Tuesday, January 14, 2014

More winter invertebrates

More freezing, more pounding rain, and then the sun comes out, it warms up a little, and I step out in the backyard. I check the leaf litter, I check the walls of the house. There is life.

First, a rustle in the leaves. I look down at my feet, and this time I don't see just some little dot, it is something big, over two inches long. It is an American Bird Grasshopper, one of the largest and handsomest of our species.

They are out every month of the year, even January, if the day is mild. They eat grass, and there's always some grass somewhere, and they must have a way of getting through real cold weather, sheltering somewhere. It is a common experience, even on a sunny day in midwinter, to flush one from the undergrowth and have it fly off in a direct line twenty or thirty feet, then land in a tree about ten feet off the ground. It's the large size and the powerful flight that gives it the name bird grasshopper.

There were also a few flies around. Flies, for all their fragile appearance, seem to be the commonest group of insects active through the winter. I saw, for instance, the usual Winter Crane Flies, and I saw another (or maybe the same) Tachinid fly that I had photographed for an earlier winter blog. And here was another fly that we regularly see in winter, especially in our house.

This, I believe, is the Northern House Mosquito (Culex pipiens). It can be a vector for West Nile Virus, but not at this time of year, when I don't believe it is biting. Male mosquitoes feed on plant juices, and probably females (like this one) do too, but when females are developing eggs, they need protein, which they get from a blood meal. But at this time of year they aren't mating and egg-laying, they're just waiting out the winter. Adult mosquitoes of other genera such as Aedes don't survive the winter. They lay eggs singly in low places that will be flooded in the spring, and the various species overwinter in the egg form. When the low spot fills with water, and when the surface tension in the water weakens a bit (indicating that plant material is beginning to decay, which provides food for the larvae), the eggs wake up and begin developing. The House Mosquito, on the other hand, lays a raft of eggs on the surface of the water, something it can only do in the summer, since ice would kill the floating eggs. So this mosquito hibernates not in the egg form, but in the adult form, seeking sheltered places to overwinter, which is why we often find them in our house at this time of year. This one was on the wall of my garage.

They of course are common, in fact commoner than we like, but the next fly I saw was a bit more special. It was a very small reddish fly that didn't look very interesting, and I just took a quick snapshot of it, not being very careful, and so getting sort of a blurry picture.

I took a second quick picture more from the side, and then I saw in my viewing screen the fly was more interesting than I had thought, but before I could take a better picture, it flew away.

I got out my huge tome, Flies: The Natural History and Diversity of Diptera, by Stephen A. Marshall, (2012) and looked it up. It was in the family Heleomyzidae, in the genus Suillia. It had, among some other interesting features, the outer margin of the wings armed with sharp spines, as you can see in this blow-up (and here is where I wish my pictures were sharper):

I didn't see any explanation for these spines, but generally this sort of armament on the leading edge of the wings (there are some similar cases with butterflies) is for battling other members of their own species over mates or territory or food sources.

As for spiders, the usual one was out, Pardosa milvina. There is scarcely a day I can't find one, but now suddenly they have greatly increased their numbers, and when I walk along over the fallen leaves, the little black dots of their bodies are streaming away from me. I can see six or eight at a time, almost up to spring numbers.

Note the long right-angle spines on the two hind pairs of legs (sign of genus pardosa), and right in the middle of the abdomen the two side-by-side pale spots (sign of the species milvina).

There was one more creature out on the day that I saw all of these. It was the size of a dot with legs like threads radiating out from it, so that the whole was about half an inch in diameter. Some kind of baby spider?  I used my digital magic to take a close-up picture then download it onto my computer, then blow it way up on my computer screen.

Not a spider but a spider relative, a Harvestman, so tiny it must still be the size it was when it came out of the egg.  But it had already managed to lose one of its hind legs, though it would molt its skin enough times to regrow another one. These, like the unrelated crane flies, are also often called daddy-longlegs. Like some crane flies they can also get quite big, 2-3 inches across with their legs spread out. Here's something to notice about them, if it has never been pointed out to you before: They don't  have antennae ("feelers") like insects, instead they use their second pair of legs like antennae. If you look you will notice they are much longer than the first pair. The next time you see a harvestman, watch it walk, and you will see it sweeping its second pair of legs over the ground ahead, like a blind man with his stick.

So, a little bit of life to cheer me up through the long cold days ahead. I think it's appropriate then to sign off with this happy-face bug (Banasa euchlora) I just saw crawling up the outside of our front door.

Sunday, January 5, 2014

Postscript to Winter Invertebrates

There are some very small spiders (2.5 mm) out there that are so numerous they can create effects which you can see from a hundred feet away. Though you can barely see them, they can half fill the sky and the ground before you with their works.

Here's one, the Money Spider (Walckenaeria directa):

Here's another, the Scarlet Sheetweaver, (Florinda coccinea):

Here it is on Cheryl's finger nail to give you a better sense of the size.

The large visible (and often quite beautiful) effect they achieve depends upon the ability of probably millions of tiny creatures over a large area to magically coordinate and synchronize their activity. It's the kind of show that nature is so good at putting on.

Every few years late in the year, usually October or November, when conditions are just right (which means gently rising thermals) members of the large family Linyphiidae (the Dwarf Sheetweb Weavers) such as those pictured above, get out on the end of a twig, stick their butts up in the air, shoot out a few inches of web, and when the rising air picks up the web, the spider lets go, and is carried aloft. This is a standard operation for small spiders; it's called ballooning. They can't fly like insects, so they have developed this very efficient way to move great distances swiftly and effortlessly, and separate themselves from their siblings and find their own territory. What is different here is the number (millions) and the timing (all at the same time). A few hundred or thousand feet up their lines begin to tangle with the lines of others, and as the breezes whip them around the webs are self-woven into large cottony sheets. If you happen to look up in the air with your binoculars, you see the sky is half filled with these pure white skeins, that keep conglomerating into larger and larger sheets, six feet long or more. And then as the rising currents diminish they drift down and stick to telephone lines or cars or bushes or tall grass. (People with absolutely no souls may think it is a big sticky mess.)

We have seen this phenomenon (the dense webbing is called Gossamer) every few years around the Jonesboro area, though we have never studied it closely. But now we are studying spiders, so we hoped against hope we could finish 2013 with a big Gossamer year.

October passed, and no Gossamer. November passed the same. Finally December was over and all we could do is give up.

January 1st of 2014 we were driving dirt country roads in Lawrence County up past Pocahontas. Ponds were frozen over, skins of ice were along the edges of streams, for the past week temperatures had been below freezing every night. We came around a bend and saw the grass tops on the levee road above us shining white.

I had driven up onto the levee to photograph it (even though it was inside someone's property). Cheryl, waiting down on the road below outside the farm, said "Here comes the farmer fast in his pickup." I thought I would have to do some explaining, but in fact he was interested. "Where does the gossamer all come from?" He even called it by that name. He said it was all over the place, and we would see more of it along the road farther on down.

This  picture is from the next patch. It was a bit more sheltered from the beating wind which had made photography impossible up on the levee.

Here's an example of how dense it is. It looked like tightly woven sheets, yet I think it is the single lines of multitudes of ballooning tiny spiders tangling together in the air, literally self-weaving.

And it was teeming with spiderlings (note the little seed-like dots).

All kinds of spiders. These are young wolf spiders.

A mixture of money spiders and others.

A male Scarlet Sheetweaver, one of the main perpetrators of these skeins.

The money spiders are another.

But many spider species just seemed to be along for the ride, perhaps out ballooning on their own when they were caught up in the mass. The larger spider in the foreground is a young Striped Lynx Spider.

An assortment of wolf and money and other spiders.

 It looked like the main fallout had occurred a day or more ago, but they seemed to have survived the freezing temperatures. It was a nice way to finish the (slightly extended) last day of our first year (2013) of studying the spiders. And of course a nice first day of the 2014 spider season.