Forecast calls for an extra buggy spring and summer

April 2, 2017 5:30 AM PT

Long-legged bugs that look like mosquitoes on steroids are the first wave in what’s expected to be a prolonged inundation of insects this year in San Diego County and much of California.

Experts said heavy winter precipitation has fueled plant growth not seen since at least 2005, and that in turn should produce bumper crops of butterflies, moths, beetles, mosquitoes and even subterranean termites.

“Because of the rain we’ve had, there is an abundance of food out there. Insects are famously reproductive; they lay a ton of eggs, so if there is food available, they will get to work,” said Michael Wall, curator of entomology at the San Diego Natural History Museum.

Chris Conlan, the county’s supervising vector ecologist, put it in a more declarative way: “It’s going to be a buggy spring for sure.”

Some of the critters are downright harmless — including Tipula silvestra, the crane fly, that previously mentioned creature that resembles a gigantic mosquito (but actually has no relation to mosquitoes and doesn’t eat them). Crane flies don’t bite or sting or otherwise hurt people during their short life span.

Other insects, such as termites and caterpillars, can wreak havoc on houses and gardens with their voracious appetite. Still others are considered public-health targets because they can carry devastating, even deadly, diseases. West Nile virus, dengue fever and the Zika virus are among the threats associated with mosquitoes, which breed in lakes to pools to droplets of standing water.

“All of the conditions are right for us to see more mosquitoes this year than usual,” Wall said.

Crane flies have been the first to create a buzz in San Diego County. Conlan said residents have been dialing in for weeks to report sightings of the insects. “People call because they think they’re big mosquitoes or daddy long legs. They look imposing,” he said.

Why are there so many crane flies, often mistakenly called mosquito hawks, this year? Wall said their eggs, which are laid in soil, are best activated when exposed to certain settings.

“They do best in moist, decaying leaves and dead organic matter, and there has been a lot of that recently,” he said.

The next likely insect to take flight in explosive numbers this spring is currently chewing contentedly on vegetation from Borrego Springs and Ramona to Torrey Pines and Chula Vista. Thousands upon thousands of distinctive, green caterpillars will soon turn into white-lined sphinx moths. These moths will be most prevalent in the Anza-Borrego Desert State Park, where the wildflower bloom this year has been particularly impressive. But they’re also likely to swarm out closer to the coast.

These moths have been known to show up prolifically after notably wet winters. Conlan said Anza-Borrego visitors may get an up-close look at this species.

“It can be very common to the point where they’re crisscrossing the roads in huge numbers,” he said.

No one has contracted Zika virus from a mosquito in California, but hundreds of residents have been infected in other countries and then returned to the state.

Arthur Shapiro, a professor of evolution and ecology at UC Davis, said in most years, the white-lined sphinx moth migrates northward into California’s central valley and eventually passes over the Sierra Nevada mountains to feast on monsoonal desert plants in July. This year, he said, it’s unclear whether that pattern will happen. The Yolo Bypass, a flood-diversion channel between Davis and Sacramento that’s usually dry and full of plants that the moths like to eat, is covered by 19 feet of water at the moment.

“If the white-lined sphinx does make it up here, I don’t know where they’ll breed,” Shapiro said.

Ironically, the situation could end up helping out the Central California butterfly population in mid- to late summer. After water in the bypass eventually recedes, many butterfly species might very well swarm in and lay their eggs in areas that have been under water and are now devoid of natural predators, Shapiro noted.

“From July through October, the numbers can be incredible in areas like this that have been under water during the spring. It restarts the system, takes things back to zero and lets everything redevelop,” he said.

Another species marked by metamorphosis, the painted lady butterfly, generally shows up in massive numbers during wet years. It starts as caterpillars munching on desert plants in the late winter and then following vegetation blooms all the way up the state, sometimes reaching Oregon.

Both Conlan and Wall forecast a major showing of these butterflies in the coming months for San Diego County and beyond.

Shapiro said the moisture-laden winter of 2005 produced a writhing mass of painted lady caterpillars that quickly turned into swarms of butterflies moving northwest from the state’s southern deserts to the verdant, blooming fields in the central valley.

“You can’t believe the numbers that were involved in 2005. They were so thick that they were disrupting traffic,” Shapiro said.

Elevation also plays a role in the springtime behavior of butterflies.

Many species, such as the highly migratory California Tortoise Shell Butterfly, are greatly dependent on winter conditions in the mountains. While drought years, including 2016, generally lead to smaller populations of these species, a thick insulating blanket of snow tends to help more of the butterfly pupae survive through the coldest months and then emerge when the snow melts.

Because the snowpack in California’s mountains is extremely thick this year, Shapiro predicts a late butterfly season in those elevations. So will there be swarms of butterflies in mountain meadows this summer? That’s hard for Shapiro to foresee.

“We’re waiting with bated breath to see what happens when all that snow finally melts,” Shapiro said.

Because the current profusion of vegetation has enabled a lot of caterpillars to find food at lower elevations, Wall said he also expects to find an increase in the population of Calosoma beetles — which are often called caterpillar hunters due to their eating habits.

Termites are another insect group that should have a markedly bigger presence this year, Shapiro said. Significant increases in soil moisture can help termite populations expand for up to three consecutive years.

“It should be a great year to be a termite exterminator,” Shapiro said.

In terms of the human health aspects of a super buggy 2017, mosquitoes pose the greatest concern to medical and vector-control experts.

Conlan said mosquitoes usually don’t begin appearing until May, when the weather warms up, and the Aedes aegypti variant that transmits Zika is not prevalent until August. The various kinds of Aedes mosquitoes also can spread dengue fever, chikungunya virus and yellow fever.

The county government’s vector-control crews are already dosing large bodies of standing water with larvicide pellets that can keep mosquito larvae from becoming droves of the blood-sucking insects. These workers are having to visit more places because some sites that had dried out from prolonged drought are suddenly in play again, holding moisture for the first time in years.

For instance, Lake Hodges in Escondido and the eastern reaches of Los Peñasquitos Lagoon east of the Torrey Pines Reserve are receiving repeated scrutiny. So is Lake Rancho Viejo, a small body of water at the center of a community just east of Interstate 15 and south of Highway 76 near Fallbrook.

Lake Rancho Viejo “hadn’t had water for probably two years, and now it has come back onto our radar screen,” Conlan said. “It will probably end up getting treated by air when we start up our aerial drop program in about a month.”

Currently, there are 48 locations listed on the county’s aerial larvicide application schedule, which the public can view at bit.ly/aerialdrop.

Last summer, county crews also started conducting comprehensive neighborhood spraying operations because Aedes mosquitoes were detected near the homes of patients who tested positive for Zika virus after traveling abroad. The spraying is intended to keep the virus from moving into the local mosquito population, which would significantly elevate the threat of Zika infections to all local residents — and especially pregnant women, whose babies are at risk of suffering a devastating brain defect called microcephaly.

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