Tim Downs, an author of thriller novels, uses bugs to tell the story of death in New Orleans caused by Hurricane Katrina. His novel “First the Dead” follows the buggy trail of forensic entomologist Nick “Bugman” Polchak as he solves murder cases using the clues left by insects.

Now, life imitates art. Nearly four years after Katrina in real-life New Orleans, entomologists say a change in the ecosystem has caused some bugs to proliferate and others to die off.

Danielle Taylor was one of the first evacuees to return to her neighborhood after Hurricane Katrina. She noticed a lot of flies and mosquitoes.

“We called them Katrina flies,” she said.

It’s no surprise that flies flourished, considering all the refrigerators with rotting food sitting on the sides of roadways. But other differences were not so immediately noticeable.

The poisonous brown widow spider is more common. Mosquitoes and some species of ants also have increased.

But not all bugs are doing well. The fire ant’s population has diminished. And in a display of how ecology works, without the fire ant to prey upon it, the sugarcane borer has increased. That in turn has meant more damage to sugar cane crops, which has meant less revenue for farmers.

Edward Martin, an entomologist who owns a local Terminix franchise, said the brown widow spider became more evident after the storm. He said he hadn’t seen a brown widow in all the time he’d worked in the area – since 1960 – until after the storm.

“Within a year or two,” he said, “they were everywhere.”

Jayme Necaise, an entomologist and director of animal and visitor programs at the Audubon Insectarium, said the massive influx of building and garden materials from other states, such as Florida, were to blame for bringing in the spiders. He said no one was inspecting all the materials coming in to Louisiana to rebuild homes.

Zena Ezeb has seen brown spiders, in her house and outside. She said that she sees them the most when she opens her door.

Usually she is not scared of spiders, but these particular spiders scare her.

“The thing that scares me is that they look deadly,” she said.

Necaise said the brown widow thrives in an undisturbed habitat with no human activity, such as abandoned houses and buildings, which have been plentiful since the storm.

“The brown widow has become quite established here in the New Orleans area,” he said.

The spider has a yellow-to-orange hourglass marking, according to the Louisiana State University Agricultural Center; it may be gray or tan to dark brown and 1 to 1.5 inches long. The best way to control the spider is to remove trash piles or other areas where they nest and by sealing cracks around doors and windows, the center advised.

Necaise said anyone who is rebuilding should be aware of the brown widow, especially   construction workers operating in undisturbed areas. The university agriculture center said that people should wear long-sleeved shirts and long pants. Necaise urged people to wear leather gloves, because spiders are unable to bite through leather. While the brown widow is not as aggressive as a black widow, its bite can be severe.

Meanwhile, a particular mosquito also has thrived in the area since the storm.

Kenneth Brown, principal research entomologist with the New Orleans Mosquito and Termite Control Board, said he noticed that the common salt-marsh mosquito, Aedes sollicitans, had become abundant as a result of high tides or heavy rain.

Necaise said the large numbers of untended and abandoned swimming pools made excellent breeding grounds for mosquitoes.

“Mosquitoes’ larvae do extremely well in water containing lots of decaying organic matter,” Necaise said. That means people who don’t want mosquitoes should drain that water.

Decaying vegetation, construction debris, empty lots and abandoned buildings also have been blamed for the rise in some varieties of ants, such as sugar ants and black ants, according to Mike Groetsch, the owner of Metro Termite and Pest Control.

But fire ants, which help to control the sugarcane borer, diminished in number because of the influx of saltwater, said Timothy Schowalter, a professor and department head of entomology at Louisiana State University. He said fire ants were eliminated in the portion of south Louisiana covered by the storm surges from Hurricanes Katrina and Rita.

That led to a tripling of the sugarcane borer population, Schowalter said, resulting in an estimated loss in revenue to the Louisiana sugarcane industry between $1.9 million and $2.9 million in 2006.

Taylor, who is dean of humanities at Dillard University, said that she thinks army ants are back after disappearing for a while.

Donald Martin agrees. “I’ve seen an increase in ants,” he said.

Martin, who lives in the Iberville neighborhood, said the proliferation of ants does not pose a problem for him: “I keep my house clean.”

Necaise said the phorid fly, a tiny insect that resembles the fruit fly and is also known as the humpbacked or scuttle fly, increased in number greatly up to a year after Katrina because there were more places to breed.

“When people aren’t around to clean up their mess, flies explode in population,” Necaise said. Their growth has since been controlled.

Schowalter has also seen an “abundance of aphids and other sap-sucking insects,” which have thrived on sprouts from trees damaged by Katrina.

Brown said it is also possible that the stinging caterpillar’s population might have increased.

Joanne Lozano said that she hates to go to her sister’s house during the spring because there are always a lot of slimy caterpillars.

Tiffany Frasier, an attendee at The New York Times Student Journalism Institute at Dillard University, thought she had been bitten by a spider but later found out she was bitten numerous times by a caterpillar. The bite mark was red, swollen, and had a ring around it.

Schowalter recalled other instances where hurricanes have transported many insects and other organisms. For example, during Hurricane Ivan in 2004, soybean rust was introduced in the South along the rim of the storm, he said. During Hurricane Katrina, and Hurricane Gustav in 2008, a variety of tropical birds appeared in the South, he added.

Taylor said she tries to avoid bugs, but it is really hard to avoid them in New Orleans.

“I watch the bugs, because I believe in killing them,” she said.