Pests after a flood

Mosquitoes

Heavy rain can actually flush out some breeding sites, but as water recedes and puddles stagnate, disease-carrying mosquitoes return after a few weeks, and floodwater mosquitoes can be a heavy nuisance in the meantime. Keep repellent handy during cleanup, especially at night.^[3]

CDC describes the same two waves. Adult mosquitoes generally don't survive a hurricane's high winds. Then the flooding hatches eggs that floodwater mosquitoes laid in the soil during earlier floods, which produces very large numbers of mosquitoes that are mostly nuisance biters and in general don't spread viruses that make people sick.^[1]

The kinds that can spread viruses may increase 2 weeks to 2 months after a hurricane, CDC says, especially in places that didn't flood but got more rain than usual. In Texas, AgriLife's Mike Merchant named the southern house mosquito, the main carrier of West Nile virus there, as the one that comes back once puddles stagnate.^[1][3]

• Repellent: use an EPA-registered product with DEET, picaridin, IR3535, oil of lemon eucalyptus (OLE), para-menthane-diol (PMD) or 2-undecanone, and follow the label. Don't use OLE or PMD products on children under 3.^[11]
• Mosquitoes bite day and night, so cover up with loose long sleeves and long pants during cleanup, not only at dusk.^[11][1]
• Once a week, empty and scrub, turn over, cover or throw out anything that holds water: tires, buckets, toys, pools, birdbaths, flowerpot saucers and trash containers.^[11]
• Clean up debris and trash outside the house as soon as you can.^[1]

Rodents

After a hurricane or flood, rats, mice and other pests may move into homes and buildings. They can spread diseases, bite people or pets, and trigger asthma attacks or allergic reactions in some people.^[1]

• Cover or close holes in walls; some rodents can squeeze through holes as small as a dime.^[1]
• Store food and water in thick plastic, glass or metal containers with tight-fitting lids.^[1]
• Clean droppings with CDC's wet method: ventilate, soak with disinfectant, then wipe up.^[5]
• Buildings that sat empty for a long time may be infested. CDC says airing them out for 2 to 3 days before going back in may help, and if there are signs of rodents, ask your local health department how to clean.^[1]
• Before cleaning droppings in a room, open the doors and windows for 30 minutes and leave the area while it airs out.^[5]
• Put on rubber or plastic gloves. Spray the urine and droppings with a disinfectant, or a bleach solution of 1.5 cups of household bleach in 1 gallon of water, until soaked, and let it sit 5 minutes or as long as the label says. Wipe up with paper towels and throw them out in a covered garbage can.^[5][1]
• Trap rodents still in the house with spring-loaded snap traps. Wearing gloves, seal each dead rodent in two plastic bags and throw it away.^[1][5]
• Wash gloved hands before taking the gloves off, then wash your hands with soap and warm water.^[5]
• Throw out trash as soon as you can, in a covered can or dumpster, and wash dishes and cooking gear after each use.^[1]

Snakes and other animals

Floods force snakes out of their usual habitat and into places where people don't expect them, including homes. Be careful when you return.^[1]

• Snakes may swim toward higher ground or hide under debris; be careful when moving piles.^[1]
• If someone is bitten, keep them still and calm and get medical care.^[1]
• Avoid wild or stray animals, let local authorities handle them, and remove animal carcasses.^[1]
• Wear boots and long pants, wear leather gloves when you handle brush and debris, stay away from leaf piles, and don't climb on wood piles where a snake could be hiding.^[12]
• Never handle a venomous snake, even a dead one or its cut-off head.^[12]
• Walking in high water, you may feel a bite and not know it was a snake. Signs can include a pair of puncture marks, redness and swelling, severe pain at the bite, nausea and vomiting, trouble breathing, disturbed vision, more saliva and sweat, and numbness or tingling in the face or limbs.^[1]
• While waiting for help: have the person lie or sit with the bite below heart level, wash the wound with warm soapy water and cover it with a clean, dry dressing. Try to remember the snake's color and shape.^[1]
• Don't use a tourniquet, cut the wound, suck out venom, put ice on it or soak it in water, and don't give alcohol or caffeinated drinks. Don't pick up the snake or try to trap it.^[1]

Floating fire ants

Fire ant colonies can link together into floating rafts, and they're more aggressive in that formation; a mat can swarm over a person or object it touches. If ants get on you, rub them off.^[3]

This is old, well-studied behavior. Rafting by the red imported fire ant has been documented for over a century. One ant struggles in water, but a linked group can float for days, and lab work found larvae in the raft improve the colony's survival.^[15][14]

AgriLife entomologist Paul Nester says a floating colony is alive and will 'explode' onto any object or person it touches, stinging to protect the queen at the center. Watch what is drifting toward you in floodwater.^[3]

• Cuffed gloves, rain gear and rubber boots keep ants off your skin while you work in floodwater.^[3]
• Fire ants can be on trees or in water, and items you lift, including animal carcasses, may be covered in ants. Look the area over before you start.^[13]
• Fire ants grip the skin with their jaws, so rub them off briskly. The stings burn, and red bumps can turn into white, fluid-filled pustules within a day or two.^[13][3]
• Antihistamines may help; follow the package and expect drowsiness. People allergic to the venom can have anaphylaxis, a severe reaction that needs emergency care, and anyone with a history of severe reactions to stings should carry an epinephrine auto-injector.^[13]

Floodwater and cleanup gear

Floodwater can carry bacteria from overflowing sewage and farm and industrial waste. Skin contact alone isn't a serious health risk, CDC says, but eating or drinking anything floodwater touched can make you sick.^[7]

• Wear rubber boots and waterproof gloves for cleanup, and goggles as well if sewage is involved.^[7][2]
• Keep cuts and sores that will be in floodwater as clean as you can: wash with soap and put antibiotic ointment on them. Know when you had your last tetanus shot in case of a puncture wound.^[7][2]
• In water cooler than 75 degrees F, wear insulated clothes and boots, take frequent breaks out of the water and change into dry clothes when you can.^[7]
• Wait to go back in until professionals say the home is safe. Children should not take part in disaster cleanup, and people with asthma or weakened immune systems should stay away from moldy buildings.^[9]

Drying out and mold

Drying the house fast is the step that matters most for mold. CDC's cleanup guidance and EPA say to dry water-damaged areas and items within 24 to 48 hours; if you couldn't, CDC says to assume mold is growing. CDC's public service message gives a longer window, 48 to 72 hours.^{[7][9][10][8]}

• Open doors and windows, including closets, cabinets and the attic access, and use a wet vacuum on standing water. Once the power is safe, run fans and dehumidifiers, but don't use fans after mold has started to grow, because they can spread it.^[9][7]
• Throw out what can't be cleaned and dried quickly: mattresses, carpet and padding, upholstered furniture, pillows, stuffed animals, books and paper. Remove drywall and insulation that sewage or floodwater soaked.^[7][2]
• For mold work, wear at least an N-95 respirator, goggles without open vent holes, and non-latex, vinyl, nitrile or rubber gloves.^[9][7]
• CDC's bleach mix is 1 cup of household bleach per gallon of water, used with windows open. Never mix bleach with ammonia or any other cleaner.^[7][8]
• Don't paint or caulk over mold. Fix the water problem and clean the mold off first.^[9][10]
• If mold covers more than about 10 square feet, EPA points to its remediation guidance and CDC suggests considering a professional.^[10][8]
• Mold exposure can cause asthma attacks, eye and skin irritation and allergic reactions, and severe infections in people with weakened immune systems. If symptoms get worse after you move back in, mold may still be present.^[9]

During and after cleanup

• Bed bugs can show up where many people share close quarters, such as evacuation shelters; shelters should know what they look like and inspect sleeping areas regularly.^[3]
• Foreign grain beetles and other tiny fungus beetles feed on molds growing on damp wood, plaster and wallboard. Drying the building out, with fans and air conditioning, is the lasting fix.^[4]
• Wet wood and damp soil around the foundation favor termites; fix leaks and drainage as part of repairs.^[6]

Common questions

When do mosquitoes get bad after a flood?

Floodwater nuisance mosquitoes hatch right after the flooding. The kinds that spread viruses can increase 2 weeks to 2 months after a hurricane, so keep using repellent through that window.^[1]

Do fire ants really float in floodwater?

Yes. Colonies link their bodies into waterproof rafts that can float for days, and they sting whatever they touch. Wear cuffed gloves, rain gear and rubber boots in floodwater.^[14][3]

Should I sweep up mouse droppings after a flood?

No. Don't sweep or vacuum droppings or urine. Air the room out, soak the droppings with disinfectant or bleach solution for 5 minutes, and wipe them up with paper towels while wearing gloves.^[5][1]

Why are tiny beetles showing up on my walls after water damage?

Foreign grain beetles and other fungus beetles feed on mold growing on damp wood, plaster and wallboard. They fade as the building dries out; fans and air conditioning speed that up.^[4]

Sources

1. U.S. Centers for Disease Control and Prevention, “What to Do to Protect Yourself From Animals After a Disaster (reviewed August 26, 2026).” www.cdc.gov/natural-disasters/response/what-to-do-protect-yourself-from-animals-after-a-disaster.html (accessed 2026-11-10)
2. U.S. Centers for Disease Control and Prevention, “Preparing for Floods (reviewed August 24, 2026).” www.cdc.gov/floods/safety/index.html (accessed 2026-11-10)
3. Texas A&M AgriLife Today, “Texas A&M AgriLife entomologists: Floating fire ants, insect pests among flood hazards (August 30, 2017).” agrilifetoday.tamu.edu/2017/08/30/texas-am-agrilife-entomologists-floating-fire-ants-insect-pests-among-flood-hazards/ (accessed 2026-11-10)
4. University of Kentucky Entomology, “ENTFACT-610: Foreign Grain Beetle (revised March 2026).” entomology.mgcafe.uky.edu/ef610 (accessed 2026-11-10)
5. Centers for Disease Control and Prevention, “How to Clean Up After Rodents.” www.cdc.gov/healthy-pets/rodent-control/clean-up.html (accessed 2026-11-10)
6. University of Kentucky Entomology, “ENTFACT-605: Protecting your Home Against Termites (revised March 2026).” entomology.mgcafe.uky.edu/ef605 (accessed 2026-11-10)
7. U.S. Centers for Disease Control and Prevention, “Guidelines for Cleaning Safely After a Disaster (reviewed August 26, 2026).” www.cdc.gov/natural-disasters/safety/index.html (accessed 2026-11-10)
8. U.S. Centers for Disease Control and Prevention, “Preventing Mold (natural disasters PSA, reviewed August 26, 2026).” www.cdc.gov/natural-disasters/psa-toolkit/preventing-mold.html (accessed 2026-11-10)
9. U.S. Centers for Disease Control and Prevention, “Homeowner's and Renter's Guide to Mold Cleanup After Disasters (June 2015).” www.cdc.gov/mold-health/media/Homeowners_and_Renters_Guide.pdf (accessed 2026-11-10)
10. U.S. Environmental Protection Agency, “A Brief Guide to Mold, Moisture and Your Home.” www.epa.gov/mold/brief-guide-mold-moisture-and-your-home (accessed 2026-11-10)
11. U.S. Centers for Disease Control and Prevention, “Preventing Mosquito Bites.” www.cdc.gov/mosquitoes/prevention/index.html (accessed 2026-11-10)
12. U.S. Centers for Disease Control and Prevention, “Venomous Snakes at Work (NIOSH).” www.cdc.gov/niosh/outdoor-workers/about/venomous-snakes.html (accessed 2026-11-10)
13. U.S. Centers for Disease Control and Prevention, “Insects and Scorpions at Work (NIOSH).” www.cdc.gov/niosh/outdoor-workers/about/insects-and-scorpions.html (accessed 2026-11-10)
14. Proceedings of the National Academy of Sciences, “Mlot NJ, Tovey CA, Hu DL. Fire ants self-assemble into waterproof rafts to survive floods. PNAS 2011;108(19):7669-73 (PMID 21518911).” pubmed.ncbi.nlm.nih.gov/21518911/ (accessed 2026-11-10)
15. Journal of Insect Science, “Adams BJ et al. Raft formation by the red imported fire ant, Solenopsis invicta. J Insect Sci 2011;11:171 (PMID 22950473).” pubmed.ncbi.nlm.nih.gov/22950473/ (accessed 2026-11-10)