Friday, October 30, 2015

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

Monday, September 7, 2015

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).

Monday, August 3, 2015

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:

Wednesday, July 29, 2015

This place is hopping, part two

The water covering the ground gradually drained and evaporated away, slowly enough that the swarms of tadpoles had a chance to make the transition to a more terrestrial lifestyle.  Many of them still had a lot of growing left to do, though.

A toadling in the leaf litter.
As I walked through the forest, I kept sending waves of tiny toads hopping for cover.

A closer view of the toadling.
They were so small and well camouflaged in the leaf litter that they would easily have been overlooked if they had just remained still.

Another toadling blending in with the leaf litter.
However, the toadlings on the path through the woods faced a different problem.  They could not hop quite enough.  The raised edge of the trail proved too high an obstacle for their small legs, trapping them until they found some place to squeeze through.

A toadling thwarted by the edging of the trail.

Friday, June 26, 2015

This place is hopping, part one

Here in Houston we've been having a bit of rain recently (to put it mildly).  As a result, the woodland near my apartment became more of a wetland.  Not only did puddles appear all around, but so did plenty of frogs and toads ready to take advantage of them.  There isn't much action in the video below, but you can hear the calls of several eastern narrow-mouthed toads (Gastrophryne carolinensis) competing to attract mates.

Many frogs and toads had apparently already been successful in attracting mates, as the puddles were swarming with tadpoles of various shapes and sizes.

The trail through the woodland -- turned into a tadpole spawning ground.
The puddles were also excellent breeding grounds for mosquitoes, so I hoped that the tadpoles were feasting on all the mosquito larvae.

One of the larger tadpoles.
Meanwhile, some other animals proved to be better at coping with the new landscape than might have been expected.

A spider walks across one of the plethoric puddles.

Monday, June 22, 2015

More than an itch, part five

Near the leaf-footed bug nymphs on the lantana were a couple of my favorite bug nymphs.  As adults, they look like typical bugs, but as nymphs they look remarkably like ants!

A broad-headed bug (Alydidae) nymph.
Nevertheless, they can be distinguished easily from real ants (such as the one pictured below) if you know where to look.  Despite mimicking an ant's appearance in many ways, these nymphs still have the long mouthparts characteristic of bugs.

A carpenter ant (Camponotus sp.).
The ant mimics also don't act much like ants.  When they are approached, they quickly run for cover and unlike some other bug nymphs, they aren't quick to return.

The ant mimic scurries away.

Friday, June 19, 2015

More than an itch, part four

Like the bordered plant bug nymphs, leaf-footed bug nymphs are often found gathered in groups.  Therefore, the bug nymph pictured below appears to be unusually alone.

A leaf-footed bug nymph (Coreidae) on a lantana leaf.
However, looking from another angle reveals that the "lone" bug nymph is actually just the tip of the iceberg of bug nymphs!

Many more leaf-footed bug nymphs hanging underneath the leaf.
The large group of bug nymphs shared the limited space on the underside of the leaf peacefully.  However, another group feeding on unripe lantana berries nearby was not nearly so tranquil.

As I watched, an extended fight broke out between two of the nymphs.  They may have been competing over access to the berries.  Yet, there seemed to be plenty of berries available, which should have made a fight unnecessary.  An alternative explanation is that one of the nymphs may have tried to switch from eating berries to eating the other nymph, as some bug species are known to be cannibalistic.

Wednesday, June 17, 2015

More than an itch, part three

For most insects, tiny bug nymphs pose a negligible threat.  The threat is hardly increased when the nymphs are in a group (which they often are).  However, unlike the beetle being assailed by the stink bug, there are some potential victims that lack the mobility to attempt an escape.

A group of bright red bug nymphs (Largus sp.) feeding on a white object.
The group of bug nymphs pictured here had located one such immobile victim on a leaf.  In order to see what they had found, I blew air at them.  The nymphs quickly scattered across the leaf, revealing a while cocoon.

The bugs scatter revealing a cocoon.
Nearly as quickly, the bug nymphs began to return to the cocoon and to resume feeding on whatever had been developing inside.

The bugs begin to return.

Monday, June 1, 2015

More than an itch, part two

Compared to the assassin bugs, stink bugs (Pentatomidae) may seem to be unlikely predators. While most stink bugs do stick to feeding on plants, some supplement their diets with insects. Others are pure predators.

A leaf beetle (Ophraella sexvittata) being attacked by a predatory stink bug (Perillus sp.) on a goldenrod (Solidago sp.) leaf.
A few of the predatory stink bugs are even used to control agricultural pests. However, the stink bug shown here had trouble controlling just one small beetle.

The beetle struggles to get away.
The stink bug appeared to have pierced the beetle with its mouthparts, yet the beetle showed no sign of giving up.

The bug continues to pull away.
I did not see whether the beetle escaped in the end. Yet, what I saw when I came back several days later convinced me that neither the stink bug nor any other predators had been very successful in reducing the beetle population.

The goldenrod plants later that week.

Wednesday, May 6, 2015

More than an itch, part one

For an insect, a bug bite is likely to be a life threatening affliction.  Although most of the creatures we think of as delivering "bug bites" are not true bugs (i.e., they do not belong to the order Hemiptera), there are several groups of predatory true bugs.  Given their name, it should come as no surprise that the assassin bugs are a prime example.

An adult milkweed assassin bug (Zelus longipes).
I frequently find assassin bugs on plant foliage, waiting in ambush.  More rarely, I see one that has had recent success in capturing a smaller insect to consume through its sharp, straw-like mouthparts.

A milkweed assassin bug nymph with its prey.
Flowers are also good locations to ambush insects, so when I started spotting milkweed assassin bugs on flowers, I initially assumed that they were waiting to catch unwary flower visitors.  However, the orange and black bugs were so conspicuous against the white petals that any insect landing on those flowers would have to be extremely unwary.  Then, I noticed that some of the flowers hosted not just one, but two assassin bugs -- making the chances of a successful ambush even slimmer.  Only once I was able to inspect the photographs did it become apparent that the assassin bugs had a different motivation for coming to the flowers.

The milkweed assassin bugs also seem to feed on flowers.
Instead of hunting insects attracted to the flowers' nectar, the assassin bugs appeared to be drinking the nectar themselves!

Monday, April 27, 2015

Paying for the click

This weekend, I was trying to evade the mosquitoes swarming around me when I saw a much larger insect flying slowly down the trail.  It soon landed on a vine a short distance away and I recognized it as a click beetle.

A Texas click beetle (Alaus lusciosus).
Although this click beetle did not have the glowing spots that had first made me fascinated with click beetles, its prominent eye-spots, large size, and loud clicks still made it very impressive.

The big spots on top of the beetle are not its real eyes.
For a demonstration of the clicking behavior, watch the video below.  If you happen to find a click beetle yourself, I do not recommend that you attempt to provoke it into clicking.  As I discovered somewhat painfully, when clicking fails to deter the harasser, the beetle may resort to biting.

If you watch the slow-motion part of the video carefully, you can see that the 'jump' is not caused by the beetle snapping back against my hand (as I had initially thought).  Instead, the beetle lifts its head away from my hand and then the rest of its body just pops into the air.  The key to the click and jump is the spine that extends down from the underside of the head.

The underside of the Texas click beetle.  Note the spine used in clicking and the sharp mandibles used in biting.
The beetle produces the click by first catching the end of the spine into a notch, which prevents the beetle from moving as it contracts a large muscle that connects its body segments.  Then, when the spine slides out of the notch, the energy in the muscle is rapidly released, propelling the beetle into the air.

Explore some more: The Click of the Click Beetle (a full explanation of the physics of the click)

Monday, April 13, 2015

Going to ground, part two

Goatweed leafwing butterflies may not be as bright and conspicuous as many other butterflies are, but they do not look much like leaves either.

A goatweed leafwing (Anaea andria) perched on a branch.
At least, they are not very convincing as leaves when they are sitting in trees (which they often are).

A goatweed leafwing butterfly hanging upside-down from a branch.
It is a completely different matter, however, when the goatweed leafwing sits underneath a tree in the leaf litter.  There, it becomes very difficult to distinguish from the surrounding leaves.  To see how well-camouflaged the goatweed leafwing can be, try finding it in the three pictures below!

Can you find the goatweed leafwing?
I promise, there really is a butterfly in each of these pictures.

The butterfly moved.  It might be slightly easier to find this time.
When I was taking the pictures, I had the advantage of seeing the butterfly land and then walk around.

The butterfly moved again.  It should be easiest (but maybe still not easy) to see in this picture.
To see the butterfly locations revealed, go here.  I've edited the photos to make the butterfly pop out from the background.

Monday, April 6, 2015

Going to ground, part one

The butterflies visiting the lantanas were quite conspicuous as they moved from flower to flower drinking nectar.  Nevertheless, if threatened, they could quickly vanish from sight.  As I described before, the cloudless sulfurs often disappeared by flying off into the woods.  However, sometimes they just landed on the grass -- and were gone.  Despite the fact that cloudless sulfurs are yellow, I would completely lose track of them in the grass if I took my eyes off them for a moment (which always seemed to happen when I tried to approach slowly and without stepping in a fire ant nest).

I frequently step in fire ant nests.  Fortunately, if I am wearing my rain boots, I tend to notice the ants in time.  Unfortunately, I am not always wearing my rain boots.
The boldly-colored red admirals could also camouflage themselves on the ground...

A red admiral (Vanessa atalanta) sunning on the ground. closing their wings together and showing only the mottled, brown undersides.

The red admiral with its wings closed.
For the next post, be prepared to put your hidden-butterfly-finding skills to the test!

Wednesday, April 1, 2015

A tough egg to crack

Last summer, I kept seeing song sparrows and gray catbirds coming in and out of a dense patch of rosebushes.

A song sparrow (Melospiza melodia) emerging from the rose bushes.
I guessed that they had built nests somewhere deep inside.  Although I eventually found the song sparrow nest, I was disappointed that I could not locate the catbird nest.  So, as a surprise, my mother put a wooden egg in an old nest and left it for me to stumble upon.

A large, blue egg in a nest.  (Not a real egg.)
 However, something else found the egg first.

When I heard crows squabbling, I looked out and saw that one of the crows was sitting on the ground by the rosebushes and attempting to eat what appeared to be a gray catbird egg.  Of course, not knowing that a wooden egg had been placed outside just minutes before, I assumed that the crow had found and raided the catbird nest.  The truth only emerged when I shared the sad news about the catbird nest with my mother.  She quickly led me to the nest where the wooden egg had been. As she had suspected, the nest was empty.  When the wooden egg finally reappeared in the yard several days later, it was in splinters.  (The photograph of the egg in the nest above showed a reenactment using a spare egg.  We immediately brought that second egg back inside!)

Friday, March 27, 2015

Springing to life, part two

Instead of visiting the bluebonnets, many of the butterflies that I saw this weekend were gathered around several large lantana bushes.

A fiery skipper (Hylephila phyleus) on lantana flowers.
Some of the butterflies, such as the fiery skipper above and the red admiral below, remained focused on the flowers despite the approaching camera (and camera wielder).

A red admiral (Vanessa atalanta).
However, a couple of other species were consistently more challenging to approach.  Common buckeyes have the tantalizing tendency to fly just a few feet away each time I get almost close enough for a good shot (which has led to several very low-speed chases).

A common buckeye (Junonia coenia).
Meanwhile, with cloudless sulfur butterflies, I would have only one chance to approach as non-threateningly as I could.  If disturbed, these butterflies would nearly always disappear off into the woods...

A cloudless sulfur (Phoebis sennae).
...and they were very easily disturbed!

The cloudless sulfur dropping backwards off the flowers in order to fly away.

Wednesday, March 25, 2015

Springing to life, part one

Just in time for the first days of spring, the Texas bluebonnets spread from sparse glimpses of blue to cover all the nearby meadows.

A field of Texas bluebonnets (Lupinus texensis) in bloom.
Though the bluebonnets were not yet swarmed with visitors (the way they were last spring at the peak of their bloom), I found a variety of insects on the blossoms, including honey bees, lady beetles...

A seven-spotted lady beetle (Coccinella septempunctata) on a bluebonnet inflorescence. 
...and even large, menacing wasps.

A paper wasp (Polistes sp.) feeding from bluebonnet flowers.
However, the many butterflies that also appeared with the mild spring weather were mostly attracted to another type of flower.  To be continued...

Friday, March 13, 2015

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