island refuge

Usually we think of islands as delicate ecosystems, sensitive to change because of the few numbers of species there and their complex interactions that can be upset by the loss (extinction) or addition (invasion) of a species.  However, through the introduction of a couple of milkweed plant species, Maui, as well as Oahu and the big island of Hawaii, seem to have become a refuge for Monarch butterflies, whose populations are crashing in various parts of mainland North America.

In the town of Kapalua on the northwest shoreline of Maui, a very hilly and abandoned golf course has become a refuge for all sorts of exotic plants and animals like the Monarch butterfly.

It hardly seems possible that there could have been fairways and greens here once. A forest of Norfolk Island pines and other exotics have completely overgrown everything but the golf cart paths, which now make wonderful hiking trails.  That’s the island of Molokai in the distance.

These lofty Norfolk Island pine forests make welcome cool, shade on a hot, humid day.

Along the edge of the golf cart path, balloon milkweed, introduced from southeast Asia, grows in dense patches. Both flowers and seed pods were present, and dozens of Monarch butterflies flitted in and about the vegetation.

The flower head points downward (unlike other milkweeds) below reflexed petals, so the butterflies have to hang from the flower rather than perch on it. This might make it more likely they will catch their feet on the pollen sacs, removing them and helping the plant outcross its pollen to another plant.

A female Monarch butterfly feeding on the nectar of balloon milkweed attracted the attention of a few males, but fluttered her wings vigorously and drove them off.

Unlike Asclepias species of milkweed we have in North America, this species (Gomphocarpus phytocarpus) sports inflated pods surrounding the tender seeds within.  The air space between pod wall and seeds must make it difficult for seed predators to feed on the next season’s crop of milkweed plants.

Dozens of Monarchs flitted about us as we walked.  I don’t think I have seen this many Monarchs in an entire summer (or two) in Minnesota, but here they are thriving with plenty of the balloon milkweed leaves for the caterpillars to feed on and the nectar of this and other flowering plants in the overgrown golf course to sustain the adults.

It’s possible that Monarchs have become established on the Hawaiian islands by founding individuals from California, but that is a 2400 mile journey, and the wind generally blows from west to east, not the reverse.  Unlike the California population, island Monarch butterflies are not migratory, so once they have found isolated patches of milkweed, populations thrive and increase.  In addition, several butterfly “farmers” in Hawaii market their Monarchs for weddings, with additional individuals being released to the island as the couple pronounce their vows.

So here’s a rare story of how an introduced plant species benefits the survival of a species that is threatened in other parts of its range.  It’s a wonder how the butterflies find their milkweed hosts (needle in a haystack?), but impressive when they do.

Bugs in the garden

I haven’t seen any Monarch butterflies yet this year, and the milkweeds are just about to flower.  But the Milkweed Leaf Beetles are more abundant than ever.  They just love the pink-flowered swamp milkweed (Asclepias incarnata).  Last week I found adults crawling all over the tops of the plants near the unopened flowers (which they also devour in addition to the leaves).

These milkweed leaf specialists look a little like ladybird beetles but are much larger (about twice the size), and have larger black spots.

Males follow or ride on females as she munches on flowers or leaves. He guards the female from other potential suitors, until she lays a batch of eggs on the underside of the milkweed leaves.  Then he may wander off to find another female.  Both sexes may mate many times during their short summer lifespan, which ensures a lot of gene flow in a population.

After seeing adults in the garden for several days now, I examined the underside of the milkweed leaves this morning to see if there were any larvae present, and sure enough all stages of larval development were present.

A small clutch of milkweed leaf beetle eggs had just hatched (egg cases still remaining).  This is the first of four instars of larval development before pupation.

The eggs are orange, which is warning coloration that should deter egg-sucking predators.  But they are often attacked by syprhid (hoverfly) larvae, who apparently tolerate the milkweed poisons (cardiac glycosides) just fine.

Larvae may cannibalize each other at this stage, so that only a few survive to mature.  In fact, female milkweed leaf beetles may also cannibalize the offspring of other females, perhaps to reduce the competition for their own progeny on that plant.

I found only solitary individuals of milkweed leaf beetle larvae on the plants. This was one of the smallest — probably a second instar larva. Compare its size with that of the unopened flower to gauge how small it is.

A doubling of size occurs at each larval instar stage. This individual might be a third larval instar, with its much more ovoid abdoment, and more prominent head and thorax segments (compared to the individual in the previous photo).

This individual was almost as big as an adult and is probably a fourth instar, almost ready to drop to the ground and pupate in the soil or litter near the roots of the milkweed plant.

A fourth instar milkweed beetle larva is still mobile enough to turn the corner at the tip of a very pointed milkweed leaf.

There are reports on the web of milkweed leaf beetle infestations that completely denude their milkweed hosts of leaves and flowers, although this seems to occur primarily in a climate where milkweeds grow year-round.  The population of these beetles has definitely increased from a rare sighting of one individual several years ago, to finding many individuals in the backyard almost any day.  I hope this doesn’t mean I’ll have to manually remove beetles at some point — I already get enough practice doing that with Japanese Beetles.

Getting into focus

Last year’s big Christmas present was a new macro lens, which I didn’t get around to using until spring, because frankly it was too cold to try macrophotography outdoors last winter.  Apparently, I didn’t use it very much even then, because it was much easier to select the top ten “small things” photos than it was for the birds. But here they are — the top 10 macro shots of 2014, chosen for their color, variety, and potential biological interest.

An Orange Bluet male on a smooth, contrasting background of green.  I never saw one like this again, after I took this photo.

The contrast of black in the Black Swallowtail on the white of the Dutchman’s Breeches was the basis for this choice.  Finding nectar in early spring can be a challenge for early emerging butterflies.

In contrast to the shot above, the Tiger Swallowtail in a sea of summer wildflowers had numerous choices from a variety in the wildflower garden.

It’s difficult to choose such a noxious pest insect like the Squash Borer Moth for this collection, but it is a colorful insect caught in mid-flight (in focus!)

Another moth, rarely seen at rest — the Hummingbird Clearwing Moth (Hemaris thysbe).

One of several species of meadowhawks difficult to tell apart in their juvenile stages. They were very abundant in the wildflower garden this summer, hopefully gobbling up the many mosquitoes there.

I never realized what a popular flower Spiderwort is to insects. The Green Sweatbees, hoverflies, and bumblebees stocked up on its pollen in early spring.

Another rare visitor to the back yard (well, really a neighbor’s front yard) was this Leadplant Flower Moth, a specialist on said plant.  Read more about it here.

If you have ever been bitten by a 2-inch horsefly, here’s why it hurt. Those are a couple of shearing scissors up front in its mouthparts.

And lastly, the colorful Milkweed leaf beetles attempting to mate on a milkweed leaf. It’s more of a humorous shot really, since this male tried every which way to get into position.

Not hiding in plain sight

Brightly colored animals seem to flaunt the potential danger of being someone else’s dinner.  Calling attention to themselves with bright colors and flashy appendages seems counter-intuitive to survival.  So why do it?

It’s all about the advertising.  Bright color can be a warning to other animals.  Don’t eat me:  I’ll make you sick, my bite is lethal, I have a wicked sting.  You’ve undoubtedly seen these types of warnings in your garden.

Monarch butterfly orange and black warning coloration stands out on any background, but especially well on the purple blazing star. Photo by Karen Eckman

Some animals copy these bold aposomatic patterns, hoping to mimic the warning signal closely enough to avoid predation themselves.  Many insects copy the yellow and black warning coloration of bumblebees, hoping to fool a potential predator.

The things that sting have bright yellow and black coloration; some have fuzzy hair and some don’t — even that pattern is copied.

The mimics might even try to act like their models — hovering in front of flowers (hoverflies) or between perch sites (robberfly)

Some brightly colored fish purposely flaunt their colors to signal that they have a service to offer to others.

A brightly colored bluestreak cleaner wrasse hovers near the much larger and cryptically colored puffer fish to pick off parasites and extraneous food bits as a cleaning service.  Bright colors advertise the service at this “cleaning station”.  Photo from Wikipedia.

Bright colors in birds, especially the brightly colored plumes or other adornments projecting from their bodies, are a different kind of advertising.  By calling attention to themselves, colorful male birds are advertising their potential as a parent, or even just a sperm donor.  It’s as if they are saying to females, “I can survive in spite of attracting the attention of predators, or in spite of all these silly plumes that compromise by ability to escape, so choose me”.

A male peacock’s size may deter some predators, but all a predator has to do is grab hold of that long tail, and the advertisement becomes a liability.  Typically, the peahen raises the chicks, so all this male is advertising is his vigor (and sperm) as a potential mate.

Male Cardinals advertise more than just their vigor and ability to escape predation.

Bright colors mean the bird is in good health, and are an indication that these birds know where to find the food that makes them healthy, as well as brightly colored.  A female cardinal might choose one male over another for his ability to feed their chicks the right kind of food which, in turn, enhances their survival.  The female’s choosiness thus drives the male color pattern and feather adornments — sometimes to ridiculous or risky levels.  But if a flashy male survives the risks, then he’s the one.

Kit Day’s birds of Gambia:  

Specialists

Isn’t it strange that a plant that contains so many nasty chemicals (e.g., cardiac glycosides), as well as rubbery latex so alkaline that it can permanently scar the cornea of one’s eye, has so many insects that specialize on it?

But here they are — the amazing milkweed fauna:  lepidopterans, bugs, and beetles, consuming every part of the milkweed plant from its roots to its seeds — all seen in the backyard this summer.

The familiar Monarch butterfly caterpillar, munches away happily undeterred by the milky latex exuding from the leaves and stems of the plant.

The less familiar Milkweed Tussock Moth larvae — there were so many caterpillars on this particular milkweed plant, they completely defoliated it.

The tussock moth larvae grows some very long tufts and is not quite so gregarious when it’s older.

Milkweed bugs (true bugs — Hemiptera) are usually found on milkweed plants that have formed seed pods. They lay a clutch of bright yellow eggs on one of the pods, and the nymphs develop through five molts into adults by feeding through the pod wall on the seed endosperm.

Yellow aphids collect on milkweed stems and pods, but feed on the sugars passing through the plant’s phloem vessels, not the seeds. Small wasps (left center) parasitize the aphids by laying their eggs on the host.  Aphids are actually true bugs (Hemiptera), although these non-winged individuals don’t appear very bug-like.

The Red Milkweed Beetle is a member of the long-horned beetle family. They lay their eggs near the ground, and the larvae burrow into the roots and develop and overwinter there to emerge as adults the following spring.  Like the monarch butterfly larvae, milkweed beetles incorporate the milkweed’s poisonous chemicals into their own bodies, becoming distasteful to their predators.

Milkweed leaf beetles are members of the very large leaf-beetle family. They eat the leafy greenery, but the larvae are also known for consuming each other — their cannibalistic tendencies reduce competition for food in their local area!

Isn’t it ironic that in producing poisons to ward off herbivores, the plant becomes more attractive to specialist herbivores also trying to avoid predation?

A beautiful villain

I found one of the culprits that can cause cucumber wilt on some milkweed plants in a backyard nearby yesterday — the very attractive orange and black Squash vine borer moth (Melittia cucurbitae).  It’s too bad they are such damaging pests in the garden because they are quite photogenic.

It looks like a wasp from a distance with its striped body and long dangling legs, but is actually a member of the clearwing moth family (Sesiidae).

Long, highly “feathered” back legs drag behind the body as the moth flies, making it look like the wasp that it is trying to imitate.  But the clear, moth-shaped wings give it away, although these are not really visible to the human eye because they are moving so fast, they almost disappear.

The wings are just a gray blur in this photo, and you can clearly see the long proboscis inserted into the nectary of the milkweed flower — a very un-wasp like head. It looks like those hind legs also have some sharp spikes on them, as well as their feathery covering of scales.

Many of the species in the Sesiidae family are active in the daytime and are brightly colored, yellow and black or orange and black, mimicking bee or hornet coloration. This Batesian mimicry (in which a palatable species mimics an unpalatable or predatory one) presumably reduces their chances of being eaten by predators while foraging on flowers in the daylight.

At rest, the mimicry is closer to the real model, since its folded wings do resemble the shape of a wasp’s.  (This is probably the culprit whose larvae wilted my cucumber vines last year — feeding on the swamp milkweed flowers in my backyard.  You can read more about that here.)

Other members of the Sesiidae family are also agricultural pests, infesting fruit tree, vegetable, and timber crops, as their larvae bore into the woody stems or trunk and decimate the interior vasculature system of the plant.

The Clearwing Hummingbird Moth (Hemaris thysbe) is no relation to the garden villain above.  It’s a member of the Sphingidae family of hawkmoths, and although the larvae do feed on honeysuckle vines and some fruit trees, they don’t do nearly the damage that the Sesiidae species do.

This photo is from a recent post on critters of the northern bogs and forests, but the Clearwing Hummingbird Moth can be found almost everywhere in North America from Alaska to Florida.   Hawkmoths have a stouter, less slender body, shorter legs, and no scales on their legs, compared to the Squash vine borer moths. 

I’m not sure what the significance of clear wings is in these very different clearwing moth species.  Perhaps lack of scales on the wings means less air resistance during hovering flight, which both types of moths use for nectar foraging; or perhaps clear wings enhance their mimicry; or perhaps clear wings just present a smaller target to potential predators, since they appear almost transparent while the moth is flying.  Whatever the reason, the convergence of species from two different moth families is an interesting one.

In search of pollinators

The plight of the honeybees got top billing in the Minneapolis paper today, with a feature article on our endangered food supply that is so dependent on bee pollinators, honeybees in particular.

Bees of all sorts love the nectar of the late summer blooming sedums. I rarely see such a concentration of honeybees on a plant these days.

You might have known about the California almond crop dependency on honeybee pollinators (in fact, almonds are 100% bee pollinated), but broccoli, various fruits including cherries and blueberries, cucumbers, and melons (among 100+ foods we eat regularly) are also heavily dependent on bees for pollination and fruit set.  Honeybees are in trouble for a variety of reasons, many of which have to do with the impact of agro-chemicals on insects of all sorts.

Butterflies are less important for pollination of agricultural crops, but vital to the pollination of certain wildflower species. Butterfly weed (Asclepias tuberosa) probably got its name originally as a result of its attractiveness to a variety of butterflies (as well as bees).  But where are all the butterflies these days?

Their bright orange advertisement should bring pollinators running (or flying) to it, but ants were the only insects on this plant sitting in the middle of a 10 acre prairie.

Ruby-throated Hummingbirds enjoy the nectar that butterfly weed flowers have to offer, but they don’t move pollen from plant to plant. I never saw butterflies, and rarely any bees, on this plant in my garden, but they did manage to make a few seed pods.

Our local butterfly populations seem sparse compared to what they were a few years ago, whether a result of harsh winters, late springs, drought in areas through which they migrate, habitat destruction in their overwintering areas, or too many chemicals in the environment.

In a 3 hour walk around Tamarack nature center this morning, I saw this one Swallowtail butterfly (nectaring on Hoary Alyssum), one Red Admiral, and one Wood Satyr. Three butterflies in three hours — not a very impressive count.

In China, they pollinate fruit crops by hand — I hope that isn’t what we will have to resort to in the future.

A rare find

Despite having a lot of their favorite host plant (swamp milkweed) in my backyard, I have only seen the milkweed leaf beetle (Labidomera clivicollis) a few times.

Milkweed leaf beetles are vegetarian — they prefer the leaves and flowers of just about any milkweed species.  Their bold black and orange coloration warns predators to stay away from a potentially poisonous meal, but these beetles don’t sequester the toxic milkweed chemicals like  the monarch caterpillars do.

This is the only species of milkweed leaf beetle found north of Mexico, and is apparently pretty rare throughout some of its range.  Surprising, since its close relative, the Colorado Potato Beetle is a real pest.  But one researcher found that the larvae of this beetle are highly vulnerable to predation when they occur on milkweed species growing in an old field or prairie where the vegetation is continuous.  They survive much better on swamp milkweed where the plants might be surrounded by a moat of water, a barrier to the roaming predators.  Well then, welcome to my garden.

The one beetle I found in the morning acquired a friend by the evening. I imagine it’s difficult to stay affixed to a large, spherically shaped, slick, waxy object when your legs are too short to get a good hold. The male continually tapped the female’s back with his antennae while trying to jockey himself into position.

“Slip-slidin’ away…You know the nearer your destination, the more you slip sliding away.”  Paul Simon’s lyrics seem appropriate for this couple.

Nectar feast

Here it is almost mid-August already, and the insects seem to have just discovered all the milkweed in the backyard.  The hummingbirds prefer the orange-colored Butterfly Weed, but the butterflies, bees, wasps, and hover flies (syrphids) are buzzing the swamp milkweed.

Each flower head seems to be covered with three or four Great Black Wasps, some of which are enormous. 

Great Black Wasps are so large and fly so erratically around the backyard, it makes you want to keep your distance.  This wasp is one of the cicada killers that capture and paralyze their prey before laying a single egg on it in an underground nest.  You can read more about them in an earlier post.

One of the larger ones — almost 2 inches long.

Each milkweed flower has 5 hoods into which an insect could dip its tongue for nectar.  The Great Black Wasp foraging technique seemed completely random as they probed flowers in a very non-systematic way.  However, their foraging efforts were complicated by individuals continually buzzing each other. causing them to move to another flower head before they had finished probing all the flowers.

With their extremely long legs spread out over the entire flower head, Great Black Wasps come into contact with a number of the pollen sacs (pollinia) on the milkweed flowers, managing to remove them to carry to other flowers.  The left middle leg of the wasp in the photo below has three sets of pollinia attached.

A Yellow Jacket was furiously beating its wings trying to get its leg out of the slot in the milkweed flower where the pollinia are supposed to be inserted.  You can read more about how milkweed flowers are pollinated in an earlier post (click here).

In contrast, this little Aphrodite Fritillary sat on one flower head for several minutes turning slowly almost full circle, as it systematically sampled each hood of each flower.  When wasps or bumblebees approached that set of flowers, the butterfly simply flicked its wings a couple of times, and the encroaching insect moved off.

This Aphrodite Fritillary looks like it might have been grabbed by birds or dragonflies more than once.

It looks like the butterfly has one foot as well as its proboscis in the hood of the milkweed flower. Butterflies have taste receptors on their feet, so maybe it is sampling the nectar quality?

Milkweed plants provide a lot of nectar for a wide variety of insects, making the garden much more attractive to all sorts of wildlife.  The flowers are brightly colored, and some have a pleasant odor. Their one drawback is their tendency to plant themselves everywhere!

Timing is everything…

Last year we had an early spring (and not much of a winter), so the butterflies arrived and the bees appeared well before there were flowers to pollinate, or even leaves present as food sources for larvae.  Things were out of sync — badly, and I’m sure the insect populations took a nose dive in Minnesota as a result.

Last year, Monarch Butterflies were faced with laying their eggs on 6-8 inch tall plants. This photo was posted on May 12, 2012.

This monarch caterpillar tried to complete its development on this tiny milkweed, which was growing too slowly to keep up with demand. Ultimately, the caterpillar failed to metamorphose to a pupa.  This photo was taken June 26, 2012, and posted here.

This year, spring was 4-6 weeks late here, and also late perhaps further south of us as well.  We are well into summer, the flowers blooms are peaking in home and natural gardens, but pollinators are rarely found.  My raspberries have bloomed and set fruit, and yet I never saw a bee on the flowers the entire time.  Bumblebees are mostly absent, wasps are a rarity, honeybees and other small bees almost entirely absent.  We do have a lot of bee-mimic hoverflies (Syrphidae) though.

So, I was delighted to find a female Monarch butterfly in the backyard (first one this year!), depositing her eggs on a swamp milkweed plant.  The flower heads were still a couple of days from opening, but she was not trying to insert her proboscis into them anyway (proboscis is tightly coiled in the photo).

She probed the flowers and leaves repeatedly with her antennae (to determine whether it was in fact a milkweed plant?).  The proboscis is coiled up under her head.

Several times I saw her purposely lower her abdomen below wing level underneath a leaf, so I assumed she was laying an egg there.  When I checked those leaves,  sure enough, there were some little cylindrical eggs sticking up from the under surface (one per leaf).  I would have taken a photo, but they were much too small for my telephoto lens.

You can see the curvature of her abdomen better in this photo, and even imagine that there is a little white something being extruded from the tip onto the undersurface of the flower umbel (this is pure conjecture — I don’t know that they would lay an egg in a flower cluster).  Click on the photo for higher resolution of the abdomen.

I haven’t seen many photos of butterflies posted on the various blogs I read, so I wonder if this drought of butterflies is widespread over the U.S. (or other parts of the world) this year.  There are strange climatic swings everywhere that may well influence the insect populations (drastically), and that, in turn, would be devastating for our food production.