Milkweed aphid population explosion

One of the swamp milkweed clusters in the backyard is infested with aphids, in particular the milkweed aphid, Aphis nerii.  The population density is so high that you can hardly see the stem or the pod for all of the aphids covering it.

They have clustered on the tips of almost every pod and new stem.  What you see in the photo are their balloon shaped abdomens sticking up, while their heads are down with mouthparts probing into the plant sap for the sugars being transported to the developing seeds.  Those two black projections are not their legs, but cornicles that secrete a defensive, waxy fluid (see large aphid on top left center below).

Large population densities like this attract a variety of control agents.  Two of the major predators on the aphids are ladybird beetle larvae and syrphid fly larvae.

I found several of these ladybird beetle larvae near the clusters of aphids.  This one (above) was happily munching away on one of them.

This is the larva of a syrphid fly about ready to pupate.  It’s about one-half inch long and has become rather immobile at this point.  But they are quite active when hunting aphids and readily just mow them down.

A third potential predator may make an appearance soon.  These are lacewing eggs, and the larvae that will eventually hatch are aphid specialists.  These are the bugs you really want in your garden.

The larvae of the Green Lacewing look like this.

Green Lacewing larva attacking an aphid from Wikipedia

By far the greatest damage to the aphid population probably comes from the parasitic wasps that patrol the colonies.  These tiny (one-eighth inch long) wasps crawl over, under, and around all of the aphids, probing them with their antennae and then sticking them with their ovipositor at the tip of their abdomen.

The wasp injects a single egg, which hatches inside the aphid body, and the wasp larva then consumes the aphid’s organs turning the aphid into a brown to black ovoid husk (center of photo below).

Aphis nerii are parthenogenetic, which means that they are all female, and produce clones of themselves by self fertilization.  There are no males of this species in the U.S., and thus no sexual reproduction.  They are also viviparous, giving birth frequently and to many offspring at one time.  If you watch these aphids long enough, you can see the tiny yellow blobs emerge from one of these very swollen yellow bellies.

When populations densities get this high, or when the food supply becomes exhausted, many of the aphids will develop wings to disperse to new feeding areas, where they once again undergo a rapid population explosion.

Pine Squirrels – West vs East

While walking on the Tahoe Rim Trail late one evening last week, I spied a Chickaree, or Douglas’ Squirrel on a rock up ahead of me.  It was busily husking seeds from a pine cone and took off before I could get much of a photo of it.  John Muir, founder of the Sierra Club, and noted Sierra Nevada conservationist, thought this particular animal was one of the “most enchanting” and interesting to watch.

Although I didn’t get a chance to observe those enchanting behaviors, I got a good enough look to realize how similar this western Sierra version is to its cousin, the Red Squirrel, we see in the eastern US.

(I took this photo of a Red Squirrel in my backyard last December.)

Both species are about half the size of the common gray squirrel, but twice as feisty.  In fact, they are so aggressive, they chase the larger squirrels away from their favorite feeding sites.

Both species favor the cones (and seeds) of pine and spruce, and prefer to husk the cones when they are still green.  Both have that distinctive white eye ring, and both curl their tails over their back while sitting (probably keeps them warmer).  Since both species lack cheek pouches in which to store seeds, they bury the entire cone instead and harvest the seeds as they need them.

Like the other tree squirrels (Gray and Fox), these squirrels do not hibernate in the winter, but sleep the winter away in a cozy tree hole.  The stockpile of seeds usually lasts them well into the spring.

Here’s another look at the video of Red Squirrels harvesting pine seeds that I posted last December.

The Color of Birds: pigments

There have been a couple of questions recently about how color is controlled in bird feathers, so I thought I would explain that with some examples from some of my bird photos.  One excellent explanation of coloration in bird feathers can be found at the Cornell Lab of Ornithology’s website:

To summarize their information, the color of bird feathers is formed in three ways:  by pigmentation of the feather, by structural properties of the feather, or a combination of both.  This post is about just the pigment part of color production.

There are three basic contributors to feather pigmentation:  melanin, carotenoids, and porphyrins.

Melanin pigments give feathers a yellow-brown to black appearance, the density of color depending on the amount of melanin present.  The presence of the melanin or any pigment actually strengthens the feather, and so we often see birds with white wings and black wing tips (e.g., gulls, terns, and white pelicans).  However, melanin also makes the feather more susceptible to bacterial degradation, leading to frayed wing tips which are not good for the long distance flyers or aerial maneuvers.

White Pelican from Lac Qui Parle dam, Minnesota.

Carotenoids may be derived from plant compounds like the xanthophylls we see in yellow, orange, or red leaves in the fall or carotene we see in carrots.  They must be eaten by the birds as the feathers are growing in during a molt, and some are modified by the bird to produce a specific color.  Examples are the yellow of Goldfinches or the yellow and orange colors in some tropical tanagers and spring warblers.

Flame-colored Tanager in Boquete, Panama

Porphyrins are metalo-proteins synthesized from amino acids, like the heme protein in the hemoglobin of our red blood cells.  These pigments produce pink to red colors, and in combination with melanin pigments produce the rich reds, brown, and greens of some tropical bird species, as well as owls, pheasants, turkeys, and other fowl.

Male Quetzal in Bouquete, Panama.


What pigments produced the color in this Keel-billed Toucan?

Another scary-looking, big, black wasp

Rabbit Brush was in full bloom at Spooner Lake on the east side of Lake Tahoe, and several pollinators were busily working the plants.

  One I thought I recognized turned out to be something else entirely.

It looked like the Great Black Wasp, with an orange abdomen instead of a black one.  But it seemed even larger than the Great Black Wasp!

This is a member of the same family (Sphecidae) as the Great Black Wasp, but a different subfamily, the thread-waisted wasps.  The “thread waist” is that skinny segment between the winged thorax and the orange abdomen and is characteristic of this group.  After much looking, I think I can say that this is a species in the genus Ammophila, but there are 200 species in that genus, each of which can be highly variable in the amount of coloration, length of segments, etc.

“Ammophila” comes from the Greek root meaning “sand lover”, which is a good descriptor of its habit of building nests in sand.  Like other hunting wasps, it grabs prey with its strong forelegs, paralyzes them with its sting, and carries them to the nest.  The prey are most often hairless caterpillars.  It then lays one egg on the caterpillar and seals the nest, using its strong jaws to hammer a soil plug into the hole.

Note the extremely long, spiny forelegs used to carry prey to the nest.

Nest provisioning of the grub is done on demand, as the prey is consumed.  The wasp remembers the location of each of her nests, unseals them at intervals to check on the development of her offspring, and then brings additional prey as needed, resealing the nest after each delivery.

Who said insects had little brains?

Sooty Grouse in the backyard

I stepped outside the door to go hiking on the Tahoe Rim Trail near sunset, and ran into a family of Sooty Grouse (hen and four young).  For those who know their birds, these used to be called Blue Grouse, and they do have a small amount of blue showing on their breast feathers.  But overall, this bird does an amazing job of blending into its coniferous forest floor background.

Mother hen led her offspring across the road and up into the forest.

Note how well the young grouse blends into the background.

Sooty Grouse live in montane foothills, near the coniferous border, and range from northern British Columbia along the coast to northern California and all along the Sierra Nevada mountains.  They are permanent residents where they occur, but have the strange habit of actually going to higher altitudes in the winter (contrary to most other species).  They are quite omnivorous in the summer, eating a varied diet of insects, berries, and leaves, but in winter they subsist on a diet of Douglas fir, hemlock, and pine needles.  In order to balance their winter energy budget on such an indigestible diet, their gut elongates and they grow a large fermentation chamber in the part of the gut analagous to our appendix (theirs is called a cecum).

To maintain their cryptic coloration in the winter, their newly molted feathers are a grayish white color, so they blend nicely into the winter snow.

In the spring, the male molts new, bright brown and gray feathers, and develops brightly colored vocal pouches on either side of their neck which they inflate while spreading their tail and parading in front of the female.

photo from Avian Web

Begging Jay

We stopped for a snack while on our walk on the Rainbow Trail along Taylor Creek. A Stellar’s Jay discovered us and stopped to see if we would leave something for him.

They normally eat a varied diet of insects, seeds, nuts, and berries.  They are unpopular for their nest thievery, because they will take eggs out of unattended nests and even grab unprotected nestlings as a snack.  But today this one was interested in our peanuts.

This is an entirely western species, and in fact, replaces the eastern Blue Jay in about the middle of the Rocky Mountains.  Their range stretches from northern British Columbia along the western one-third of North America as far as Panama, but they are usually found at elevation in coniferous forest.

I love their bright blue color, which as you recall from an earlier post, is created by the light reflection within the feather structure, not by a pigment.

The bays of Lake Tahoe

On the opposite side of the lake from Emerald Bay (see last post) is another beautiful bay called Zephyr Cove.  This might be the prettiest area in the Lake Tahoe basin.

Chipmunks and ground squirrels run throughout the pine forest that lines the shore, and I caught one Golden mantled Ground Squirrel doing a little construction on his home.  He had a huge hole, from which he began removing excess dirt.

First he scoped out what needed to be done.

Then he dug for several seconds with the front feet (see spray of dirt there).

Then he moved the dirt out of the hole using his back legs.  This was repeated several times, but the sand was so loose, it just slid right back down the sides of the hole.

Golden-mantled Ground Squirrels are slightly bigger than the Western Chipmunks, and are quite adept at feeding on whatever is available:  insects, berries, seeds, nuts, even underground fungi.  Like other ground squirrels and chipmunks they hibernate for most of the fall, winter, and spring, taking food with them to their overwintering burrow.  Around Lake Tahoe they are fairly tame and will come investigate any food scraps campers leave behind.

Beautiful Lake Tahoe

This is the prettiest lake in California (in my opinion).  Here are several views taken over the past two days.  I did not Photoshop the color!  Hover your mouse over the photo to see where it was taken.

For those who have not visited this scenic wonderland, Lake Tahoe is located on the border of Nevada and California at 6200 feet elevation.  Filled primarily by the Truckee River runoff from the snowpack on the Sierras, the water is exceptionally clear and exceptionally blue.  It is the second deepest lake in the U.S. (1645 feet), and the largest alpine lake in North America.  It was formed about 2 million years ago along with the rest of the Tahoe Basin, at the end of one glacial period.

Blue-eyed Bug-eater

While walking the shoreline of Pyramid Lake (and taking photos of grebes) the other day, I found a number of beautiful pebbles that looked like they had washed down from Wonderstone Mountain (about 60 miles away; they weren’t from there, they just looked like it.)

I reached out to pick up yet another pretty red pebble, when it moved.  It wasn’t a pebble.

A closer look with the telephoto.

This is a White-belted Ringtail dragonfly, and its coloration certainly makes it distinctive.  It seems to be widespread in the western U.S., where it favors stream habitats with fine sediments, but is threatened in many locations because its habitats are being degraded or disappearing.  Other than some beautiful photos of this handsome insect, I could find no information on its natural history.

There were a few flies on the beach of this pristine desert lake, and the dragonfly was in no hurry to leave so I kept shooting photos.  I particularly liked the big blue-eyed goggles it seemed to wear.

Pas de Deux of the Western Grebe

Yes, they really do dance, just not today.  Instead, there was a display of pair swimming and head tipping back and to the side first in one bird and then in the other while facing each other.

In the spring, at some point during this courtship ritual, both birds rear up on their toes and patter across the surface of the water in perfect synchrony, as shown in the video below.

However, a little love play in the non-breeding season helps keep the pair together for the next breeding season.

Western Grebes are the largest of the North American Grebes, weighing 2.5-4 pounds with a 30-40 inch wingspread.  They nest in colonies of hundreds of birds on inland lakes, like this one (Pyramid Lake in western Nevada).  Northern birds like these will migrate to the coastal ocean for the winter.