Why Fire Ants Explode After Rain in Magnolia (and How to Stop Them)

Why do fire ant mounds pop up after rain?

Rain percolates into the soil and collapses or floods fire ant tunnels, so the colony moves its brood toward the surface and piles excavated soil into a mound. The colony was already there; the rain just made it visible. Texas A&M AgriLife notes this is why spring rains make mounds easiest to find.

A fire ant mound works like a solar-heated nursery. The colony keeps eggs, larvae and pupae near the top on cool mornings and moves them deeper when the soil heats up or dries out. During a dry spell, colonies in Magnolia lawns stay mostly underground, so a yard can look clean even when it isn't.

Red imported fire ants (Solenopsis invicta) favor sunny, disturbed soil: along driveways and sidewalks, at the edge of a slab, around AC pads and in new sod. Those are the spots a technician checks first after a storm.

What happens to fire ants during a flood?

When water covers the ground, fire ant colonies link their bodies into floating rafts that can hold workers, brood and queens. The rafts drift until they hit something dry, such as a tree, fence, porch step or a person. Texas A&M advises never touching a raft; a stick or boot can become a bridge for hundreds of stinging ants.

Low areas along Spring Creek and Lake Creek and roadside ditches along FM 1488 and FM 1774 are the kinds of places where rafts collect after storms like Harvey in 2017. In laboratory studies cited by Texas A&M, floating colonies survived from a day to nearly two weeks, so the risk doesn't end when the rain stops.

Texas A&M also notes that soapy water sprayed onto a raft breaks the ants' water-repelling coating and sinks it. After the water recedes, wear boots and gloves when moving debris, and check porch steps, mailboxes, AC units and stacked items, where displaced ants often regroup.

What is the Texas Two-Step Method for fire ants?

The Two-Step Method from Texas A&M AgriLife Extension has two parts: first, broadcast a fire ant bait over the whole yard once or twice a year, ideally spring and fall; second, treat individual mounds that appear in high-traffic or sensitive spots. AgriLife describes it as less labor-intensive and less toxic than most do-it-yourself fire ant methods.

Texas A&M fire ant specialists say broadcasting bait once or twice a year can reduce fire ant colonies by 80 to 90 percent. Bait works because foraging workers carry it back and feed it to the queen and brood, which a mound drench rarely reaches.

On a large or wooded Magnolia lot, Step 1 matters most. Treating only the mounds you can see leaves many small colonies untouched in tall grass and along tree lines, and those colonies rebuild after the next rain.

When is the best time to put out fire ant bait?

Put out fire ant bait when the grass and soil surface are dry, no rain is expected for the rest of the day, and ants are actively foraging, which happens when the soil surface is roughly 70–90°F. In Magnolia that usually means spring and fall mornings or afternoons, and summer evenings when midday soil is too hot.

Texas A&M's quick test: set a potato chip or a slice of hot dog next to a mound. If ants are carrying it off within about half an hour to an hour, they are foraging and it's a good time to bait. Don't water the lawn afterward.

Baits work slowly. Fast-acting bait products typically reduce mounds within days to a few weeks, while insect growth regulator baits can take several weeks or longer because they stop the queen from producing new workers. Mounds that appear soon after baiting are not always a sign of failure.

Why doesn't pouring something on the mound work?

Mound drenches and dusts kill the ants they touch, but the queen is often deep underground or in a separate chamber, and a disturbed colony may simply relocate a few feet away. That is one reason a single mound can seem to become several after a storm. Mound treatments work best as Step 2, after a broadcast bait.

• Don't pour gasoline, bleach or other household chemicals on mounds; they are dangerous, contaminate soil and aren't labeled for fire ants.
• Don't kick or stir up a mound before treating it; that scatters the colony.
• Don't count on grits, club soda or other home remedies; they don't reliably eliminate colonies.
• Don't mow or string-trim over a fresh mound without long pants and boots.

How do you keep kids and pets safe from fire ants and fire ant bait?

Read and follow the product label, which says how long people and pets should stay off treated areas. Keep children and pets indoors while bait is spread, store bait where they can't reach it, and check play areas, sandboxes and dog runs for new mounds after every rain. Call 911 for trouble breathing, facial swelling or dizziness after stings.

Fire ant stings usually form a white pustule within about a day. Wash the area, don't break the blister, and watch for infection. Small children, older adults and pets that lie in the grass are the most likely to be stung many times at once, so mounds near play sets and dog runs should be treated first.

When Magnolia Pest Control treats a yard, the technician applies products according to their labels and tells you how long to keep kids and pets off the lawn. The written service report lists what was applied and where.

When should you call a professional for fire ants?

Call a professional when mounds keep returning after two rounds of bait, when the property is large or wooded, when ants are getting into AC units, electrical boxes or the house, or when someone in the home is allergic to stings. In Montgomery County, a professional fire ant yard treatment costs $120–$300 for a typical lot.

Fire ants are drawn to electrical equipment, and colonies inside AC disconnects, pool pump housings and utility boxes can cause shorts. Don't open electrical equipment yourself; call an electrician or HVAC technician for anything energized.

A fire ant control visit starts with a walk of the whole property, including fence lines, outbuildings and the edges of wooded areas, then a broadcast treatment matched to the season and follow-up mound treatments. If the same storms have brought mosquitoes, ask about mosquito control on the same visit, or call (281) 326-6212.