When I was a kid, many years ago, August and September would be the month my parents’ back yard was filled with big orb webs. These webs would have a whitish zig-zag pattern in the middle, and would be occupied by large yellow and black spiders that sat with four legs swept way forward and four legs swept backwards. Looking them up today, they were almost certainly Argiope aurantia (black and yellow garden spider).

Today, my mother’s garden is still host to many orb weavers, but primarily the squatter, orange-brown Araneus diadematus (European garden spider). There haven’t been any of the black and yellow spiders in the garden for years.

Similarly, when I moved into my in West Los Angeles, we would have several Peucetia viridans (green lynx spider) every autumn among the coneflowers, where they would guard a giant egg sac that would hatch out hundreds. We haven’t seen a green lynx spider in the garden for over a decade.

So what’s happened? Have these species been out-competed by the influx of other species? Araneus diadematus are now common in both places, as are Latrodectus geometricus (brown widow spider), neither of which were common before (at least as far as I can remember). Or is it a change in microclimate? Our winters haven’t been getting as cold, and our summers are longer in both places.

It’s strange being old enough to notice systemic change in an environment. In the grand scheme of things, fifty years isn’t that long. But in that timeframe, atmospheric CO₂ levels have gone up by over 100PPM, and somewhere around 85% of all plastics ever produced have been made. Smog levels in the LA Basin have decreased (or at least changed: lead levels are way down, ozone levels are way down, microparticulates are up). These changes may be completely unrelated to the spider situation, though.

In another life, I would have been a nephologist (or more general meteorologist). I have always found clouds, fogs, and mists fascinating.

When I go walking, I tend to look at the sky and wonder exactly what’s going on up there. Are the boundaries of the clouds I’m seeing some threshold of a gradient of temperature, pressure, or moisture content? Why are the patterns the way they are?

One can often see distinct wave action in the atmosphere, but sometimes there will be high-frequency patterns that collide in unexpected ways. There may be different conditions at different altitudes, but in some cases the patterns seem to be at the same altitude.

There are also interesting effects when one layer of clouds (or a contrail) casts distinct shadows on another layer of clouds.

Some cloud patterns look a lot like convection in reverse.

And then there are mysterious places where the conditions just change. For example, the contrail in the picture below. Does it end at some kind of invisible thermocline?

There are a lot of resources for cloud classification and identification online, but I haven’t found as much about the whys of the structure. Some types of cloud structures make intuitive sense. Cumulus clouds sort of look like what you’d imagine a rising bubble of wetter air would. The ripple patterns you sometimes see in altocumulus clouds look like wave action. The elongated wispy patterns of cirrus clouds make some sense if you imagine the wind stretching out a mass of cloud. But why would there be the filaments? The guides I’ve found online just take it for granted. Similarly, the globular altocumulus structure is regarded as a matter of definition.

What’s going on in there?

Here’s video of Phidippus adumbrata jumping spiders mating.

The male has two primary concerns: he wants to mate, but he doesn’t want to get eaten. His elaborate dance is not only gauging interest, but possibly also determining his risk level in approaching the female.

Jumping spiders, in general, are very visually-oriented creatures. They have excellent vision in color. According to some studies, the arm-waving behavior is not purely visual, however, but also vibrational, and the dance differs if the male is approaching the female in her nest or out in the open.

Anyway, spoiler alert, this male succeeded in mating and avoided being eaten (at least for the time being).