Nature Trail Tour - August, 2007
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[Additional Tours: February, 2006 | April, 2006 | May, 2006 | July, 2006 | August, 2006 | October, 2006 | January, 2007 | February, 2007 | April, 2007 | May, 2007 | June, 2007 | July, 2007]
The first week of August 2007 brought daily rain showers. One midnight thunderstorm dumped over 4 inches of rain. Rain creates a temporary ecosystem that has much more intense activity than at other times. (Read related essay.) Sibley staff took a walk within minutes of an inch and a half rainstorm, when puddles still stood in the trail. The puddles disappeared within 15 minutes.
Most of the photographs that follow were taken within an hour of the rain. We have inserted a number of links to essays that explain in depth some of what we found
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In a rainwater puddle in the middle of the trail, a kneeling observer noticed the slightly oily sheen to the water, the finely ground organic detritus carried to the puddle (including seeds), and a drowned ant.
This rainbug had been caught by a subterranean predator - a minute later it disappeared underground. To learn more about rainbugs, take a look at this photo essay.
On closer examination, it appeared that small green threads of algae were present within the pale discs. A Crematogaster ant seemed to be investigating the algae. An explanation for the pale discs still was not evident, however. Read this essay to learn more about this species of ant.
Nostoc is a genus of green algae, and some species of the genus form large pulpy masses that look like the "guts" of an animal. It appears during a rainy period. It grows quickly - Sibley staff has never been able to document just how fast - but a mass the size of a cellphone seems to appear overnight. After a day of sunshine it withers to a black crispy object and within another day or two has disintegrated.
Cryptogams turn green with the rain. Read about this essential component of arid land ecology. Tiny honey (huisache) daisy seeds are visible, too.
When looking at the soil closely after a rain, it is almost impossible to see much true "dirt" in an area of cryptogamic soil. A few individual sandgrains are visible (along with part of an old beetle shell), but the soil is more like old leather with the green "leaves" of algae clustered together.
When rain comes down in torrents, the rainwater begins to move across the land, causing "sheet erosion," picking up organic material and washing it along until it lodges against a barrier. Here a mesquite seed had been deposited along with tiny sticks, and the seed germinated because of the several days of rain. The seed had been buried to just the right depth in the soil and organic material for it to germinate.
As sheet erosion occurs, it washes dirt and detritus into rodent holes. This hole might be that of a cotton rat, for cotton rat holes usually enter the ground at a 45 degree angle. This hole had been cleaned out within 45 minutes of the rain.
Normally the native land snails emerge at night, but this one was crawling around at 10 in the morning after the heavy rain. Some of the native land snails live with ants, while others enter rodent burrows. For two or three days after a rain, their slime trails will be visible each morning. Snails eat rotting organic material, and in an arid environment things "rot" only for a few days after a rain.
Earthworms also process organic material (but underground.) As they are most active after a rain, the surface of the soil is often densely speckled by hundreds of "castings," piles of "dirt" that is actually worm "dung."
After a rain, ants "swarm." The virgin queens fly to where males gather (This is another instance of a "lek." Type lek in the search engine to the left to learn what else leks.) The newly mated queen ant returns to ground and immediately begins to dig a new nest. She will begin laying eggs and as soon as they hatch she will never return to the surface. This circle of small soil pellets surrounds her new hole.
Sibley staff did not see the fox after the rain, but it had been on the trail before the staff ventured out to explore 5 minutes after the rain ended. It scratched the soil as it urinated on a grass clump.
A black ground spider ran across the trail after the rain. Sometimes this species is quite common in vegetated areas or in an area with large amounts of organic material, but it was unusual to see it out in the open.
This bee fly rested on the ground. It may have been a male awaiting a female, or a female waiting for ground bees to begin flying again after the rain. The females lay eggs in ground bee holes (and sometimes even on the female ground bee itself) for its larvae eat the eggs of the ground bees.
Moss sometimes grows on the ground after a rain. This was on the trail, in the shade of a tree - in fact, Sibley staff has only found ground moss in the shade of a tree or a mesquite bush, never out in the open. Does moss need the increased fertility that occurs where a tree or mesquite drops its leaves?
Flood detritus was also deposited on cryptogamic soil. Ants often become extremely busy after a rain. New sources of food will be exposed - seeds knocked to the ground, detritus washed into the nest, or material begins to rot in the nest and must be chunked out of the hole.
These harvester ants were busy removing the tiny pieces of organic material that had been washed into the hole and around its entrance. In an hour the entrance was just tiny pieces of gravel. None of the gray gunk in between was left.
This harvester ant investigated what appeared to be worm castings, but might have been soil disturbed by some invertebrate just below the soil surface. Seeds might have been exposed by the activity in the soil. In 15 minutes of observation, this was the only ant to investigate disturbed soil - was this a conscious decision by an individual ant?
This mound of dirt was created by an ant species - possibly the imported or the native fire ant (that is not as aggressive as the imported species.) Seedlings of plants were scattered throughout the fresh digging. A rainbug was not far away, just passing by.