A midwinter's feast

During the fall, I would frequently check on the crabapples to see if anything was eating them.  However, back then, they did not appear to be appetizing to anything except coddling moth caterpillars.  Finally, now that it is the middle of winter and there is very little else to eat, the crabapples are attracting more interest.

Crabapples, some partially eaten, covered in frost after a freezing fog.

Over the past couple of weeks, I have seen large flocks of birds, including house finches (Carpodacus mexicanus), occupying the crabapple tree and eating the fruits.

A female house finch (Carpodacus mexicanus) picking a crabapple.

The birds are messy eaters and have littered the ground below the tree with bits of fruit.  These bits, in turn, have been attracting flightless consumers: rabbits, rodents, or both.  Nevertheless, the crabapples are not the top choice for all the animals visiting the yard.  When a flock of cedar waxwings (Bombycilla cedrorum) appeared this weekend, they ignored the crabapples and feasted on the many juniper berries that had also been left uneaten since last summer.

* To see this video in high definition (1080p), you may need to (1) click "YouTube" to watch on the YouTube website and (2) change the settings at the bottom of the video screen.

The secret to staying green

While admiring the fall foliage on the crabapple tree, I noticed that some of the leaves still had patches of green, whereas others had turned a uniform yellow.

A crabapple leaf with three green patches.

When I flipped these leaves over, I found a clue to why the patches were staying green.  Wherever there was a green patch on the top of the leaf, there was a matching mine of a tentiform leaf miner on the underside of the leaf.

Three tentiform leaf miner mines on the other side of the crabapple leaf.

Below is a close-up of another mine.  As the leaf miner feeds, it separates the layers of the leaf.  The surface layer then dries and contracts, forming wrinkles on the bottom of the leaf and a tented shape on the top of the leaf.

It seems quite convenient for these leaf miners that the patches they are eating remain nutritious, even as the leaves are senescing everywhere else -- but how does this happen?  Fascinatingly, a study has found that it is bacteria (living within the leaf miners) which are responsible for producing these "green islands" and that they do so by manipulating the plant's own hormone signalling.

Explore some more: Plant green-island phenotype induced by leaf-miners is mediated by bacterial symbionts

One rotten crabapple

As the crabapple fruits have ripened, they have turned a brilliant red.  They are still not edible, but they have brought a welcome splash of color to the garden at a time when most of the plants are fading.

The ripening crabapple fruits have turned bright red.

Although I think that the fruits are too sour to eat, the taste has not proved an obstacle to all.  Some of the fruits, such as the one pictured below, have holes filled with insect frass.

A crabapple fruit with a hole filled with insect frass.

I wanted to see what was eating the fruits, so I picked the one pictured above and sliced it open.  At first, all I found was more frass.

A crabapple fruit filled with insect frass.

However, after I carefully sliced more of the fruit away, a small caterpillar came wiggling out.  It was a codling moth (Cydia pomonella) larva, a major pest of apples that also attacks the fruits of other trees including crabapples, pears, and walnuts.

The codling moth (Cydia pomonella) larva that had been eating the crabapple.

Saved by the camera

I was standing near the crabapple tree when a dark shape on one of the leaves caught my eye.  As I moved closer, I saw that there were actually two dark shapes -- a parasitoid wasp and a jumping spider. 

A jumping spider sneaking up on an ichneumon wasp.

The jumping spider was stalking the parasitoid wasp, which was preoccupied with laying an egg.  With the spider poised to strike, I thought the wasp had no chance to escape.

The jumping spider closes in on the ovipositing parasitoid wasp.

Mysteriously, though, this was as close as the spider got.  After looking at the wasp for a couple of seconds, the spider abruptly turned and moved back down the leaf.  Perhaps it was spooked by the camera, or perhaps the wasp was simply too large for the spider.  Meanwhile, the wasp continued laying its egg.  A couple of minutes later, it turned to face the site where it had been laying an egg or eggs, then spent some time apparently chewing.

The ichneumon wasp chewing nearby its oviposition site.

Once the wasp had flown off, I turned the leaf over to see what had been parasitized.  What I found was the mine of a tentiform leaf miner, with a hole where the wasp had been facing.

A tentiform leaf miner mine with a hole (on the left) where the wasp appeared to be chewing.

Surprise inside

Earlier in the year, the crabapple (Malus sp.) tree in the backyard was buzzing with bees.  Now, it is covered in small, sour fruits.  I keep checking the fruits to see if anything will eat them, but so far they have been left alone.  Instead, I have noticed that many of the crabapple leaves are getting rolled up and eaten.

A rolled crabapple (Malus sp.) leaf.

Curious to know what was inside, I began carefully unrolling the leaves.  Within the first few leaves I found white silk, insect frass (the black droppings in the picture below), and ladybugs.

A convergent ladybug (Hippodamia convergens) in a rolled crabapple leaf.

However, most ladybugs are predators, not herbivores.  Something else must have been rolling and eating the leaves -- and then been eaten by the ladybugs.  I kept looking.  On about the fifth leaf, I finally found a leaf roller caterpillar.

A leaf roller caterpillar inside a crabapple leaf.

Having found only harmless (to me) insects inside the leaves, I started unrolling the other leaves with less caution.  However, I soon discovered that the leaf roller caterpillars were not the only ones rolling leaves.  As I peeled open another leaf, I saw long, spindly legs -- and I immediately released the leaf.  I brought a flashlight down to the garden so that I could peek inside through the narrow opening without further disturbing the leaf.  With the aid of the flashlight, I found that the legs belonged to a spider guarding its egg sac.

A spider and egg sac inside a rolled crabapple leaf.