Sunday, July 01, 2012

Six-legged tigers

A couple of days ago, I went over to the vacant lot again, to check on the ant nest (of which, more later). It's been raining off and on, so the puddles are still there, but they've shrunk to about half the size they were a week before. The first one is barely an inch deep now, in the deepest part.

I was crouched over this puddle, trying fruitlessly to get a photo of a fast-swimming black bug, when I noticed what looked like a small fish. At least, it was long and streamlined, and moved like a fish. I abandoned my frustrating bug and went fishing with a small bug-collecting bottle.

The "fish" was also fast, but it attempted to hide in the loose mud at the bottom, and I was able to scoop it out, mud and all. In the bottle, it looked more like a miniature lizard:

Mini lizard with 6 transparent legs? 1/2 inch, jaws to tip of feathery tail.

When I released this one back into the puddle, I saw another, double the size. Too big for my bottle; I chased him all over the puddle with the camera instead.

6 hairy legs, a two-pronged tail, and a pair of sharp-looking hooks in front.

Later, when I looked them up, I learned that they are water tigers, the larvae of the Predatious Diving beetle, which may have been the black bug I was chasing at first. I'll have to go back again and actually catch one to be sure.

These beetles, adults and larvae, can be found in almost any body of water. The larvae hatch from eggs laid inside the stem of underwater plants. Or, in this case, in the stems of plants that at least for a while were underwater. Some live as larvae for up to a year, but in temporary ponds and puddles, they may mature in a few months. When they are ready, they crawl up onto land, make a burrow in the mud, and pupate there. After a week or more, they hatch and return to the water as adults.

Both adults and larvae are air breathers, although they live in water. The adults are scuba divers; they bring their air down with them, holding bubbles under their wings. The larvae breathe through the tip of the abdomen, holding it up just above the surface, but can go a while between breaths.

Two small water tigers. One is breathing; his abdomen tip and the two prongs of his tail are out of the water.

Tigers. The name gives a hint as to their habits; they're voracious predators, able to stalk and kill other insects, small worms, tadpoles, and even fish. And then, there are the defenseless smaller residents of the puddles; they'll take them, too; easy pickings.

Returning to the story: the big water tiger I was following stopped for a meal. The puddle is still as full of ostracods as ever; you can see some resting in the sediment in all three photos above. But here and there they formed clumps or heaps. And the ostracods in these heaps were dancing about like bubbles in a fast-boiling pot. Or like the mating snails on Crescent Beach.

A small clump of happy ostracods.

The water tiger meandered here and there around the puddle, not in any hurry, stopping occasionally to look around. Eventually, he found one of the ostracod gatherings, and dived in headfirst. He dug around for a minute, selecting or trapping one, then turned and sped off with an ostracod in his jaws, to eat it elsewhere. I chased him, trying for a photo, but now he was in a great hurry, in no mood to share his meal with any other water tiger, nor with the shadow above him. I soon lost him.

Selecting the juiciest, fattest ostracod. Tail on the surface, head in the grocery bin.

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1 comment:

  1. Fascinating---thanks for the great post!

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