Workers from distant nests do not fight, and queens can move freely among nests.

USDA research found that tawny crazy ants collected from nests as far as 270 miles (435 kilometers) apart showed no aggression towards each other. That absence of territorial behavior lets their populations scale across entire neighborhoods.

A report captured what overrun sites looks and sounds like to field teams. “There’s no insect noise and there’s no bird noise,” described Edward LeBrun, ecologist at the University of Texas at Austin (UT).

That kind of silence points to impacts up the food web. When insects disappear, birds and reptiles lose prey, and that ripples through a local ecosystem.

Invading homes and electronics

A University of Florida Institute of Food and Agricultural Sciences factsheet notes that tawny crazy ants are attracted to electrical equipment.

It also documents attacks on honeybee hives, crops, and native ant species. These ants prey on a range of small animals, including birds and insects, with some deaths caused by asphyxia.

Large numbers can clog switches and short out contacts. Once they establish near a structure, they trail inside through tiny gaps around doors, windows, and utility penetrations.

People sometimes try bait or a quick perimeter spray and expect a clean win. The colony structure makes that unlikely, because reinvasion from nearby nests can be constant.

Simple yard hygiene reduces the pressure at the edges. Trim branches off the house, store trash away from walls, and clear stacked lumber and leaf litter that provide cover.

Tawny ant feeding strategies

Tawny crazy ants are omnivores that sip sugary honeydew from sap sucking insects and harvest protein from other arthropods. They also scavenge, which is why you might see them overwhelm a dead lizard or a fallen insect in minutes.

They bite rather than sting. Worker ants deploy formic acid from a nozzle-like opening called an acidopore, which they use in close contact fights against other insects.

On open ground, their advantage is sheer volume. Ants pour over competitors and quickly control the space around food.

In trees and shrubs, they protect honeydew producers and move them between plants. That behavior spreads plant stress and, in some cases, disease.

Where they’ve spread

A UF IFAS update documents confirmed infestations across at least 27 Florida counties as of 2014, and also across the Gulf Coast. New county records continue to appear as survey work expands.

Florida’s mix of warm winters, moisture, and heavy plant cover suits this ant well. That is why neighborhoods near water or with dense landscaping often report the earliest pressure.

Movement often follows people. Nursery stock, mulch piles, and equipment can carry small colonies or queens.

Once they arrive, the pattern is familiar. Numbers spike in spring and summer, settle back in cooler months, then surge again.

Controlling tawny ants

With these ants, the goal is suppression, not instant eradication. UF IFAS IPM guidance stresses sanitation, habitat modification, and targeted insecticide use coordinated at the community level.

Professionals often time treatments for early spring, before populations expand from winter sites. That timing slows the seasonal surge and helps other steps work better.

Homeowners can help by sealing exterior gaps and reducing moisture and clutter. Food and water control indoors cuts trailing and nesting pressure.

Coordination matters because a single lot rarely stands alone. If one property clears out ants and the neighbor does not, reinvasion is likely.

A new biological tool may help

A peer reviewed paper reports that infection by a microsporidian pathogen, Myrmecomorba nylanderiae, can drive local populations of tawny crazy ants to collapse.

In long term tracking, 62 percent of infected local populations disappeared over nine years.

Researchers also tested careful introductions of the pathogen at two Texas sites. Within two years, tawny crazy ants were eliminated at both.

That does not mean ants vanish everywhere overnight. It suggests a path for biological control that targets this ant while sparing native species.

Public agencies will need protocols to use that tool responsibly. Field monitoring, lab diagnostics, and clear thresholds will guide where its use is appropriate.

Photo: Joe MacGown, Mississippi State University, Bugwood.org.

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