Thursday, June 14, 2012

Waiting in the wings

It's easy to get the impression that insect or arthropod life explodes in mid or late summer. For instance, if we haven't been paying close attention, it seems like suddenly in the heat of summer our yard is filled with big golden garden spiders, Argiope aurantia.

They are formidable hunters, sitting on their zigzag stablimentum in the middle of their web. If they feel the vibrations of a large animal, such as you, approaching, they begin violently jerking back and forth, in order to attract your attention to their presence. You, or a dog or a cow, will much prefer to walk around them to getting caught up in their nasty sticky web, and they much prefer not having to remake it. Before long they will be catching your favorite dragonflies or butterflies. They often catch and eat tree frogs and occasionally catch hummingbirds (which we rush to rescue). We're fond of our spiders, but sometimes move an Argiope out of a very rich butterfly area to a quieter spot.

But the point is: Where do they all suddenly come from?

Well, they were all there to start with, but they were in their early tiny forms staying out of sight low in the vegetation. If you watch for them, in the spring you will begin seeing a white circle about the size of a nickel deep down in the grass. This is the early form of their stabilimentum, woven so densely it is opaque. If some little predator comes by, the spider can flip around to the other side in an instant to be out of sight. As the year progresses, the circle gets more tightly woven and bigger until, after a certain number of molts, the zigzag begins to develop. Here is the progression I have seen so far this year.

But spiders aren't going to be the big news this year. The signs are already here. When you walk through grassy places, or flower beds, you hear a skittering ahead of you, and see the movement in the vegetation, as if someone were scattering small gravel. It's grasshopper nymphs. Grasshoppers don't have a full metamorphosis. They come from the egg as tiny grasshoppers, more or less like the adults, but without developed wings or genitalia. With each molt they look the same, only larger. They still are only that skittering in the grass (though Cheryl complains they are eating her flowers). Here are a couple of nymphs that with a few more molts will be large and voracious Differential Grasshoppers, with long wings for powerful flight, powerful chewing jaws, and judging by how many I am seeing now, they will be in destructive numbers.

It is not until the last one or two molts that suddenly they become visible, large eating machines. Agricultural entomologists are predicting plagues this year. It will be a problem for farmers, who will need to defend their crops. But in a way it will be a boon for me, as I am studying grasshoppers this year, and it will certainly be a boon for the Argiopes, who feed heavily on large prey like grasshoppers.

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