It’s (still) Monarch season!


Monarchs basking in the sunlight

I’ve been meaning to write this post for a while but even so I’ve managed to get it done before Monarch season ends. Mainly because, at least in southern California, it’s always Monarch season!

Monarchs have been in the news a lot lately. Researchers have proposed the Monarch for consideration for formal protection as a Threatened or Endangered species. The US Fish and Wildlife Service will consider the proposal, listen to commentary from the public, and eventually make a decision, but that process will likely take a while. The argument for putting the Monarch on this list is mainly based on the fact that overwintering habitat has declined, fewer butterflies are showing up at these overwinter sites than in past years, and habitat along their migratory corridor is being lost to human development.

To understand all of this it’s important to understand how different Monarch biology is from that of most butterfly species. North American Monarchs can live as far north as southern Canada. In the fall they start to fly southward, most likely responding to temperature and daylight cues as well as cues sensed as their host plants, native species of milkweed, start to dry up and die back. Populations of Monarchs east of the Rocky Mountains generally fly south to spend the winter in Mexico, while those west of the Rockies usually make their way to the central and southern California coast.   When they get to their overwintering spot they congregate in huge numbers- millions at a time- and roost together in clusters along the trees. I’ve never been to the overwintering colonies in Mexico but I’ve heard that if you fly over in a plane, the trees below appear orange from all of the Monarchs hanging off of them.


A docent talks to the crowd about Monarch butterflies in Pacific Grove, California

In Pacific Grove on the central coast of California you can visit one of these overwintering sites between October and February. It’s hard to estimate how many butterflies spend the winter here, but it’s easily high into the tens of thousands. Last month we were lucky enough to visit this amazing place and see this awe-inspring natural history spectacle up close. The site itself is great- it’s easy to get to and a docent on duty will answer questions, make sure nobody harms the insects, and give talks about the butterflies’ biology to the public who come to view the phenomenon. You can buy butterfly-themed gifts and gadgets from a cart at the park, and all of the proceeds go to butterfly protection.


In Pacific Grove on the central California coast, thousands of Monarch butterflies cling together for protection on a winter day.

On the day we were there it was sunny and mild, and quite a few of the butterflies had warmed up enough to take short flights around the area. A few of them sauntered out looking for nectar plants, several were coupling despite the fact that successful matings are rare during overwintering, but the vast majority of them were hanging in clusters off of the trees. I had heard about and seen pictures of these clusters for years but seeing them in person was a completely different experience. It was incredible to see just how thick these groups were- layers and layers and layers of animals all clinging together for protection and warmth.

In another month or so these animals will start to disperse from their winter habitat and move northward. Generation by generation they’ll repopulate the US and southern Canada through the spring and summer, until the days grow short again next fall.


You can buy Monarch-themed clothes, toys, and other items, all for a good cause.


Enemies in the Garden

So you’ve created the perfect butterfly garden.  You’ve got nectar available spring through fall (or winter if you live in a warm climate!).  You’ve planted your garden with lots of native species that are attractive butterfly host plants, and included vertical, textured surfaces for the pupae you hope will soon populate your garden.  Sounds like butterfly paradise, right?

Not necessarily.  Butterflies have a lot of natural enemies, and they suffer a lot of mortality at every single life stage.  This makes sense- a female butterfly might lay between 20 and 100 eggs in her lifetime.  If they all survived to adulthood we’d be overrun  (this might not be that bad, actually…). Predators, diseases, and parasites are all part of a natural, healthy ecosystem.  It’s how nature keeps population size in check.  In the case of butterflies we typically think of the threat from predators like birds, spiders, or lizards.  But chances are good that mortality at other life stages actually plays a more significant role in the survival of most butterfly species.

Eggs are tiny, inconspicuous, and fragile.  They can easily be trampled by larger animals, eaten inadvertently by larger herbivores, or succumb to fungal infections.  Caterpillars can be eaten by predators, become infected by fungus or pathogens, drown, dry out, or become infected by parasitoids.  Pupae can be knocked loose from their hold, be crushed, or succumb to fungus, pathogens, or parasites.  Animals at all life stages can be destroyed by severe weather, including heat, cold, sun, rain, wind, or other abiotic forces like fires.

Out of all of these threats, the one I personally find the most fascinating is the threat posed by parasitoids.  Like a parasite, a parasitoid spends a significant portion of its life cycle living inside or attached to the body of another organism.  Parasitoids, however, typically consume and kill their host.  Charles Darwin found the existence of parasitoid wasps so troubling that he once wrote in a letter that “I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars.”  His concern was justified- many parasitoids are notorious for consuming their living host from the inside out, rendering the host organism little more than a zombie incubator for its parasitoid master. In many cases they start by consuming the non-essential organs so that the host lives as long as possible, only progressing to the essential organs when they are just about to emerge.   Once the parasitoid is finished growing it detaches (if it’s external) or burrows out (if it’s internal) from the host body and continues on its merry way, ready to mate and find a new host for its eggs.

Parasitoid species are many and varied, and they attack many other organisms besides butterflies.  Read about a cool parasitoid wasp that targets the Hemiptera, or true bugs here!


Travelogue: The Sky Islands of southeastern Arizona

In just a few weeks I’ll be moving from Prescott, Arizona to the Santa Monica Mountains in Malibu, California. I’m looking forward to the move but there are a few things I will miss about living here. One of the things I’ll miss the most is the opportunity to travel to the Sky Islands in the southeastern corner of the state. This is one of the most biologically interesting areas in the country, and one of the best places for butterfly diversity. Each of the isolated mountain ranges houses a slightly different inventory of butterfly species but all of them boast a wonderful checklist of species that are normally found only in Mexico. For a butterflier, this is a bucket-list destination. I’ve only lived in Arizona for two years but have managed a few trips to the Sky Islands. Each trip has been memorable.

On these trips we’ve visited several different areas that are famous for their butterflying opportunities. If you plan on visiting the area, and invaluable resource is Bailowitz and Brodkin’s Finding Butterflies in Arizona:  A Guide to the Best Sites. Be aware that fires have damaged some of the places mentioned in the book, so things aren’t always as described. Still, it has great information on what to expect at various localities, how to access the different regions, and the amenities present at each. We’ve used the information in this wonderful guidebook while exploring Madera Canyon and its nearby environs, Sycamore Canyon (one of my favorite places on earth), Mt. Lemmon, Patagonia, and the Huachucas. On this, our most recent trip, we went to several of these places and weren’t disappointed. But for this post I’m going to focus on one of the most famous ranges, the Chiricahuas.

But first, a quick explanation because by now, the uninitiated among you are probably wondering what the Sky Islands are, exactly. Sky islands are isolated mountain ranges, each surrounded by distinct lowlands, and each potentially housing endemics (species or subspecies that are unique to an area), and/or relics (an organism that used to be widespread but is now confined to a narrow distribution). Sky islands often house a great deal of biodiversity, and have become targets of conservation efforts as we humans expand our reach across more and more of the planet. Sky islands are predicted to become even more important as climate change begins to impact species’ ranges- species confined to mountaintops may not be able to withstand changing climatic conditions, while other species may begin to move upslope.

We arrived at the Portal entrance on the east side of the Chiricahuas in mid-afternoon and decided to head to the American Museum of Natural History’s Southwestern Research Station. The SWRS has a long and venerable history of hosting biologists and other researchers who study this remarkable place. It also hosts numerous courses and workshops throughout the year where students, scientists, and other interested folks can spend some time learning about a specific topic. During our visit the SWRS was hosting an ant course.  On a hunch I inquired as to whether Terry McGlynn, who blogs over at Small Pond Science, might be there.  I was pleased to find that he was, and I delayed his lunch briefly to introduce myself and make plans to get in touch when we move to LA.

The SWRS allows visitors on part of the grounds. The main draws are the hummingbird feeders and the butterfly garden. As a former birder married to a birder, I enjoyed spending some time watching the hummers battle it out at the numerous nectar sources available. The most exciting species while we were there were the blue-throated hummingbird . These suckers are large, showy, and incredibly aggressive. Most hummingbird species are fairly territorial and aggressive, actually, but these animals were particularly unwilling to share their resources, despite, in this case, numerous feeders as well as nectar-producing flowers.

The hummingbird feeders are the main attraction for most folks, but I, of course, was more interested in checking out the visitors to the butterfly garden. During our trip the main nectar sources appeared to be verbena and milkweed. Lots and lots and lots of Northern Cloudywings, Thorybes pylades,  were taking advantage of the blooms. I checked as many of them as I could to see if any of them were actually Valeriana Skippers, Hammock Skippers, or any of the longwing skippers, but no dice. All of the large, dark skippers make up a challenging group. Most non-butterfliers would probably assume, based on their relatively drab coloration, that they are not butterflies but rather moths. This is actually true of a lot of skippers, not just the large, dark spreadwing group. Skippers are an acquired taste, but for the butterfly enthusiast, few things pose a more enjoyable challenge to ID.

Two other potentially challenging species were making an appearance at the garden that day- Monarchs and Queens. Both species lay eggs on milkweed, and the caterpillars feed on the foliage as they develop. They are able to take advantage of the milkweed’s toxicity, sequestering the cardiac glycosides into their bodies without harm. This provides them with a chemical defense against predators. The Queen and the Monarch are Müllerian mimics (more on mimicry later!), warning predators of their toxicity through a bright color signal (aposematism). Because both species are giving an honest signal, warning predators not to eat them, when they can coexist in the same area they’re actually helping each other out- the two species look so similar that if a bird (or other predator) eats a Queen, it will remember the bad taste, associate it with the color pattern, and avoid both Queens and Monarchs in the future. The same is true if it encounters a Monarch first. During our visit we saw several adults of both species, as well as several large (late-instar) Monarch caterpillars busy munching milkweed.

In 2010 a human-caused wildifire, the Horseshoe Fire swept through part of the Chiricahuas southwest of Portal. The fire destroyed several thousand acres of this beautiful area and cost millions of dollars in damage. Then, in 2011, tragedy struck again. The Horseshoe 2 Fire began in early May and wasn’t completely contained until late June. Over 220,000 acres burned during this fire, costing well over $100 million in damages. Dozens of buildings, including homes and businesses, were destroyed. This fire, too, was human-caused. The ecological impact to the range is still being assessed, and it will most likely be many years before the full extent of the damage is understood.

Should you ever decide to take a trip to the Sky Islands you won’t be disappointed.  The monsoon season, late summer, is my favorite time to go.  Not only does the vegetation start to turn lush, but Madrean butterflies and birds move north with the rains, coming up from Mexico and giving the observant butterflier quite the treat.  There is lodging available in most of the ranges, but camping is easy to do there as well.  Don’t let the heat scare you- the monsoon season is one of the best times to visit Arizona.

Butterfly Gardening for Babies, Children, and Teenagers

This is a follow-up post to Butterfly Gardening for Adults.

So you’ve planted nectar flowers and attracted lots of adult butterflies to your yard, and now you want to see if you can add species diversity.  Or, perhaps you want to observe these beautiful insects during any or all of their other 3 life stages.  With just a little bit of effort you can rear a butterfly from an egg to an adult, right in your yard.

An adult female butterfly has one main motivation:  find the correct plant and lay her eggs.  What do I mean by “the correct plant”?  It turns out that most species of butterflies are picky about where they’ll lay their eggs.  Monarchs famously lay their eggs on milkweed (Asclepias spp.), but most other species would find milkweed to be just as toxic and unpalatable as  you and I would.  If a monarch female laid her eggs on the foliage of a rose bush, her children would find the leaves inedible and they would starve to death.  Because of this, butterflies (and people who study them!) need to be good botanists.  Lepidopterists (scientists who focus their studies on moths and butterflies) often work with botanists, native plant societies, chemists, and others to try to understand how a butterfly decides where to lay her eggs.  These plants are referred to as host plants, and they are a critical component of the butterfly life cycle.

A Colorado Hairstreak, Hypaurotis crysalus, on its hostplant, Gambel Oak, Quercus gambelii

A Colorado Hairstreak, Hypaurotis crysalus, on its hostplant, Gambel Oak, Quercus gambelii

Why would the Monarch caterpillars starve to death if their mother deposits her eggs on the wrong plant?  Because plants produce chemicals (called phytochemicals) that give them color, produce fragrance, help carry out physiological processes, and defend them against enemies.  Enemies of plants include fungi, bacteria & viruses, and herbivores (animals that eat plants).  Butterfly caterpillars are herbivores.  If they’re present in large enough numbers they can strip the leaves and stems from a plant, weakening or even killing it.  Because of this, many plants have evolved the ability to produce defensive chemicals to reduce the likelihood that they’ll fall victim to herbivores.  But, just like in an arms race, some herbivores have managed to overcome these defenses and exploit the plant in question as a food source.  The milkweed- Monarch example is a great illustration of this.  Milkweeds produce chemicals that are toxic to most herbivores (including humans), but the monarch has evolved the ability to ingest milkweed foliage without incurring damage from those chemicals.  Monarch mothers can lay their eggs where very few other insects can, and her children will thrive.

So how do you decide which host plants to include in your garden?  You can start by researching the host plants used by the adults that come to your garden.  Butterfly field guides almost always include information on the host plant used by each species.    If you want to attract new species to your garden, these same sources can help with that, too.  Look to see which species you can expect in your area, paying close attention to the habitat type (e.g. if you live in a sage desert, you’re not going to get marshland species in your yard!) as well as to the geographic distribution.  eButterfly is a great way to track what shows up in your yard as well as to see what species are showing up nearby.  You can also keep an eye on wildflower gardens and nurseries in your neighborhood to see what other species of butterflies are around.

Once the eggs hatch out, the caterpillars will be very hungry.  While a few species tend to lay

Pipevine Swallowtail larva, Battus philenor, on its host plant Aristolochia

eggs on one host plant but spend their time as caterpillars on another, most  stay on the same species for both life stages.  For this reason you can usually accommodate eggs and caterpillars of a given species with the same plant.  Be aware, though, that caterpillars can have voracious appetites.  Very few butterfly species are considered to be crop pests in the US (a notable exception is the Cabbage White, Pieris rapae), but they can seriously defoliate your plants, nevertheless.  If you have a vegetable garden, be aware that you may lose some things to caterpillars if you don’t find a way to discourage them.  This is mainly true of crucifers and legumes, which serve as host plants to many species of sulphurs and whites.  Anise, citrus trees, alfalfa, blueberry and cranberry plants, gooseberry plants, rice, figs,guava, and cherries are some of the other plants that might unintentionally become host plants in your butterfly garden.  It’s unlikely that a colony of Giant Swallowtails, Papilio cresphontes, are going to seriously damage your lime trees, but a few Cabbage Whites can put a hurting on the mustards in your salad garden.

Caterpillars go through several molts, growing larger each time.  We call these instars– after hatching from the egg, the caterpillar is in its first instar; after the first molt, it is in its second instar; etc.  The number of larval instars varies from species to species but averages ~5.  Once the caterpillar enters its final instar it will prepare for the pupal stage, also called the chrysalis.  The caterpillar will prepare to pupate by crawling to a place that is (hopefully) safe from environmental extremes, predators, parasitoids, and has a good substrate for attachment.  This might be its host plant, but is often a textured vertical rock face, a tree trunk, or, in a garden, a fence post or flower pot.  The caterpillar will attach herself to the surface she’s chosen and build a complex structure around herself.  She’ll then appear to go dormant for several weeks- several months, depending on species.  In reality, though, there’s a complex developmental process going on inside that pupal casing!  But that’s a post for another day.   To make sure you are providing a place for your caterpillars to pupate, include some vertical surfaces like decorative rocks or fenceposts, and experiment with giving them a little shelter- a small overhang or roof can help protect the pupae from the weather.  Once development is complete, the adult butterfly will emerge and the cycle starts anew.

Next time:  Enemies in the Garden

Butterfly Gardening for Adults

Part I- attracting adult butterflies to your yard.

When leading butterfly walks or giving talks about butterfly watching, some of the most common questions that I get pertain to butterfly gardening.  Planting a butterfly garden is a great way to expand your butterfly-watching opportunities, brighten up and add value to your home, and provide essential habitat for butterflies in your corner of the world.  A butterfly garden can be as simple as adding a potted plant to the balcony of your apartment.

Before going into the details of what to plant, it’s important to note a very strict rule if you want your butterfly garden to be successful- no pesticides!  Insecticides don’t discriminate.  They’ll just as easily kill a butterfly as they will cutworms and squash beetles.

A Variegated Fritillary, Euptoieta claudia, nectaring on thistle. Photo taken near Prescott, AZ by Zach Smith

When most people think of butterfly gardening, they think of showy flowering plants that will attract nectaring adult butterflies.  This is, of course, an important component of a butterfly garden, and it may be sufficient for your level of interest, the space you have available, or the resources you have to commit to your garden.  It’s also a great first step- plant some nectar flowers and see who shows up!  You may find after a while, though, that you want to observe butterflies during their other life stages, and this is where some knowledge of natural history comes in handy.

Butterflies have four developmental life stages (they’re holometabolous), so a well-rounded butterfly garden should accommodate eggs, larvae, pupae, and adults.  But one individual species might have completely different needs for each life stage, and the requirements of one species will often differ from the requirements of another.  How to accommodate all of those different needs?

Let’s start with the adult stage.  Many (but not all!) species of butterflies in the US come to flowers to sip nectar for energy.  Unlike hummingbirds and moths, butterflies need to perch in order to drink (which they do by unrolling their long, tongue-like proboscis).  They locate nectar sources visually and by chemical sensing (similar to our sense of smell).  Some colors are more attractive than others but there are no hard and fast rules.  The best strategy is to observe what’s happening in your area and see what flowers are attracting the locals.  Take a walk around your neighborhood, your favorite park for butterfly watching, and a few nurseries.  Try a variety of colors and sizes for the best chance to attract multiple species.  Try to plant so that you maximize the blooming season- rather than lots of flowers that all bloom at once, try to stagger plantings so that things flower in different seasons, ensuring a constant supply of available nectar.

The shape and structure of the flower determines who can pollinate it, and who will come to sip nectar (if the plant produces it- not all flowers make nectar).  In addition to a landing pad, appropriate scent, and attractive color, a butterfly needs to be able to reach the nectar with her proboscis.  This means the throat of a flower can’t be too deep or too shallow.  For example, a small butterfly like a roadside skipper can easily reach the nectar of a small flower like lantana, but would probably have trouble getting nectar out of the long spurs of a golden columbine.

Taxiles Skipper, Poanes taxiles, nectaring on thistle flower. Note the black proboscis extending into the flower.

I always recommend planting native species whenever possible.  Native plants provide habitat for many different animals, reduce the amount of watering and fertilizing you’ll need to do, and help lessen the chance of spreading pests and invasive species.  If you’re lucky there’s a native plant nursery in your area, but if not, there is bound to be a native plant society, nature center, or master gardener group that can give you some pointers on how to acquire native plants for your garden.  The Xerces Society has a lot of great resources to help you with this.

Some flowers, despite being attractive additions to a cut flower garden, are essentially useless to butterflies.  Unfortunately, roses, peonies, and a lot of cultivated showy flowers won’t do much to attract butterflies.  This doesn’t mean a butterfly garden can’t be beautiful and showy, though-  milkweeds, butterfly bush (Buddleja), lantana, coneflower, lavender, (single) zinnias, and Joe-Pye weed are just some of the reliable flowers that butterflies find irresistible.

Some butterfly species are attracted to things that are… less charming than flowers.  Rotten fruit is attractive to species like emperors, admirals, anglewings, and many others.  Try smearing some overripe bananas on trees or fenceposts in your yard and see what happens.  Newly-emereged males of some species are often attracted to damp patches of ground, where they suck minerals out of the moisture with their proboscis.  This activity, called puddling, is apparently so compelling that a butterfly might lose all sense of inhibition and let you catch it by hand!  Puddles, stream edges, and seeps often attract dozens of butterflies at a time, all mesmerized by the intoxicating minerals they’re busy slurping up.  Probably the least winning habit of nutrient-seeking butterflies, at least as far as human sensibilities are concerned, is the tendency to come to scat and carrion, again presumably for the salts and minerals.   Since I doubt very many people want to incorporate either of those particular delicacies into their garden, I’ll refrain from expanding on that particular topic.

Up next: Butterfly Gardening for early life stages


Heads or Tails?

Hairstreaks are a group of butterflies in the Family Lycaenidae.  In the US, hairstreaks are widespread but frequently go unnoticed because of their small size and often drab appearance.  When they are noticed, they’re commonly mistaken for moths.  Their fast, erratic flight lends to this confusion.  If you get the opportunity to observe a hairstreak closely, though, it’s worth the effort.


Colorado Hairstreak showing purple dorsal surface. Photo taken outside of Prescott, AZ by Zach Smith

Like all butterflies, hairstreaks are susceptible to predators unless they develop some type of strategy to reduce the likelihood of being noticed, caught, and eaten.  Birds, lizards, and other invertebrates like mantids and spiders are just some of the predators that butterflies have to be able to evade if they are going to survive long enough to pass on their genes.  Many hairstreaks show some degree of crypsis, or coloration that helps them to blend in with their backgrounds.  A few, like the Colorado Hairstreak Hypaurotis crysalus are cyrptic on the ventral surface (underside), but vibrantly colored on the dorsal surface (upperside).  This bright purple hue is most likely an adaptation to distract predators, although colorful signals like this can often be used to signal to other butterflies- potential mates, competitors for mates, or individuals of a different species.

Many hairstreaks, however, have gone beyond the standard cryptic coloration mechanisms to evade predators.  The trailing (back) edge of their hind wings exhibits a “false head“.  Typically this false head consists of some combination of eyespots and “hairs” or tails resembling antennae and/or legs.  The idea is that if a predator notices the hairstreak, its attention will be drawn to the false head and it will aim its attack there, because a successful attack on the head is more likely to incapacitate the butterfly than an attack on another part of the body.  Instead, the predator comes away with a mouthful of flimsy wing, which breaks off while the butterfly makes its escape.  Experimental evidence (link above, reference below) suggests that this adaptive strategy is successful in increasing survival in butterflies that have this trait.

Gray Hairstreak, Strymon melinus, showing beak marks on the hind wing.  Photo taken near Jerome, AZ by Zach Smith

Gray Hairstreak, Strymon melinus, showing beak marks on the hind wing. Photo taken near Jerome, AZ by Zach Smith

Colorado Hairstreak ventral surface showing eyespots and tails

Colorado Hairstreak ventral surface showing eyespots and tails

As if that isn’t cool enough, though, many hairstreaks have taken this deception even further.  Hairstreaks have a habit of perching with their wings closed, upside down, and rubbing the trailing edges of their hind wings together.  This subtle movement is enough to further direct the predator’s attention to the false head, and it strongly resembles the movements made by the butterfly’s head while she sips on flower nectar.

Keep your eyes open for hairstreaks the next time you’re outside. If you’re fortunate enough to see one, take the time to observe it while it perches and see if you get tricked by the false head!  Want to learn more about the research on false heads?  There are several great studies out there.  Here’s just one (linked above):

R. K. Robbins 1981.  The “False Head” Hypothesis:  Predation and Wing Pattern Variation of Lycaenid Butterflies. American Naturalist Vol. 118, No. 5 pp770-775