A caterpillar green around the gills, part two

After emerging from their caterpillar host, the young wasps quickly lost their plump, bright green forms.

Day 1: The wasp larvae (right) emerge from the moth caterpillar (left).

Over the next two days, they first faded to a dull yellow...

Day 2: The wasp larvae begin to pupate.

...and then shriveled and blackened.

Day 3: The wasp larvae have become pupae.

However, the wasps were not sickening and dying -- they were progressing normally through their development from larvae to pupae. Meanwhile, the moth caterpillar that stood by, apparently healthy except for its inertia, had its own development frozen. To be continued...

A caterpillar green around the gills, part one

This Halloween, instead of featuring a seasonable insect or spider, I will share a spooky story of a "possessed" caterpillar.

Parasitoids may be among the smaller enemies that a caterpillar has, but they are also among the most insidious.  When a female parasitoid (generally a small wasp or fly) finds a suitable caterpillar, it lays its eggs on or even inside the caterpillar.  The parasitoid larvae then emerge from the eggs and proceed to feed on the caterpillar.  What becomes of the caterpillar once the parasitoid invasion is complete?  It may be mummified, vanish from inside a fuzzy shroud, or perhaps more strangely -- be left apparently unharmed.

A copper underwing (Amphipyra pyramidoides) caterpillar and recently emerged parasitoid wasp larvae.

The light green caterpillar shown above and below is surrounded by the darker green larvae of a parasitoid wasp.  The wasp larvae had recently finished feeding inside the caterpillar and had broken through the sides of the caterpillar to finish their development outside.

The slits that the wasp larvae emerged through are visible behind them.

Meanwhile, the caterpillar just sat there as if unperturbed by the litter of parasitoids.

However, the caterpillar was hardly passive.  When the parasitoid larvae were threatened by an approaching object, the caterpillar became surprisingly aggressive.

The parasitoids had left the caterpillar alive, but not at liberty.  Though the caterpillar was no longer needed as food, it could still be manipulated into serving as the parasitoids' protector.

To be continued... but in the meantime, you can explore some more: Parasitoid Increases Survival of Its Pupae by Inducing Hosts to Fight Predators

Synchronized twitching

The fall webworms' silk nest forms a formidable defense; however, the caterpillars do not always rely on the protective layer alone.

A dense group of fall webworms (Hyphantria cunea) inside a silk nest.

In order to construct and extend the sheets of silk, some of the caterpillars spend time exposed on the outside of the nest. There, they take advantage of their numbers to defend themselves in another way -- by making a coordinated, threatening display. 

The synchronized action of the caterpillars is thought to discourage predators and parasites.  Though the twitching sometimes appears to begin spontaneously, it can also be triggered when something approaches the caterpillars.  For example, in the video above, the last bout of twitching appears to be in response to the arrival of a small fly or wasp on the other side of the nest (~1:44).

On the safe side

When feeding in a large group, caterpillars may be more noticeable to predators -- but they may also be better able to defend themselves.  Groups of tent caterpillars and webworms can consist of hundreds of individuals, which makes them easily spotted (and probably smelled) even from a distance. To thwart their many enemies, these caterpillars surround themselves and their feeding zones with a protective netting of silk.

A nest of fall webworms (Hyphantria cunea) on a mulberry branch.

The caterpillars then proceed to devour nearly everything within their tightly woven nest.  As they move along a branch, all that they leave behind are leaf skeletons wrapped in silk.

The larvae can completely skeletonize large leaves.

Meanwhile, any predators that locate the caterpillars are likely to depart without obtaining a meal. Watch a wasp get foiled by the silk enclosure in the video below:

The caterpillars eat their match, part three

Compared to the orange-barred sulphur butterflies, adult geometrid moths do not appear very active (at least not during the day)...

A pale beauty moth (Campaea perlata).

...and most of them are not very bright or flashy.

A large lace-border moth (Scopula limboundata).

However, geometrid caterpillars can be just as impressive as orange-barred sulfur caterpillars when it comes to blending in with the flowers that they eat.

A purple geometrid caterpillar on purple flowers.

In addition, at least some geometrid caterpillars have the same ability to change their color in order to match their background.  

A pink geometrid caterpillar on a pink rose blossom.

Although many geometrid species feed on other parts of plants (and mimic those instead), there are well over a thousand species of geometrid moths in North America -- including plenty of ones with colorful, flower-eating caterpillars.  See a few more of them here: Geometrid larvae on flowers

The host with the most, part two

The mining flies and galling mites inflicted peculiar injuries to the lantanas, but last year I saw plenty of ordinary herbivory of lantanas too.  Of course, after finding evidence of herbivory, I sought out the herbivores themselves.

A lantana leaf fastened in half by silk.

When the damage was fresh, I did not have to look far before finding the herbivore.  One type of caterpillar, the lantana leaftier moth, made pouches out of the lantana leaves by tying them with silk.  It then consumed the leaf down to a membrane while remaining concealed within the folded leaf (until I came along and pulled the leaf open).

A lantana leaftier moth (Salbia haemorrhoidalis) caterpillar eating the leaf from within.

Another, much larger caterpillar made an even more complete meal of the lantana leaves.  After it had finished with a leaf, there was often not much left besides the tough central vein.

A lantana after a visit from a very hungry caterpillar.

Looking for the first relatively intact leaf adjacent to the consumed leaves, it was easy to find the lantana moth caterpillars that were responsible for the devastation.

A lantana moth (Diastema tigris) caterpillar underneath a lantana leaf.

Bad hair

Out for a walk after a storm, I did not find that any more dangerous trees had fallen.  I did, however, come across a fallen tree of the regular variety and something dangerous that seemed to have fallen out of a tree.

A late instar puss caterpillar (Megalopyge opercularis), known as a flannel moth as an adult.

It was a caterpillar covered in such a dense coat of hair that it initially looked like a moving scrap of fur.

* To see this video in high definition (1080p), you may need to: 

(1) click "YouTube" to watch on the YouTube website

(2) change the settings at the bottom of the video screen

While these caterpillars look soft and furry, leading to the name "puss caterpillars", their appearance is deceptive.

The head and part of the body sometimes emerge from under the hair.

The hairs conceal numerous venomous spines capable of delivering an exceptionally painful sting.

The hair-line recedes.

Between encounters with fire ants and an upside-down jellyfish, I've had more than enough painful stings recently.  Fortunately, I was able to avoid any direct contact with the puss caterpillar.

It is more recognizable as a caterpillar from underneath.

Explore some more: Toxic "Toupee"

All sewn up, part three

After sealing itself up inside the hydrangea leaves, what did the hydrangea leaftier caterpillar do?  From the outside, there was no obvious sign that the caterpillar was feeding on the leaves.

Hydrangea leaves after an encounter with a hydrangea leaftier (Olethreutes ferriferana) caterpillar.

Pulling apart one of the older leaf capsules to see what was happening inside, I found something that did not look very much like a caterpillar.

Nested inside the sealed leaves was a sealed bundle.

It looked a lot like a clump of moldy frass, but I tried separating it anyway -- and out popped a twitching pupa.

Inside the cocoon was a hydrangea leaftier (Olethreutes ferriferana) pupa.

By tying the hydrangea leaves together and then forming a cocoon inside, the caterpillar had made a snug refuge with multiple layers of security to protect it during its metamorphosis into a moth.

All sewn up, part two

A few days after first observing the strange affliction of the hydrangea leaves, I managed to find a set of leaves that were only partially sealed.

Hydrangea leaves partially woven together.

Lines of silk laced back and forth between the leaf margins, leading up to the weaver itself: the aptly named hydrangea leaftier.

A hydrangea leaftier (Olethreutes ferriferana) moth larva.

Weaving the hydrangea leaves together is a big -- and very slow -- job for such a small caterpillar.  Here is a brief clip showing the weaving process up close and then zoomed out to show the extent of the task...

* To see this video in high definition (1080p), you may need to: 

(1) click "YouTube" to watch on the YouTube website

(2) change the settings at the bottom of the video screen

...and here is a longer clip, played at 32x actual speed, to illustrate how the leaves are pulled together by the caterpillar.

* To see this video in high definition (1080p), you may need to: 

(1) click "YouTube" to watch on the YouTube website

(2) change the settings at the bottom of the video screen

An agreeable face

To move on from a rather disagreeable tail, here is an agreeable face...

An agreeable face?

... or at least, the face of an agreeable tiger moth (Spilosoma congrua).  Certainly, there is something about this particular specimen that makes it seem distinctly less than agreeable.

The agreeable tiger moth in full.

From the point of view of gardeners, however, these moths should indeed be an agreeable sight.  Adult moths produce caterpillars -- and the caterpillars of this species eat a variety of troublesome weeds, including dandelions (Taraxacum spp.), knotweeds (Polygonum spp.), plantains (Plantago spp.), wild lettuces (Lactuca spp.), and white goosefoots (Chenopodium album).

Explore some more: HOSTS - a Database of the World's Lepidopteran Hostplants

Caterpillars on the grass, part four

By the time fungus-infected caterpillars crawl up to the tops of grass stems  (or to other elevated positions), they are almost certainly doomed.  Therefore, it might seem reasonable to assume that this 'height seeking' behavior is instigated by and for the benefit of the fungus.  Yet, there is another possibility.

Though it is too late for the dying caterpillars to save themselves, they may be acting to save their relatives.  Female moths and butterflies sometimes lay their eggs in clumps, with the consequence that sibling caterpillars develop in close proximity.  For these families, it would be advantageous if diseased individuals left the group to avoid infecting the others.  Furthermore, being stuck at the top of a grass stem may have significant drawbacks for the fungus if large herbivores or predators of the caterpillars are around.

Whether climbing up grasses was more beneficial for the caterpillars or the fungus, there were some caterpillars that avoided infection.  About the same time and in the same area that I found the sick, green caterpillar, I caught a much healthier version that had been crawling across the ground.

A healthy moth caterpillar.

I took the healthy caterpillar home to observe whether it too would fall victim to the (at the time) mysterious epidemic.  However, unlike the sick caterpillar, which was rapidly engulfed in fungus, the healthy caterpillar soon metamorphosed into a pupa...

A healthy moth pupa.

... and later emerged as a nondescript, grayish brown moth.

Another tuft customer

Although the small, tufted moth was unusual, it is not the strangest tufted moth that I have seen.  That dubious honor goes to the common looper moth (Autographa precationis) that I encountered last fall. 

A common looper moth (Autographa precationis).

From above, the common looper moth has an odd shape, but it doesn't seem all that impressive.  However, viewing the moth from the front reveals an elaborately curved tuft crowning the moth's head.

The common looper moth from the front.

The tufts don't stop there either.  The common looper moth has a row of three tufts down its back and the raised corners of its wings form what looks like a small, fourth tuft.

A profile view of the common looper moth.

Despite its name, this creature did not look much like a common moth to me -- and if it had been on some tree bark instead of the window, it might not have looked like a moth at all!

One tuft customer

Frequently, I will approach a leaf to investigate a mysterious object resting on its surface... only to discover a bit of debris that has fallen from some other plant.  However, every once in a while, my curiosity is rewarded.

Just some debris on a leaf?

The speck on the leaf shown above, although not very promising from a distance, turned out to be one of those rare objects that merited a closer inspection.

A small moth with a large tuft.

It was a small moth that had managed to obscure its shape by tucking in its legs and folding back its antennae.  Another unusual feature that stood out (quite literally) from the moth's otherwise streamlined appearance was a dark brown tuft of scales behind its head.  As I studied the moth from a variety of angles, it began to attract some more intimate attention.

An ant approaches the moth.

An ant came up and used its antennae to feel the moth.  For a moment, neither the ant nor the moth made a move and I wondered if the ant would attack.  Then the moment passed and the ant continued on its way, leaving the moth behind as if it really were just an uninteresting bit of debris.

The vanishing act, continued

After the caterpillars on the papaya had all disappeared into thin air (surrounded by white fuzz), the papaya leaves were left to grow undisturbed once again.  Yet, not that many days went by before I began to notice a new set of bites taken out of the leaves up at the very top of the papaya.

Papaya leaves with some tips chewed partially off and other tips completely gone.

Another sphinx moth must have visited the papaya to lay her eggs and make the tree play host to a new batch of caterpillars.  How many caterpillars were in this new batch?  Standing on the ground it was difficult to see up to the top of the tree and I only spotted one caterpillar.  However, with the help of my camera, I was able to count not just one, but seven new caterpillars.

The seven caterpillars circled in red.

That is, I counted seven new caterpillars just on the small part of the papaya shown in the pictures above.  I didn't count how many caterpillars were gobbling up the rest of the papaya leaves.  Happily, however many caterpillars there were, they didn't stop the tree from also producing a nice batch of papaya fruits.

Papaya fruits growing from the trunk of the papaya tree.

The vanishing act

The monarchs were not alone in facing danger in the garden this winter.  On the papaya, there were signs that Alope sphinx moth (Erinnyis alope) caterpillars had been chewing on the edges of the leaves.  However, the caterpillars themselves were nowhere to be seen.  These caterpillars can be well camouflaged against papaya leaf veins, but in this case the caterpillars were not simply disguised.  The caterpillars were gone, and in their place, something else was lined up along the leaf veins.

A ball of white fuzz along a papaya leaf vein.

On several of the papaya leaves, there were fuzzy white objects.  Although the objects were roughly cocoon shaped, they were obviously not the cocoons of the sphinx moths (which pupate on the ground).  Looking from another angle, I could tell that the white fuzz was hollow inside -- just as if it had been made around a caterpillar.

The hollow center of the white fuzz.

Indeed, it looked that way because it had been shaped around a caterpillar.  Parasitic wasp larvae had eaten the caterpillar and then spun their own cocoons within a fuzzy matrix around the quickly disappearing remains of their host.  In a previous year, we kept some of this white fuzz in a jar to find out what was inside; the result was a jar full of tiny black wasps!

Explore some more: Erinnyis alope life cycle

Purple insect eater

In most consumer-resource interactions between plants and insects, the plant is the one that gets consumed.  However, a few groups of plants have been able to reverse the relationship.  Insects and other small animals come to these plants for a meal, only to become one themselves.

A purple pitcher plant (Sarracenia purpurea) in bloom.

One of these carnivorous plants, the purple pitcher plant (Sarracenia purpurea), lures visitors onto its leaves with colorful markings and nectar secretions.

Dead insects, including a moth, in a pitcher plant leaf.

Once on a leaf, visitors become trapped due to the leaf's waxy surface, steep angle, and downwards pointing hairs -- and possibly due to being drugged (a narcotic compound has been found in the secretions of a related species, S. flava).  Even flying insects fall into and then drown in the pool of rainwater at the base of the leaf.

Flies and springtails trapped in another leaf.

This water also contains digestive enzymes secreted by the leaf and a community of bacteria, which together break down the victims of the trap.  The leaf can then absorb nutrients that the plant might not otherwise be able to obtain from the poor quality soil in its boggy habitat.

A carabid beetle attempting to escape the pitfall trap.

Know thy host

Picking the right spot to lay eggs is a challenge shared by many insects.  While most adult insects can fly, immature insects tend to be more limited in their movement.  Therefore, in addition to the safety of her offspring, the mother must ensure the availability of the right food -- and in adequate amounts.

A common aspen leaf miner (Phyllocnistis populiella) about to run out of leaf to eat.

Perhaps the mother of the leaf miner larva above should have chosen a bigger leaf.  Yet, young (and thus small) leaves may confer their own advantages, including being more tender and consequently easier to eat.  Indeed, young leaves are often preferred by a variety of herbivores.

On a side note, how does one identify an insect that is still inside a leaf?  The trick is to know the leaf.  Since leaf miners tend to be specialized on one or a small number of plant species, identifying the plant can lead to the identity of the leaf miner.  For example, identifying the leaf above as belonging to a quaking aspen (Populus tremuloides) quickly led to the identification of the larva inside.  Even when more than one leaf miner species uses a plant, the leaf miners will usually differ in the type of mine they create (see some other examples here and here).

The better to smell you with

As I walked through one of the small parks in my neighborhood, I noticed a small moth flying along the path.  Holding my breath, I hoped fervently that it would land somewhere nearby.  Why did I care so much about getting a better look at a little moth?  The answer is that I had never seen one like it -- and that it had seemingly impossibly long antennae.

A male fairy longhorn moth (Nemophora sp.).

Luckily for me, the moth did land right beside the path.  Approaching cautiously, I was surprised to see that it had stunning wings, with iridescent yellow, blue and purple markings and a fuzzy fringe.  I was still more impressed by the antennae, though, which were so long that they had made the moth's flight appear somewhat awkward.

Another view of the fairy longhorn moth (Nemophora sp.).

Moths use their antennae for smelling.  They can use their acute sense of smell to locate nectar to drink, host plants where they can lay their eggs, and mates.  Although both male and female fairy longhorn moths (Adelidae) have long antennae, those of the males are significantly longer and can be several times the length of their wings.  The males may use their long antennae to detect pheromones released by the females, or perhaps to locate other males, since male fairy longhorn moths are known to swarm in large groups.

Yet another view of this amazing little moth.

More than meets the eye

As I was on my way to the grocery store, I noticed that I shared the sidewalk with a much slower walker... one that was just inching along.

A geometrid caterpillar (Geometridae) inching its way across the sidewalk.

I crouched down to watch this geometrid caterpillar, more commonly known as an inchworm, as it crossed the sidewalk.  However, other pedestrians, who seemed intent on ignoring both me and whatever I was looking at, nearly stepped on the caterpillar.  Therefore, I decided to aid the caterpillar in its journey and gingerly picked it up.  Suddenly, something unexpected happened: the caterpillar went rigid and transformed into a twig.

The same caterpillar doing an impressive imitation of a twig.

Or, at least, the caterpillar took on the appearance and texture of a twig -- which might have been very helpful for the caterpillar had I been a bird looking for its next meal.