Excerpted from Butterflies of the Bay Area and (Slightly) Beyond: An Illustrated Guide, coming September 30, 2025.
Butterfly Migration
I remember living in the Richmond District of San Francisco along Golden Gate Park for a while, and there was a particular day when I was walking and noticed a butterfly flying above me. As I watched it, I saw another, and another, all blasting down Fulton Street. They seemed to be coming out of the park, then heading due west up the road. Another and another, all just going over the tops of cars and my own head. I looked around madly to connect with another human and to verify what I was seeing. It was a California tortoiseshell (Nymphalis californica) “movement”—an explosion of them popping out of their chrysalises after a few days of extended heat, and I was caught up in it, awestruck.
Migration of butterflies doesn’t seem to be as clear cut as those who do and those who don’t. For instance, a vast majority of the blue butterflies don’t fly much beyond where they were born. Many, like gray buckeyes (Junonia grisea), definitely move about within their range, but they aren’t true migrants like the painted ladies (Vanessa cardui) and the most famous traveler, the monarch (Danaus plexippus).
So why do butterflies migrate? California tortoiseshells are following the new flowers on plants that are edible in the early spring and then proceed upslope to higher elevations into summer. Then there is a slight reverse migration in the fall. Monarchs travel in search of warmer weather to overwinter in. Butterflies migrate for different reasons. One rarely sees the full picture of what’s going on because it might take a few generations to complete the journey.
Painted ladies emerge by the bazillions out of the southern realms of California. A great place to witness this is at Anza-Borrego Desert State Park. In the early spring, depending on the year, they can be seen flying in a north-northwesterly trajectory. This butterfly has different migratory patterns throughout the world.
King of all the butterfly migrations is that of the monarch. It is the supreme example of long-distance displacement. Four full generations make the complete journey with the first three having individuals that live up to three months and the final, overwintering generation living four to five. Those living on the western side of America move from basins in Eastern Washington and Idaho in a south-southwesterly direction down to approximately the San Diego area. The ones in the east famously move south along the Eastern Seaboard, round the gulf, and settle in the state of Michoacán in Mexico. Numbers fell to a historic low a few years back throughout its western migration, then rallied like thunder the next year, leading many to conclude that we still have so much to learn with this butterfly. A large group of people are dedicated to this most famous of phenomena.
When butterflies come into an area, they are referred to as immigrants, and when they leave the area they are called emigrants. Those butterflies I saw on the street that day were emigrating to the foothills of the High Sierra. It’s a complicated behavior that starts to become more clear after many years of watching.
Butterfly watching
If you have sunshine and flowers (and even better the two simultaneously), the odds are with you that you’ll see some butterflies. They are little solar panels and they need to be in the high fifties in temperature to really get going. I guess I would have to add a third thing for the ideal recipe—no wind. Butterflies seem to abhor the wind, which makes sense with all their patrolling and following scent trails of pheromones. When looking for butterflies on any windy day, check the leeward side of any hill and you’ll most assuredly find them sitting out of the wind. You may even find them in what we refer to as dappled sunlight—where the shade and sun create glades in a forest or in and out of rows of mature trees on a street. In these areas one might see tiger swallowtails, margined whites, and all of the commas (formerly anglewings). A whole handful of skippers: Common roadsides, arctics, and silverspotteds seem to prefer this habitat as well.
Cabbage whites in summer. Male has one dot on each of its forewings (left). Female has two dots on each of its forewings (right). (Illustration by Liam O’Brien)
If you get a little more advanced in your species identification, you develop the ability to “Rolodex” (for you youngsters that was a card index fixed on a wheel people usually had on their desks for phone numbers. Back in the olden days called the seventies.) each environment as you enter it. Say the hike starts in sun at a trailhead, so you think about those species that live only in the sun, then the trail enters full shade. A perfect example of this: One usually only sees a cabbage white (Pieris rapae) in full sun and almost never in the shade of a forest. Its counterpart, the margined white (Pieris napi), is a denizen of the forest and isn’t seen in the open sun. Coastal scrub, riparian corridors, rocky outcrops, and grassland all have for the most part their own community of butterflies.
It is sad how much healthy, native habitat our species has altered, but do you want to know an interesting fact? We’ve actually created butterfly habitat with roadcuts, agricultural field borders, trails, and disturbed areas. Disturbance is great for the generalists (butterflies that lay their eggs on many host plants) but not so good for the specifests, the species obliged to a single plant, which is usually a native. Fill your gardens with native plants, folks. The generalists will do fine on their own. Remember to look up. It may seem obvious to turn your head to the sky to see a butterfly, but in general people walk looking forward and at the ground before them. There is a whole slew of species up in the canopy of the trees you are either walking below or by. California sisters, mournful duskywings, and golden hairstreaks skip and glide between the oak leaves on a hot afternoon. Keep your eyes moving low, mid-shoulder, and high.
Two other known behaviors of butterflies work toward your advantage in finding them.
The first is the phenomenon of mudpuddling. Males (and sometimes females) need minerals, salts, nectar, and protein to sustain them while in flight. They also play into the male’s need to create a spermatophore packet to pass to the female while mating. Salts are primarily found in the mud. You’ll mostly see blues and swallowtails there, but other species as well in the early afternoon sitting on the banks of creeks or simply using a puddle to extract compounds from the mud. One can also see them on animal scat extracting minerals and proteins.
The second behavior is hill-topping. Many butterflies, but not all, are internally programmed to go to the nearest hilltop to find a mate. Without this it would be extremely rough to find one another. Why a hilltop? Why do humans go to a singles bar? It’s an excellent way to guarantee procreation for the next generation. It usually gets going about 3:00 p.m., but some species like the anise swallowtail (Papilio zelicaon) are known to start earlier. There are many more boys at a hilltop waiting for girls to fly by. Once you witness this activity on your own it will be difficult to unsee it on every hike with a hill you take from then on. It’s wonderful to see all the aerial maneuvering going on at a mountain summit while trying to tell them apart.
Many butterfly enthusiasts carry binoculars, and this is something you might want to consider purchasing. They’ve made quite a few advances in recent years in close-range binocs, and these most assuredly will help you zoom in on those crucial details. Personally I never got into the habit of carrying them, and they would be rendered useless if I tried now on account of my freakish right eyeball.
To successfully photograph a butterfly, start by remembering that an adult butterfly has the equivalent of ten thousand eyes in those compound optical structures. They are programmed just after emerging to dodge anything coming too close—they’ve got mates to find and babies to make. So what is my advice? Don’t act like a bird. No sudden movements. You will be shocked how close you can get to a butterfly if you move incredibly slow. Slower than what you think is slow. Take your record shot furthest away, then slowly move in for more. If you see the wings go up as you approach and you want that pretty dorsal shot, take a slow step back. (Think about it—wings up means the next movement for the butterfly is a downward exit thrust.) Normally when you take that step back, the butterfly relaxes and drops its wings. If it leaves, don’t chase it. If you stay still, nine times out of ten the butterfly returns right to where it was. As they age on the wing each day, they become easier to approach.
Reprinted with permission from Heyday Books (c) 2025. Available September 30, 2025.
