El Niño Rains Are Coming — What to Know About Termite Swarms Before They Start

For most of the year, a subterranean termite colony under a Southern California house gives no sign that it exists. Then the first real storm of the season rolls through, the sun comes back out a day or so later, and a hairline crack in the garage slab lets go of a cloud of winged termites all at once. They flutter toward the nearest window, shed their wings, and are mostly dead by evening. If you were at work, the only evidence is a little drift of papery wings on the sill. This winter is forecast to be a wet one, and the rain hasn't started yet, which makes right now the most useful time to think about it.

Seasonal forecasters expect a super El Niño to take shape this winter. In plain terms, that means unusually warm water in the tropical Pacific, which tends to push the winter storm track farther south than usual and tilts the odds toward a wetter season in Southern California.

"Tilts the odds" is the careful way to put it. El Niño doesn't lock in a soaking winter here, and strong El Niño years have underdelivered in Southern California before. Nobody can tell you today how many storms are coming, how much rain they'll bring, or when the first one will land. We certainly can't. We're a termite and pest control company, not a weather service.

What we can tell you is how subterranean termites behave when the rain does come, because that part is very consistent. If this winter turns out as wet as forecast, expect the pattern below to show up more often, and more visibly, than it does in a dry year.

Subterranean termites live in the soil. The colony sits underground and sends workers up through narrow mud tubes to reach the wood they feed on, which is why the first sign many people see is a pencil-width tube of dirt running up a foundation or a garage wall. Everything about this species depends on moisture. Workers dry out quickly in open air, and the colony needs damp soil to survive.

Swarmers are how a colony starts new colonies. Over the months before swarm season, an established colony raises a batch of winged reproductives, called alates, and holds them until conditions are right. For the western subterranean termite here, the right conditions usually mean a soaking rain followed by a warm, calm day. The rain softens the ground so a new pair can dig in and start a nest, and the humidity keeps the fragile swarmers from drying out during the few minutes they spend in the air.

So the colony waits. When conditions line up, the swarmers pour out of exit points in the soil, cracks in a slab, or gaps inside a wall, fly a short and clumsy distance, drop their wings, and pair off. Nearly all of them die within hours. The few pairs that land on damp soil near wood try to start over.

More rain doesn't create termites. The colonies under your street are already there, and they took years to get established. What a wet winter changes is the number of days when conditions are right for swarming, and the number of chances you get to notice. In a dry year, a colony might swarm once on a weekday afternoon when nobody is home. In a wet one, repeated storms mean repeated opportunities, and the season can stretch from the first storms well into spring.

Wet soil also makes life easier for the workers. Saturated ground along the foundation, especially where a gutter overflows or a sprinkler soaks the stucco, is exactly the environment they need to forage close to the house.

This is mainly a subterranean termite story. Drywood termites, the other common species here, live entirely inside the wood they eat. They don't need contact with soil and get the moisture they need from the wood itself, so rain has little to do with their timing. Drywood colonies tend to swarm on warm days in late summer and fall, whatever the forecast says.

That has a practical side. If you find winged termites at a window during a dry, warm stretch in September or October, drywood termites are the more likely suspect. If they show up the day after a storm, think subterranean. The two need very different treatment, so it is worth getting a sample identified rather than guessing.

Swarms are short, and most people miss the actual event. What they find is the aftermath. Once the wet weather starts, these are the things worth a second look.

If you catch a swarm in progress, don't do anything dramatic. The swarmers are not damaging anything. Put a few in a zip-top bag or press them onto clear tape, take a photo of where they were coming from, and write down the date. Vacuum up the rest. Then call someone who can identify them properly.

Flying ants swarm at similar times of year and get mistaken for termites constantly. The quick version: termites have straight antennae, a thick waist with no pinch, and four wings of equal length that extend well past the body. Ants have bent, elbowed antennae, a narrow pinched waist, and front wings noticeably longer than the back pair. Our swarmers vs. flying ants guide has pictures, which help more than any description.

A swarm is a colony announcing itself, but it's a late announcement. By the time a colony is mature enough to produce swarmers, it has usually been feeding for years, so waiting for the swarm to tell you it's there means letting the rainy season set your schedule.

An inspection in a dry month looks at the same house without the urgency. A licensed Branch 3 inspector can check the foundation, the garage, the subarea where there is one, and the wood around the house for mud tubes, damage, and the conditions that invite termites in the first place. If something is active, treatment can be planned on your timetable instead of in the middle of a wet week. If nothing is, you have a baseline, and you know which spots to watch once the rain starts.

Some houses deserve a closer look than others. Slab homes with cracks or expansion joints, older raised-foundation homes with wood close to the soil in the crawl space, additions where a new slab meets an old one, and anywhere planters or soil are built up against the stucco all give subterranean termites an easier way in. Having any of these doesn't mean you have termites. They're just the places a good inspection spends the most time.

A swarm inside the house is a strong sign that a colony is close, usually in or under the structure. It is not a sign that the house is about to fail. Termite damage builds slowly, and a swarm is a reason to get an inspection soon, not a reason to panic tonight.

A swarm outside, from a fence post, an old stump or a pile of lumber in the yard, is less direct. It tells you colonies are active nearby, which in most Southern California neighborhoods is true anyway. That doesn't by itself mean they're in your house, but the house does deserve a look, since the conditions that suit a colony in the fence often suit one in the framing.

The part that trips people up comes afterward, when things go quiet. The wings get vacuumed up, no new swarmers appear for weeks, and it's easy to decide the problem went away. It didn't. The colony that swarmed is the same colony it was the day before, and it keeps feeding whether anyone sees it or not. Our article on the seven signs of termites walks through the other evidence to look for.