How to Count Thousands of Monarch Butterflies

 Every year thousands of butterflies spend their winters in the California Central Coast. As of November 12 of this year, a group of Museum staff and volunteers counted 8,400 monarchs in the Pacific Grove monarch sanctuary. One question both staff and volunteers are often asked is, How do you count them all? It seems like an almost impossible task, however, hundreds of people throughout California spend time counting the monarchs at their different wintering sites every year.

If we were to capture and count every single monarch butterfly, it would take all day, and we would be disturbing the butterflies and their habitat. Instead, we use estimation. To count the monarchs, we follow the counting protocols that were not only taught our organization, but to anyone who wishes to help count the monarchs at any of the wintering sites from San Francisco to San Diego. The Xerces Society, an organization that promotes the protection and conservation of invertebrates, and California Polytechnic State University’s Monarch Alert program are two organizations that help train California volunteers.

So, how do we count? We look at the monarchs in small clusters. A cluster is a group of 3 or more monarchs that are grouped together. A cluster can be large, and it can be difficult to see the individual butterflies within a cluster without the help of binoculars or a scope. Clusters can range in size from 30, to a few hundred or even a thousand monarchs. We do not count every monarch in a cluster, as this would take too much time and lead to fatigue of the counter. Instead, we count a small section of that cluster and use it to estimate how many total monarchs are in a particular cluster.

Monarch Cluster

For example, if we were to count the cluster pictured above, here’s how we would go about it. It’s rather large, so we would count an area of 10 monarchs – which we’ve gone ahead and highlighted in red below.

Cluster 10 counted

After we’ve counted 10 individual monarchs, we look at how big of an area 10 monarchs takes up in that cluster.

cluster group of 10

Then we estimate how many times that group of 10 would fit throughout the rest of the cluster.

Cluster 30 groups of 10

For this cluster we estimated that our original group of 10 fits in this cluster a total of 30 times, which means we estimate there to be 300 monarchs in this particular cluster. Wow. That’s a lot of monarchs in one small area. We would then go and count the rest of the clusters found in the Sanctuary.

It still takes a while to count the monarchs this way. When you stop by the Sanctuary you’ll see there are lots of monarch clusters to count. Also, if you’ve been there on a warm afternoon, you’ve seen the monarchs flying around everywhere. There’s no way we can count the monarchs if they’re flying around, so counters have to get up early, and arrive at the Sanctuary just after sunrise, while the monarchs are still too cold to move.

It’s a lot of work, but it’s really rewarding to get to spend the early morning hours with the monarchs.

Unusual Varieties at This Year's Wildflower Show

Penstemon grinellii, var. scrohulariodes

Today opens the 52nd annual Wildflower Show at the Pacific Grove Museum of Natural History. By typically having close to 100 families and 600 varieties of wildflower on display, the show boasts being the largest in the western and northern hemispheres.

But this year is even more exceptional. Right now 704 wildflower taxa are on display. Ironically, it turns out that three relatively common plants are missing, because the volunteer collectors each assumed someone else had gotten them. (The flowers have been in the show probably 50 times before. By tomorrow, I’m sure they’ll be here again.)

The museum’s first Wildflower Show was organized by Director Emeritus, Vern Yadon. In 1961, he and a single associate collected over 250 wildflower species. After he retired, the Monterey Bay Chapter of the California Native Plant Society (CNPS) took on responsibility for the show.

In the days leading up to “wildflower weekend,” volunteers from the CNPS collect from throughout the entirety of Monterey County and neighboring San Benito County. According to the show’s organizer, Brain LaNeve, this year at least 25 CNPS members participated in collecting.

Once back at the museum, they classify and identify the wildflowers for display. This is no mean feat.

For their identification key, CNPS botanists use the single most comprehensive resource on California's amazingly diverse flora, The Jepson Manual. In January 2012, the Jepson Herbarium at U.C. Berkeley published a revised edition, which incorporated significant changes to about 57% of the plant families listed in the 1993 edition. DNA sequencing had revealed that some plants shared ancestry, even though they appeared unlike; while some plants, which appeared very similar, were actually unrelated.

This meant that many plants’ scientific names changed. (To see the name changes, follow this web link: And so, the CNPS members had to re-identify plants they had memorized over the decades. As the quip goes, “Common names change from place to place; scientific names change from time to time.” (Vern says that Edith Wharton coined the phrase. I’d like to find the original quotation.)

The photo with this blog post depicts  this year’s “Best of the Wildflower Show.” Its common name is Grinnell’s penstemon. Its scientific name is Penstemon grinellii, var. scrophulariodes. The flower’s former family name is Scrophularieacea; thanks to the Jepson revisions, now it’s Plantageinaceae.

This penstemon is usually a summer wildflower, so 2013 is one of few during which the flower has been collected in the spring. In fact, the presence of [typically] summer wildflowers helps explains the huge number of varieties this year. It will be interesting to see how next year’s weather patterns affect the 53rd annual Wildflower Show count.

Annie Holdren, Exhibitions Curator

Knowing a Collector Through Her Collection

Cabinet of "Sands from Around the World" in the MVSEVM exhibition

As suggested by William Davies King, the author of Collections of Nothing, collectors know the world through collecting--and the world knows collectors through their collections.

Ever since we mounted it in the MVSEVM exhibition, a vintage collection of sand has attracted lots of interest and questions. The collection features 714 numbered glass vials containing sand from around the world. Who collected and labeled all this sand, when, and why? A 1922 Curator’s Report states that the museum received “Mrs. Sutton’s complete collection of sands gathered from all parts of the world. These in an excellent case were donated by Mrs. Martha Anderson.” That’s all we know, but there is so much more we can infer….

Mrs. Sutton typed up a list of her numbered vials, matching each with the location it was collected. One of the entries (vial #95) has a date: “San Francisco Fairgrounds, 1894.” We can further infer that she resided in Pacific Grove, since over 40 vials come from Pacific Grove and neighboring areas on the Monterey Peninsula. Perhaps she was a member of the Pacific Coast Branch of the Chautauqua Literary and Scientific Circle (held in this town between 1880 and 1917), because vial #105 is from Chautauqua Lake, New York. Then again, perhaps a neighbor contributed the Chautauqua sand.

We can also infer something about Mrs. Sutton’s personality. She was careful. Not only did she maintain records of her sands, she also appears to have sorted and separated the minerals in the sands. For example, vial #140 contains only light blue sand grains from “Moss Beach, Pacific Grove.” My mental image is of her sitting at a table under a bright kerosene lamp, holding a magnifier in one hand and tweezers in the other.

Did she herself travel to all of the places from which the sand was collected? Probably not. Vial #365 is from “Sea of Japan, One Mile Deep.” And she labeled numerous sands from archaeological and historical sites around the world, such as Abu Simbel, Egypt, and railroad ground-breakings.

Mrs. Sutton appears to have had some knowledge of petrology, or at least one of her sand contributors did. Not only did she separate parent rocks’ minerals from the sands, she also labeled numerous sands with the names of the minerals contained: actinolite, quicksilver ore, chloride ore, ulexite.

One notable local sand didn’t make it into the collection. That’s the garnet sand found intermittently along the Big Sur coast. It wasn’t until 1919 that the state approved building a highway to connect Big Sur with the Monterey Peninsula, so it remained inaccessible (and unknown) during Mrs. Sutton’s sand-collecting time.

Today, if you’re interested in seeing cherry-red garnet sand grains, visit Andrew Molera State Park. Follow the Beach Trail to the ocean. The sand appears as dark purple streaks near the mouth of the Big Sur River. For me, one big question remains, what and where is the parent rock of this garnet sand?

Coda: A little online research shows that Mrs. Sutton was born Angeline Robertson in 1830. Her father was a staunch Methodist. She married W. William Sutton, who was a member of the Masonic Association, a veteran of the Mexican War, and a member of the Sloat Monument Association. Mrs. Sutton was Grand Chaplain of the Eastern Star meeting in Pacific Grove in 1893 (a year before she collected sand from San Francisco). She died in 1915, and is buried with her husband in El Carmelo Cemetery, Pacific Grove.

Annie Holdren, Exhibitions Curator

Collection HIghlight - Doc Rickett's Squid

Dosidicus gigas; also known as Jumbo Humboldt Squid

Object Name: Dosidicus gigas; also known as Jumbo Humboldt Squid

About this object:

This squid came to the Museum by way of Ed Ricketts in 1935. Known for his pioneering work on intertidal ecology in Between Pacific Tides as well as his influence on John Steinbeck, Ricketts operated a marine biology supply house known as Pacific Biological Laboratories (PBL.) Among the few specimens that made their way from PBL to the Pacific Grove Museum of Natural History, this squid is the most notable.

Jumbo Humboldt squids live at depths up to 2300 ft and can grow up to 6 feet and weigh 100 lbs. They hunt in schools of as many as 1200 squids. This squid also changes its color to red when in an excited state, earning it the nickname “Red Devil.” They are known to be curious and intelligent animals.

Jumbo Humboldt squid inhabit the Pacific Ocean from northern California to southern Chile and are believed to have both small scale migration within the Gulf of California, from the Baja peninsula to Guaymas Basin. Humboldt squids were once only rarely spotted off of central California, but following El Nino events which warmed northern waters seemed to have expanded its range northward, being spotted as far North as Alaska.

Come see this spectacular specimen at the Museum. It is currently on display on the Museum’s mezzanine in the Mollusks display. Be sure and see the Museum’s newer specimen in the lobby, courtesy of Stanford Hopkins Marine Station. <Link to>


What vomiting jays have to do with monarchs and milkweed

Jays in the PGMNH "Monarchs Come Home" exhibition

Monarch butterflies

The end of February is the end of “monarch season” along California’s Central Coast. The monarch butterflies that overwintered in Pacific Grove and at other coastal sites are now mating and beginning to depart. The females are heading inland in search of milkweed, the plant on which they’ll lay their eggs. And the males? Well, since the females usually use sperm from the last male they mated with, it’s to the males’ advantage to move along with them.

Milkweed plants

Milkweed is the monarch butterflies’ host plant; it is the only plant that monarch caterpillars will eat. (Within the milkweed genus, Asclepias, there are about 140 different species.) As its name indicates, milkweed oozes milky-looking latex sap when it is cut open. This latex is the plant’s first defense against insects and other herbivores that might eat it. Latex is sticky and can gradually build up and harden in an insect’s mouth.

I’ve often wondered just how monarch caterpillars avoid the milkweed’s defenses. I learned the answer in Thomas Eisner’s book For Love of Insects. It turns out that the latex is stored under pressure in cellular tubes called lactifers, which follow the plant’s phloem and xylem (the veins that conduct nutrients and water). To feed on milkweed, a monarch caterpillar simply chews through a leaf’s midvein and doesn’t need to touch the lactifers. Cutting the midvein prevents the flow of latex to the tip of the leaf, so the caterpillar eats where latex no longer flows.

Besides latex, milkweed has other defenses. The plant also contains toxins (cardenolides) to prevent insects and other herbivores from eating it. But monarchs have co-evolved with their host plants, and they tolerate and utilize milkweed’s steroidal weaponry. They use the toxins against their own predators.

As they eat milkweed, monarch caterpillars incorporate its toxins into their own bodies. The caterpillars become toxic to the animals that would eat them. And this protection lasts through every stage of their life cycle.

Vomiting jays

 I can’t recall who wrote it (perhaps monarch biologist Lincoln Brower?), but this sentence has stayed with me: “The toxic dose is larger than the emetic dose.”It’s a dry way of saying: If a jay tries to eat a toxic monarch butterfly, the bird won’t die, but it will vomit. And then it’s likely to never try eating another orange-and-black butterfly again.

For our “Monarchs Come Home” exhibition, the museum had an avian taxidermist pose two scrub jays to mimic photos from a classic lab experiment run by Brower. Since this was the taxidermist’s first-ever request for a vomiting jay, he wasn’t quite sure how to re-create the ejecta. I suggested thread and hot glue. Visit the museum to see if you agree that it's convincing. And then let me know what you think.  

Annie Holdren, Exhibitions Curator


Our museum opened its doors in 1883. For 130 years this museum has been helping people explore and appreciate nature in the California Central Coast.

We started this blog to extend the conversations that we’re having within the museum walls out to our friends, colleagues, members, and anyone interested in nature and the California Central Coast. 

Meet our team…
  • I am the museum’s Executive Director and will showcase the critical importance of natural history today and the critical work of our partners.
  • Paul VandeCarr is the museum Collections Curator. Paul will be telling stories of uor collection. He’ll showcase items from the Museum’s collection of over 50,000 objects and tell the stories of the object’s donors and how the collection has grown over 130 years.
  • Annie Holdren, Ph.D. is the museum’s Exhibitions Curator and will provide deeper insights into our museum exhibitions and how they connect with the real places in the central coast.
  • Learn more about citizen science with Ann Wasser, the museum’s manager of the Long-Term Monitoring Program for Experiential Training for Students (LIMPETS).
  • As the museum’s Outreach Coordinator, Allison loves to promote science, nature, and culture through hands-on creative activities and events. 

Please join us as we share our interests in and passions for this incredible region that we live in.


Lori Mannel

Executive Director

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