Parasitism in Caterpillars

While investigating leaf rollers and leaf miners as a part of our ongoing nature studies, we came upon a video on YouTube that perplexed me.  Ten years ago (eeek, has it really been that long?) I had the remarkable opportunity to take part in an Earthwatch expedition to Ecuador, Rainforest Caterpillars.  The focus of our assignment was on parasitism in caterpillars and while I am by no means an expert, I consider myself an insect enthusiast and can identify which insect order most specimens belong.

[ Edited :: This video has since been removed and I have been unable to find it – or a substitute.]

This video intrigued me because one of the things we did while in the field was ‘torment’ the caterpillars we found.  Essentially, we would do this by gently petting them with a small paint brush and pinching them carefully with a pair of tweezers (enough to get a reaction but not to harm).  We would then record their behavior or reaction to the stimuli.  We did this to get a general idea of how the different species would defend themselves and observed a wide variety of behaviors including thrashing about, rearing up and attempting to bite the attacker (that would be us), as well as and most amusing,kicking frass at us.

The premise, as you’ll see when you watch the video, is that the caterpillars behave this way because they have been parasitized by a wasp and their behavior is not altered or controlled by the wasp.  I didn’t think this was exactly the case.  I thereby contacted the lead scientist with whom I worked and inquired about the validity of the video.  His response confirmed my suspicion:

“This braconid genus, Glyptapanteles, is one that we rear a lot in Ecuador from geometrids.  The video that you saw, and the paper in PLOS one about this is not necessarily that common.  More generally, parasites do change the behavior of their hosts to the benefit of the parasites, but thrashing is still a very effective defense for most caterpillars against a broad array of predators and parasitoids.”  ~ Lee Dyer

For your educational entertainment, I include this video showing a Tobacco Hornworm, Manduca sexta, caterpillar infested with parasitoids.  The  Braconid wasp, Cotesia congregate, lays its eggs in the body of the caterpillar, also depositing a virus which is thought to prolong the larval stages and prevent molting to the pupal stage. When the wasp larvae are mature, they burrow out through the caterpillar’s skin and make white silken cocoons on the surface. In this video, two newly emerged wasp larvae are spinning their cocoons.

Leaf Rollers .. an Update

When weren’t successful hunting leaf rollers and miners when we had gone on our nature outings.  As luck would have it, when we weren’t looking for them … that is when we find them.

First … when I was on a run and the kids were at Enrichment Day … I observed one and immediately planned to bring  it back with me. I wasn’t sure how to ensure the little critter didn’t fall out of his roll while I ran but I opted to continue my run and collect the specimen on my return.  Fortunately, I observed a plastic bag the wind had blown up against a fence and I thereby picked it up.  I then carefully collected the leaf home and hopefully, its inhabitant on my return loop.

Sweetie’s journal entry shown in left photo, on top.  Buddy’s entry is on the bottom as well as the photo on the right.

When I shared my discovery with the kids later that afternoon, they were overjoyed.  They ran to their journals and immediately got started on sketching the leaf and whatever surprise might be inside.  They were amazed by the tiny little “stitches” as they referred to the silk thread the insect had used to ensure it’s efforts weren’t wasted.  We they unrolled the leaf, we found lots of frass (caterpillar poop) and to our joy, a tiny little caterpillar no longer than 1cm.  Sadly, he had perished.

A week later, we were on a nature outing with our new Roots & Shoots group and low and behold, leaf rollers were everywhere.  It was a delight that now we were able to share our knowledge with others.

 How many rolled leaves do you see?

 Buddy reveals the frass inide one of the rolled leaves .. evidence of it’s former inhabitant.

Unfortunately, of all the leaves we unrolled (just one a piece), none had critters within.  It was a remarkable day though … as you’ll discover in followup posts … we all made many wonderful discoveries. 

Leaf-Miners & Rollers :: Nature Study

When I discovered that one of the Outdoor Hour Challenges this month is Leaf-Miners and Rollers, I was delighted.  I love insects and enjoy sharing my knowledge with others, particularly my munchkins.  This time around … I was pleased when my daughter asked me a question that allowed me to introduce her to using a dichotomous key.  I’ll come back to that, but let me first set the stage.

After following Barb’s wonderful suggestions for Inside Prep Work, we went outside with the intention of looking for and observing insects.  Coincidentally, we walked about in two locations … first on the coast when we were visiting the grandparents and second, when we returned home to Northern California.  Unfortunately, I was not aware of any of the suggested plants in either area so we had to make do with a hunt of sorts.  At home, we do have many species of oaks but weren’t successful finding leaf-miners at work.

As suggested by Barb, we examined various leaves and looked for anything that had damaged the leaves. We found evidence on some blackberry leaves of what may have been leaf-miners, but we are not certain.  We also observed numerous leaves with leaf margins chewed away by insects.  In an apple tree, we observed a ripe apple but upon picking it, discovered nearly 1/3 of it had been pecked away by birds (it was too high for deer).

We are in the midst of a GEMS unit, Investigating Artifacts, so we also collected numerous natural objects.  We thereby picked a few leaves that had evidence of insects and brought our collections back to the house for further investigation.  We spent a little time sorting our collection into different categories as a part of the Artifacts unit (leaves/not leaves, seeds/not seeds, green/not green, etc.) and then proceeded with our OHC challenge on leaf-miners and leaf-rollers.

I explained that my expectation for our journal entry was to illustrate 2-3 specimens of their choice.  I should have asked them to write a few words about our quest as well and/or to write a few facts about what they chose to draw … note to self for next time.  I was very impressed with how careful each one was with their drawings, though.  They both took the time to do their best and for that I am thankful.

While we were journaling,  however, a little critter came out amongst the leaf litter to make our acquaintance.  He observed us for a long time and seemingly, enjoyed the attention because he posed for a long time while in turn observed him.  He even allowed us to sketch him and was kind enough not to wiggle about … the perfect model!  🙂

As we were sketching, Sweetie asked me what kind of bug he was.  I explained that he belonged to the order of insects called Hemiptera or true bugs.  This is when she posed her question, “How do you know, Mom?  How can you tell?”

I thereby retrieved the dichotomous key that I had used for years in the classroom.  It was the perfect companion lesson to the discussion we had had just moments before when we were sorting our collection into different categories.  I walked through the key with her, allowing her to discover for herself what characteristics our little insect friend had that classified him as Hemiptera.  She was so interested in the key that she then asked if she could make one of her own for her journal.  What a great idea!!

I am linking this up at Handbook of Nature Study.

School of Ants

In July, we signed up to participate in a new citizen science project called, School of Ants.  We received our collection kits late last week and were anxious to get started.  We received 4 complete collection kits.  Each kit contained 9 collection vials (4 red for sidewalks and 4 blue vials for green spaces, and 1 large orange vial for anything else we might collect). 

We took out and read the instructions.  The instructions stated that all 4 vials of one color (blue or red) from one kit should be placed in one area, approximately a foot apart.  When we were comfortable with what we were expected to do, we brainstormed where we wanted to place the collection the vials.  Because we had 4 distinct kits, we decided upon the following 4 locations locations:  RED – sidewalk in front of our house, cobblestone area of our driveway, the asphalt road in our community, and the concrete surrounding the pool deck.  BLUE – our lawn, beneath the roses in the the landscaped area of our house, in the shrubs across the road from our house (pictured below), and in the backyard.  
I then  asked the kids to write out their prediction or hypothesis.  “Where do you think we will collect the most ants?”  Both of the kids predicted we would see the most ants in the backyard.  “Ants make their homes and build colonies in the dirt, so I think that is where we will find them.” As it turned out, this wasn’t how things turned out.  

I had divided up the vials for the kiddos and indicated where they should place them.  We then frolicked in the pool for an hour and then proceeded to retrieve the vials.  Surprisingly, only a few vials had any ants.  The vials we placed at the pool were inebriated with tiny little ants … so many in fact, crawling every which way … that I had difficulty putting the lids on and many escaped our capture as a result.  

When the kids returned from the other areas where they’d placed the vials, I discovered that several vials were completely empty … there wasn’t even any cookie crumb (or whatever it was that had been placed in the vials to attract the ants). Come to discover that my little guy had inadvertently dumped out the contents.   
After several interrogations, he insisted that he placed the vials on the ground with the food but it was upon the return that he dumped them out.  “There weren’t any ants so I didn’t think about it,” he said.  Ah well.  Our mistake provided good points of discussion for our conclusion when I asked, “If you were to do this experiment again, what would you do differently?”

“The School of Ants project is a citizen-scientist driven study of the ants that live in urban areas, particularly around homes and schools. Collection kits are available FREE to anyone interested in participating. Teachers, students, parents, kids, junior-scientists, senior citizens and enthusiasts of all stripes are involved in collecting ants in schoolyards and backyards using a standardized protocol so that we can make detailed maps of the wildlife that lives just outside our doorsteps.” 

For more information on studying insects with children, check out this Squidoo lens:  Bug Collecting.  It was awarded a Purple Star!!  

Update 28 Aug 2012 –  The species we found was identified as the Argentine Ant (Linepithema humile).  Check out what species were found across the country by following this link,  School of Ants – Result Map.

Pipevine Swallowtail :: Summer Nature Study

On Saturday morning, we went for a little walk along the Tower House Trail in Whiskeytown National Recreation Area.  We had didn’t know what to expect but we’d hoped to observe dragonflies for the August Outdoor Hour Challenge.    Though we did observe a few from a far, what we discovered was much more alluring.

The munchkins and I were immediately intrigued.  I had never before seen a caterpillar quite like this one in the states.  As we observed their behavior, I was reminded of my weeks in Ecuador as part of an Earthwatch Expedition, Rainforest Caterpillars.  You can read my post about that experience here.

What struck us was that the caterpillar would extend this ‘Y’ shaped tube from just behind it’s head when it was agitated.  As it relaxed, it would pull it back down.  Way cool!   Covering its body were numerous tentacles (soft to the touch), red and relatively short along the dorsal side and black along the sides of its body.

Upon our return home, we immediately looked it up and discovered they were Pipevine Swallowtail caterpillars.  As larvae or caterpillars, they eat all parts of the plant – stems and leaves both.  As an adult butterfly, they feed upon the nectar of the usual host of flowering plants that attract Lepidoptera.  
As per usual, the munchkins wanted to bring them home to watch them change into a chrysalis and eventually emerge as a butterfly.  As we’ve just moved, I was not prepared for this and managed to convince that we would consider this for next time.  

Aquatic Critters :: Summer Nature Study

We’ve been going to Indian Mary near Grants Pass every 4th of July holiday for nearly 15 years now. Each year, I spend a little time picking up the rocks along the shore and investigating the invertebrates that cling to the rocks. The past couple of years, since we are now “homeschoolers” we have gotten a little more scientific about our search and bring along tools for collecting. I hadn’t previously considered documenting our findings until this year.

rogue7Searching for aquatic critters is one of our favorite summer activities. The kids spent hours along the river rubbing the rocks to see what critters might fall off into the dish pan. We then carried this back to the campsite where we could sit in comfort of the shade to observe our specimens more closely.

In past years, I’ve always seen a number of dragonfly, mayfly and stonefly nymphs. Planaria worms have also been prevalent.  This year however, I didn’t find a single planaria and instead found numerous midge larva and leaches!  Quite a surprise.

Additionally, we discovered many translucent little gel-like bubbles attached to the rocks as well as a couple of white tissue-like cocoon shapes (shown below).  I am not certain what these are, however.

We pack along a few reference materials with which to identify our discoveries and to learn more about each specimen. Click on this link, A Guide to Aquatic Insects, for a free excerpt from Science Logic: Ecology Explorations.  Using these references, the kiddos and I spend some time sketching and taking notes in our nature journals.

As I shared our discoveries with friends and family with whom we were camping, it was brought to my attention that a notice had been posted near the restrooms that a health concern regarding the portability of the water had been issued due to the water turbidity.  Turbidity is the cloudiness of a liquid caused by individual particles or suspended solids that are generally invisible to the naked eye, similar to smoke in. The measurement of turbidity is a key test of water quality.

Using another key test of water quality, I was delighted that we had determined this for ourselves!