Saturday, November 24, 2012

"The universe in a grain of sand"

When I'm out looking for bugs I am often in a rush. I may, for example, get to a bed of flowers, search it quickly for butterflies, and if I find something interesting, take a couple of photos, then I rush to the next place. Cheryl over the years has tried to teach me that you can sometimes see much more by sitting still and watching the same place for a period of time. If it is not quite a universe in a grain of sand, it may still be an entire complex ecosystem in a square foot.

I made an earlier post, some of you may remember, about sitting and watching the universe of interrelated creatures that met at a road-kill opossum. That's sort of a grim (and stinky) one to recommend to everyone, but here is a much easier and just as interesting one you might try. Some of you can find this one in your garden more easily than you want to: I'm thinking of a plant that is being attacked by aphids. "Attack" might seem too strong a word to use for these bland and brainless creatures that hardly move and spend their day sucking juice out of plant stems. But if you sit still in front of them and watch with your close-focusing binoculars, or better, photograph them from close up with your digital camera, you might be very surprised with all that is going on.

At first all you will see is adults and young ones crammed together bloating up on the sugary phloem they get from the plant. You will at once be reminded of sheep, and wonder how such defenseless things can possibly survive. Well, if you watch them for a while you will discover the main thing they do to survive: They can sit still, not interrupting their constant eating, and pump out live babies all day long, babies that will quickly grow up to squeeze out their own live young, like unending Russian Dolls.

Also it won't be surprising if you see ants walking among them. These are not predators; ants are the earliest pastoralists by millions of years, protecting their herds from enemies, often carrying them from one pasture to another, and even keeping them down in their warm ant nests to get them through the winter. In return, the ants can stroke them with their antennae and receive a drop of sweet honeydew, which can make up an important part of the ants' diet.

But of course all that easy-to-catch and very sweet meat on the hoof is being watched by an amazing diversity of predators. First among them are the flower flies (family Syrphidae). If you watch the flowers that bloom through the year, in addition to bees and wasps and butterflies, you will see they are visited by numbers of bright-colored little flies that are mainly accurate mimics of bees and yellowjackets. Here, for one of nearly a thousand examples in North America, is Syrphus ribesii:

These adult flies drink nectar from the flowers, and are important pollinators. But their translucent and slug-like larvae are major predators of aphids, and if you look closely at almost any aphid-covered stalk of flowers you are likely to find them.

There are three whitish Syrphid larvae in this picture. As you can see in the one on the far left and the one on the far right they have a very specific way of holding an aphid up in the air, and then swallowing it straight down. What is curious here is that ants are tending their aphids, but don't seem to notice these predators. If these had been adult lady beetles (also major predators on aphids), the ants would have attacked them at once and bumped them off the stalk. This next picture shows a different species of Syrphid larva swallowing an aphid down.

In this next picture the flock is feeding calmly, an aphid on the right pumping out a baby, no one seeming to be aware of another wolf in their midst, this one a braconid wasp.

It's selecting a victim.

Now it is pointing the tip of its ovipositor toward the aphid, and will charge it and stab an egg into it.

If you look you will see brown aphids in this picture. They are aphids that are being eaten from the inside by a braconid wasp larva. (The usual mayhem is going on in the rest of the picture.)

When the aphid is completely eaten, the wasp grub will make its pupa inside the hollow husk, and eventually the newly adult wasp will cut its way out. If you come back later in the year you will see a scene like this.

Another possibility is that this pretty little Harvester butterfly might lay its eggs near the aphid outbreak.

The Harvester, you see, is one of the rare butterflies that has carnivorous caterpillars, and they feed entirely on aphids.

Or, if you are watching very closely, you might spot the rather small Aphid Fly, whose larvae are parasitic on aphids.

Or you might see a lady beetle larva, as they are famous devourers of aphids.

The adult lady beetles also eat aphids, and once (only because I was watching so closely) I saw a species of lady beetle new to me that was so tiny it was the size of an aphid, and I got a picture of it eating a baby aphid.

And the predators still go on. Here is a delicate but fierce Green Lacewing, followed by a picture of its aphid-eating larva, and after that a Brown Lacewing and then its aphid-eating larva.

Or you can just go on walking down the path, saying, Well, there isn't much going on today.

(Okay, I admit I had to go out several days over the season to see all of these creatures.)