Emma Pelton

Instead of rearing—which is risky and unproven in helping monarchs—we should focus on more effective ways to conserve these glorious wild animals.

Many of us have been there: Finding a monarch caterpillar, collecting it in a jar, raising it on milkweed, and then waiting patiently for a butterfly to emerge and take flight. Helping a child (or an adult) learn about this captivating, up-close example of metamorphosis can be incredibly rewarding. Unlike many wild animals, monarchs are easily reared, so it is no wonder that bringing caterpillars into the classroom or home has been used by teachers and parents for decades as an educational tool—or just for the pure enjoyment of it. Rearing monarchs also has been a part of monarch research: From the tagging efforts started by the Urquharts in the 1960s to the multiple tagging programs of today. These programs, as well as other community science projects, have greatly expanded our understanding of migration paths.

A monarch caterpillar in the wild, on narrowleaf milkweed (Asclepias fascicularis). (Photo: Xerces Society / Stephanie McKnight)

Because rearing a butterfly in captivity enables people to share in the amazing transformation from a caterpillar to winged adult, it deserves a place in the future of monarch education and research efforts. However, we need to approach it thoughtfully and responsibly. Like any wild animal, we have to make sure that our interest in rearing monarchs does not harm the butterfly’s populations. This is particularly important today, with monarch populations down by 80-97%. These levels are so low that the migratory phenomenon to Mexico and coastal California is at risk. In an attempt to help reverse the monarch’s population free-fall, many people are attempting to save the species by rearing and releasing monarchs on a large scale. There are, however, serious concerns about this approach.

One aspect of the issue is the practice of captive breeding. Captive breeding refers to the practice of keeping adult monarchs in captivity and creating a colony to produce hundreds or thousands of monarchs; some of these are retained for continued captive breeding. It is often a commercial enterprise, with monarchs released at weddings and other events. The Xerces Society and several other monarch researchers released a joint statement in 2015 outlining concerns with this practice. These concerns include the risk that rearing monarchs in captivity can promote an increase in parasites, which can then be spread to wild monarchs when they are released. Secondly, continuous rearing over multiple generations can dilute genetic diversity, and have adverse effects on wild populations. In addition, releasing captive-bred monarchs into the wild can interfere with research studies aimed at developing a better understanding of monarch movement.

Interestingly, a study of recoveries of tagged monarchs suggested that captive-bred monarchs have lower migration success compared to wild monarchs (Morris et al. 2015). This research suggests that captive-bred monarchs have lower fitness—a biologist’s way of saying that these butterflies are less able to survive—and thus don’t help the population as much as wild monarchs. There is broad agreement among the monarch scientific community that captive breeding and mass releases can introduce unnecessary risks to wild monarch populations.

In recent years, a second issue regarding rearing has emerged. In an attempt boost the population people are turning to large-scale captive rearing of wild-collected monarchs. Captive rearing is the practice of collecting eggs, caterpillars, or pupae (chrysalises) from the wild, raising them in captivity, and then releasing them. In recent years and months, we have received more and more reports of individuals and groups who are focused on collecting eggs and caterpillars from the wild, rearing them in their homes, and then releasing them. Newcomers to rearing find encouragement on online platforms and networks of people who are also rearing. With this support, it can understandably start to sound like a great idea to raise more and more “cats.”

The practice has now become so commonplace in some circles, however, that hundreds or even thousands of monarchs are reared and released by a single individual each year. Many individuals with good intentions adopt this practice under the assumption that they are helping monarchs by lowering the butterfly’s notoriously high predation and parasitism rates found in the wild, where less than 10% of eggs make it to adulthood. By that logic, the more monarchs they rear, the more monarchs will make it to Mexico or California come winter. On the surface, this sounds like a good thing, but if you dig a little deeper, you’ll see this practice does not match up with what we know about how to actually reverse the monarch’s decline. There are no studies or other compelling evidence that show that releasing captive reared monarchs boosts the population. And if, at the heart of it, we are really trying to help monarchs, then we need to carefully examine the risks of captive rearing.

The fittest monarchs, best able to survive the migration, breed in the wild. (Photo: Xerces Society / Sarah Foltz Jordan)

So, why doesn’t rearing help monarch populations?

One way to look at this is to consider population fitness: Monarchs evolved to have very high rates of predation and parasitism, so stepping in in the hope that a higher proportion of eggs make it to adulthood is not necessarily the best thing for the population as a whole. This can be a little counter-intuitive, but it’s really about valuing the entire population of wild, beautiful monarchs instead of focusing on individual butterflies. For example, hypothetically, let’s say you wild-collect 100 eggs and 90 of them make it to adulthood instead of the 10 that would have survived on their own in the wild. Maybe some of those 90 eggs wouldn’t have survived on their own because they’re not as “fit” (in the biological sense) and now their less-fit genes are out there in a population that’s already in trouble.

Another way of looking at it is resource limitation: Let’s say you release those 90 butterflies (instead of the 10 which would have survived). Is there enough milkweed for 90 butterflies’ eggs and caterpillars to eat? Or did you just unwittingly create a situation where there will be too many caterpillars with too little food? If so, the boost in numbers possible through rearing doesn’t carry over to the next generation, and could be problematic due to competition for limited resources between the resulting caterpillars. Unfortunately, this apparently is a common phenomenon—especially in urban areas. We repeatedly hear from people that monarchs have defoliated their milkweed and there’s nothing left for them to eat. Again, when looking at the scale of the whole population, this could pose a problem.

An additional concern is that during rearing monarchs are kept in densities far greater than typically occur in the wild, making them very prone to diseases and infections from pathogens like the protozoan parasite OE. Some people who rear are aware of OE, taking precautions to sanitize cages and test adults to make sure they are healthy, but in other situations the spread of disease is a serious problem. Learn more about OE on the Monarch Joint Venture website and through Project Monarch Health. In addition, there are many other pathogens that can make monarchs sick (and may increase in captive rearing situations) but aren’t as well studied as OE.

A monarch butterfly infected with Ophyrocystis elektroscirrha (OE) may not be able to eclose from its chrysalis, or may emerge with wings that cannot extend and flatten. (Photo: Dara Satterfield / Project Monarch Health)

But don’t we captive rear other endangered animals?

Too few animals is an issue with some critically imperiled species which only have a small number of remaining individuals. The California condor is a high-profile example of a species with a captive rearing program. This approach has also been adopted for some butterflies, including the island marble and Oregon silverspot butterflies. For these species, captive rearing programs are carefully designed and closely monitored. In fact, Xerces has worked with several partners on captive rearing of very rare butterflies—but this is done in carefully managed conditions and only after a lot of research and consideration of how rearing and releases will affect the entire population. In addition, remaining populations of these butterflies are far smaller than the monarch butterfly’s population. And rearing operations are just one part of a broader strategy that includes ensuring adequate habitat to support them after release.

Monarch populations have (thankfully!) not fallen so low that the conservation community is seriously considering coordinated captive rearing. Other wildlife populations that are facing as great, if not greater, declines as monarchs—such as Kirtland’s warblers, Karner blue butterflies or wolverines—are in trouble, yet we would not even think to turn to raising them in our homes to help them rebound. (Well, there are plenty of other deterrents to putting wolverines in your living room!) However, something about monarchs makes rearing seem like less of a leap. We are already so used to collecting and watching them develop in containers and cages, that it has been a natural extension for many folks to dial-up captive rearing as a solution to the monarch’s plight.

So, what can I do instead of rearing?

Arguably, the problem may not be that we have too few monarchs, but rather that the monarchs that are still wild don’t have enough of what they need. They don’t have enough breeding habitat (milkweed and nectar plants); they don’t have enough areas safe from pesticides; they don’t have enough intact overwintering habitat; they don’t have enough protection from severe storms and drought due to climate change; etc.

Instead of rearing—which is risky and unproven in helping monarchs—we should focus on more effective ways to conserve these glorious wild animals. Our tactics should address the reasons the species is in trouble to begin with. We can do this through taking action to protect natural habitat; to plant native milkweed and flowers; avoid pesticides; support wildlife-friendly, local, and organic agriculture; contribute to research efforts via community science; and organize ourselves to push for policy changes. These are more effective ways to expend our energies in monarch conservation than trying to rear the population back to health—which we do not know is possible and may spell trouble for an already at-risk species. For more information about ways to help monarchs, check out resources on the websites of the Xerces Society and the Monarch Joint Venture.

You should feel welcome to raise a caterpillar or two to teach your family about monarchs or to report to a community science project, but put the rest of your efforts into some other action to help monarchs. Let’s work together to ensure that rearing monarchs does not unintentionally harm this iconic species we are all trying to protect!

To ensure that monarchs will cluster for the winter in the future, we should be focusing efforts on protecting overwintering sites and breeding habitat. (Photo: Xerces Society / Candace Fallon)

Answers to a few frequently-asked-questions and answers about rearing

How can I rear monarchs responsibly?

Rear no more than ten monarchs per year (whether by a single individual or family). This is the same number recommended in the original petition to list the monarch under the Federal Endangered Species Act. Collect immature monarchs locally from the wild, heeding collection policies on public lands; never buy or ship monarchs. Raise monarchs individually and keep rearing containers clean between individuals by using a 20% bleach solution to avoid spreading diseases or mold. Provide sufficient milkweed including adding fresh milkweed daily. Keep rearing containers out of direct sunlight and provide a moist (not wet) paper towel or sponge to provide sufficient, not excessive, moisture. Release monarchs where they were collected and at appropriate times of year for your area. Check out Monarch Joint Venture’s newly updated handout, Rearing Monarchs: Why or Why Not? Participate in community science, including testing the monarchs you raise for OE, tracking parasitism rates, and/or tagging adults before release. OE: Project Monarch Health.

Parasitism rates: Monarch Larva Monitoring Program.

Tagging: There are many tagging programs, many of which are location-specific.

What if I am raising wild monarchs for tagging or other community science projects?

Raising wild monarchs for tagging and other community science research projects can be really rewarding and the data these projects generate are incredibly useful to researchers. For example, we have learned through tagging that butterflies in the Pacific Northwest consistently migrate to coastal California, while butterflies in the Southwest have been found migrating to both coastal California and central Mexico! If you are rearing monarchs for a community science project, raising a few more than ten monarchs collected from the wild may be justifiable—but it is not an excuse to raise one hundred monarchs. Raising large numbers of monarchs for community science projects carries many of the same risks as captive breeding or captive rearing in high numbers. Finding a balance between contributing valuable data without compromising the health of monarch populations is a goal most researchers share—and the goal of most monarch community science programs is to improve our understanding of monarchs in order to help conserve them! So, keep the numbers you captive rear for community science research reasonable and be sure to report your data.

Can I raise monarchs on tropical milkweed?

Tropical milkweed (Asclepias curassavica) and other evergreen, non-native milkweeds (for example, balloon plant [Gomphocarpus spp.]) are readily used by monarchs and frequently sold in nurseries. There are many concerns with these evergreen species, particularly in mild-climate areas such as the Gulf Coast states and southern and coastal California, but also in other areas where these plants can lead to a buildup of the protozoan parasite OE and interrupt migratory behavior in monarchs. For these reasons, it is best to remove these species and replace them with native milkweed if appropriate. Learn more about the issues in the Xerces blog “Tropical Milkweed—a No Grow?”