This summer monsoonal rainfall event of 1.5 inches (about 40 mm) occurred overnight on Thursday, August 4, 2016.

Many different ant species of the desert southwest exhibit an interesting mass swarming behavior immediately after a soaking rainfall in the summer monsoon season. The ants await a reasonably generous rainfall (usually about a half inch/13 mm or more) hidden down in the depths of their colony, which has numerous chambers running many feet deep into the soil. These chambers hold both male drones and female virgin queens, in addition to the normal worker ants, the brood pupae, and the dominant colony queen who lays the eggs.

This photo was taken at sunrise on Thursday August 4, 2016 after an overnight thunderstorm complex dropped 1.5″ of rain on me, triggering this mass emergence of ants to breed in what is called a nuptial flight.

Upon sensing a heavy summer rain, especially after a prolonged dry spell, the waiting drones and virgin queens emerge en masse by the hundreds or thousands and swarm on the soil surface, on objects near the colony, and in the air about 10 to 20 feet above the nest. The purpose of this is an orgy of reproduction, in which the males and females couple up, exchange genetics, and then the no-longer-virgin queens fly off to start new colonies elsewhere. The males die almost immediately after mating, having served their more or less sole purpose in life as a short-lived stud, described by famous ant biologist E.O. Wilson as a “single-purpose sexual missile” whose sexual organs literally explode into the genital chamber of the queen. What a way to live and die, dudes!

A virgin queen mating with a darker drone. I am not sure of what species of ant this is, but I believe these might be leafcutter ants, Acromyrmex versicolor. (They might also be harvester ants, Pogonomyrmex sp.) Please correct me if this is wrong in a comment below.

The newly-fertilized queens then disperse, shed their wings, and attempt to start a new colony elsewhere. Most will fail, although obviously some do succeed in order to perpetuate the species. The rain-softened soil enables the new queens to dig their initial chamber more easily, since they do not have help from their worker offspring yet. Plus the important environmental cue of the rainfall enables other local colonies of the same species to synchronize their swarming too, which ensures genetic outcrossing that prevents inbreeding. Mass emergence also gluts the market for various predators such as lizards, birds, bats, and other ant species that treat the defenseless new queens (and their stored body fat, required for egg production in the new colony) as a handy and nutrient-rich food source. This behavior is also found in termites and some bee species.

I’ve stood outside at both sunrise and sunset just after a drenching rain in the late afternoon and watched the show of emerging ants, and the swooping bats and nighthawks that feed upon them. There’s something so vital about witnessing nature conduct these sorts of displays, whether it is a field of wildflowers, a herd of migrating wildebeests, spawning salmon, or swarming ants after a long dry spell ends. Every one of these scenes is about the struggle for survival and the need to carry on the species. And there’s beauty in all of it.

These ants were engaged in their nuptial flight about 10 to 20 feet above my car, which seemed to attract them.

As males and females paired off, many of them settled to the ground, with some of them landing upon the roof of my car. They were gone within an hour or two, dispersing out into the desert to find new places to set up colonies.

Dozens of pairs of no-longer-virgin ant queens and drones congregate on the rain-dampened roof of my vehicle. Others copulated upon the ground, nearby rocks, or vegetation. A busy Thursday morning at the “Ant Disco Bar”.

Wandering around, I came across a half dozen or so of these nuptial flight ant swarms. This event occurs only once or twice a year so it’s not that easy to see, although it is somewhat predictable at least in that it usually occurs right after the first good rain of the summer monsoon around here. So whenever that happens, it’s a good bet to go looking for nuptial flights shortly after the rain ends if you want to see for yourself.

This is a view of the rain-soaked southeastern Mojave Desert across my property and beyond, with the Black Mountains of northwestern Arizona visible in the far distance. I was taking this photo to show the view across the Joshua tree-forested landscape at the time. It was only upon enlarging and editing this photo that I noticed the presence of another nuptial flight swarm in the upper left corner, speckled against the overcast early morning sky. On my walk I would come across at least 20 to 25 of these swarms, not just the one I photographed near my house and atop my car.

The overnight rains were heavy enough to cause significant runoff, which filled both of my flood retention basins to a depth of about 4 feet (1.2 meters). I excavated these basins in July 2008 in order to capture, retain, and percolate this floodwater into the aquifer that my well shaft relies upon to provide my household, nursery, and gardens with water. The well shaft can be seen in the middle left distance. The pole in the right foreground is a depth gauge. The water has already soaked in almost 18 inches (45 cm), as indicated by the debris line ringing the basin, which at maximum depth was nearly merged with the other basin in the distance. This is all water that will replenish whatever I utilize to run my home and business during dry spells. I probably add significantly more water to the aquifer than I withdraw at this point.

The well shaft sits in shallow water for a few hours before it drains into the sandy soil and ultimately down to the aquifer. At full pool, the twin basins together retain somewhere around 100,000 gallons (400,000 liters) of water. Most rainfall events do not produce enough runoff to fill both basins fully, but even partial fillings yield important quantities of recharge water. The well pump is operated via solar power, which provides all of my domestic electrical needs off-grid.

Continuing my post-rainfall early morning stroll, I came across numerous additional nuptial swarms engaged in their mating frenzies across the desert. Virtually every mature ant colony of several species was waiting for the right quantity and timing of rainfall to conduct this mass emergence.

Swarms appear to be attracted to large, dark objects and hover above and land upon them as they conduct their breeding activities. I witnessed swarms above my house roof, my car, large rocks, and dead Joshua trees like the one above. I don’t know why ants exhibit this apparent preference. It is a short-lived phenomenon, as the ants disperse within only an hour or two to set up new colonies while the soil remains moist. Time is of the essence, since the hot drying desert sun can return within a day or two, making excavation of new nests in rain-damp soil for the solitary queens much more difficult. Most of these freshly-minted queens will fail to establish new colonies, but enough do that the species goes on.

As I wandered about, I took various photos of the landscape and low cloud formations, since low hanging clouds are quite rare in the Mojave/Sonoran desert transition zone where I live. And again, I ended up inadvertently capturing distant nuptial swarms with my telephoto zoom lens. I did not know these airborne ant swarms were present at the time I took these photos, and I find it rather fascinating that I got so many in my photos without any intention to do so.

Much to my surprise, fog rolled in across the landscape. This is much rarer than low-hanging clouds and occurs at most once or twice a year, often less than once a year. This view is of my property from across Alamo Road looking to the west.

How cool! I’ve literally only seen this happen a handful of times in nearly 20 years here.

My house and desert gardens, about to be enveloped in a rare fog bank on Thursday August 4, 2016. This can happen during the summer monsoon season, or during the winter with the passage of Pacific frontal storms, but is very uncommon at either time of year.

A view of the entry drive and some of the gardens at D:F Ranch underneath a low fog bank hovering just barely above ground level. The house is in the distance to the right.

Below, a selection of photos of the ranch surroundings and desert gardens during the passage of the fog and the subsequent clearing. The misty phase was brief, lasting perhaps 15 to 20 minutes, which follows the usual pattern for this region. The sun returned later in the morning, as one would expect for an interior desert biome. But it was pleasant while it lasted.

Lastly, I found this scene of a California juniper tree (Juniperus californica) near my house with a spread of recently-fallen “berries” – actually fleshy cones, as this is a coniferous tree – strewn evenly beneath the canopy. I just figured I’d post a few photos of the powdery blue berries and damp, color-saturated chestnut-reddish needles for artistry’s sake.

Desert rains activate the human sense of beauty as much as they activate the biological impulses of ants and plants. It’s always a pleasure to bear witness to.