Sunday, August 25, 2013

Black Swallowtail Butterfly Larvae on Dill

If you have ever found caterpillars on your dill plants in your garden they are almost certainly the Black Swallowtail Butterfly caterpillars like the ones seen in these pictures.  My son found these on his dill. 

Black Swallowtail Butterflies lay their eggs exclusively on plants in the carrot family.  In the wild in this area that means Golden Alexander plants, and, south of Minneapolis, Queen Ann's Lace.  In your garden it means dill, parsley, and carrot.

The caterpillars eat the entire dill plant, right down to the ground.

 Butterfly and moth catterpillars all grow through what are called 5 "instars" or growth stages.  With each new instar the caterpillar sheds its skin and is able to grow larger.

In each instar the larvae usually look a bit different, or maybe a lot different.

This picture is of the 3rd instar for the Black Swallowtail caterpillar.  It is preparing to shed its skin here.  It quietly sits still on the plant stalk for several hours, not its normal behavior.

Notice all the spines and tubercules on the caterpillar's back.  These will get smaller with each instar until they are not present in the 5th or last instar.

Also notice the white 'saddle' in the middle of the back in this picture.  This will disappear in the next instar, as can be seen in the picture below.

Notice also the silk threads the caterpillar has woven all around the stem so the old skin will stay attached as it splits and the 'new' caterpillar moves forward.
 Here the caterpillar above has just shed its skin.  Basically it just crawled out of it during the night time.  The skin fell off the stem before I could reposition the camera for a better angle.
Here is the caterpillar in the 5th and final instar.  All the spines and tubercules are gone now, and the caterpillar uses its colors to blend in and not be seen by predators.

The caterpillar is about 3 inches long here, 3 times the length it was in the 3rd instar, which is the 2nd picture above.

It is pretty easy to see the difference between the six 'true' legs up by the head and the 10 'pro-legs' or 'false' legs that protrude from the caterpillar's abdoman.

These false legs are like little velcro pads that stick to plant surfaces very well, enabling the caterpillar to use the true legs to help grab and pull food towards its mouth.
 Here you can see the sharp edged 'jaws' pulling in the dill flower, along with a lot of pollen that has stuck to its face from all the other flowers it has eaten in the previous day.

I don't think these caterpillars help with fertilization of the flowers since they completely eat every flower, and stem, they can find.

Notice the aphid trying to escape at the bottom of the flower stem.  I didn't notice the aphids until after I was looking at the pictures on the computer. 
 It soon became obvious that every flower had its group of aphids that were soon to be deprived of their home and food as the caterpiller ate it all. They were very tiny, and trying to figure out where to go. 

The caterpillars seemed bothered by  the aphids when they crawled onto their bodies, especially when the caterpillars were little.  But I never saw one get eaten, even if it was on  the flower as the caterpillar ate the flower.
 All swallowtail butterflies have a brightly colored scent gland that is flashed out and emits a strong odor when danger threatens.  Black Swallowtail caterpillars are no exception.  But these caterpillars did not seem  threatened by me poking them, so this is the best photo I was able to get.  The orange gland is only about half way out here, and the air was filled with a strong dill/citrus odor.

At about 2 weeks of age the caterpillars start to wander, and after doing this for 12 hours or so, they settle on a plant stem to their liking, and attach themselves with a silk thread as can be seen below.  Now it is ready to transform into a chrysalis, which will appear in an upcoming post.

Tuesday, August 6, 2013

Mantisfly Strange Insect

 I found this Wasp Mantisfly on a flower at Springbrook recently.  It is not a fly or a mantis or a wasp, but is related to the lacewings and similar predatory insects.  It is small, on the head of a Black Eyed Susan here, but fierce looking with a temper to match.

Its colors mimic a paper wasp, but its front legs and head are very mantis like. And any small bug that it catches in its front legs is dinner for sure.

Evolution's adaptive characteristics make for some fascinating creations in nature.   

Friday, August 2, 2013

Aphids Making Gallons of Honeydew

 Ants have taken over a patch of milkweed at the nature center and they have brought their aphids with them.  The aphids cover the bottom side of every leaf, excreting their honeydew, and the ants protect them and get at least some of the honeydew.

It seems very pastoral in theory, but is the most chaotic and busy place around.
 While this picture seems to show the ant gently touching the aphids for a return of honeydew, it is only checking their safety in a very fast pass through the area.

With these aphids the ants don't seem to get the reward directly from the aphids at all.

But look at all the aphids under the 6 feet and legs of the ant.  And this is as big as they get, although there are many very little ones.

I measured the biggest aphids here at just under one millimeter.
 This little part of one leaf underside shows 106 aphids of different size.

The whole leaf had over 1,000, and there were 30 leaves on the plant, which means over 30,000 aphids on each plant.  I counted 22 plants in this group, so over 660,000 aphids in this colony.  Wow!
 Each aphid is withdrawing fluid from the plant, and excreting little drops of honeydew constantly.  Besides producing new babies and shedding their skin that is all they do.

Their drops of honeydew are tiny, but if they added up to just one water droplet in volumn in a week per aphid, that would be 660,000 drops of honeydew per week.  At 27 drops per teaspoon, that is over 7 gallons a week for this colony!

 Here you can see one little droplet just released by this litle gal.  I have turned the picture upside down so it is easier to see, so this droplet would actually be falling up to the leaf below it, onto the topside of the leaf.
 This picture is also turned over to see better, but the droplets are about to fall down, which is up in this picture.

With thousands of droplets falling onto the top surface of the leaf below you can imagine what a sweet, sticky, treasure trove the top of each leaf becomes.
 The ants spend most of their time eating the resulting droplets of honeydew on the top surface of the milkweed leaves.

Here you can see each tiny white spot is a droplet.  The ants get fat eating these, which they can take back to the nest to feed baby ants with.

The ants also have to spend a great amount of time chasing away other critters who are interested in this enormous food source.  They are not very successful.
I counted at least 5 ants on every leaf.  That means there are 150 ants per plant, and 3,300 on the combined 22 milkweed plants at any one time during the day.

But other insects come to feast as well.  There are at least 8 flies that I can count on each plant at any one time.  Lots of them flying all around.

Many are this red eyed species that is house fly size.  Its sponge/mop like mouth is picking up the honeydew, but while it eats even more honeydew rains down from the bottom of the leaf above, covering the fly with little specks of sweet dew.
Several other species of fly are also present, including this larger one.

The aphids are growing on the leaf up above and shedding their skins as they grow.  The shed skins fall as well.  One can be seen under the fly here. It is white.

After a few weeks of this there is mouldy honeydew, fly droppings, shed skins, and anything the wind blows onto the sticky surface.  It is a mess!
Wasps and bees are attracted to the sweets also.  They fly and walk rapidly from leaf to leaf to get the freshest honeydew. But the leaf top is now like a dirty parking lot.  Each white spot is a shed skin that has rained down from above, with much other debris as well.
This wasp has found a relatively clean spot to search.  Its antennae are constantly touching the surface looking for more.
In this picture a different wasp, a paper wasp, is eating the glistening honeydew along the edge of the leaf.

The entire top of the leaf is covered with this coating of sticky food.
Unlike the flies, this wasp is cleaning itself off after feeding for a while. Special combs on the front legs scrape off the other body parts.  It worked for several minutes doing this.

Aphids can be seen on the underside of the leaf to the left.  They are dropping more honeydew to the top of the leaf below.

With over half a million aphids and other food animals present, the predators show up.  Several Ladybugs were hunting and eating aphids while I was photographing yesterday.  The Ladybugs are too big for the ants, but there are so many aphids, they have little impact on their numbers.

This little milkweed patch is an extremely busy ecosystem.  Nothing can compare to it nearby for the  number of insects constantly entering and leaving, not to mention the over half million that live on it every day.