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Showing posts from 2014

Difficulty identifying Anyphaena dixiana

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Usually when I come across a spider, I can tell which family of spiders it belongs to, but this spider baffled me. I found a female under a dog bed on my patio on November 23, 2014, in Austin Texas. Three days later I found a similar-looking male spider, and again I couldn't be sure of the family.


The female is on the left, the male on the right. These photos are not proportionally scaled: the female has a body length of 4.5mm and the male 4mm. We don't include the legs.

These two spiders have the general body shape and color pattern of a wolf spider (lycosidae), but they don't have the eyes of a wolf spider. Often a spider that looks like a wolf spider but isn't might be a funnel spider (agelenidae), but these eyes also were not a match for agelenidae. It is hard to see in these photos, but these spiders' eyes are in two rows of four, with all eyes about the same size. Funnel spiders have eyes in three rows, except for Tegenaria, which these definitely are not.

The…

Problem-Solving Strategies

Here is a list of problem-solving strategies. Most of these strategies arose from reflection on how I develop software design specifications. This is an evolving document.

Identify and attack tangentially related problems. This often sheds light on or even resolves the original problem, even if the process happens to reveal more problems.Create solutions gradually by iterative refinement. The best solutions are evolved. Solve select problems, leaving others unsolved. Gradually throw more solutions into the mix. Don't expect solutions to grow by accrual, as periodic complete transformations may be necessary. Each new iteration still benefits by being derived from preceding solutions.Find and depict specific examples of the problem. Articulate the problem separately for each example to find a common articulation or to learn the problem's component pieces.Find the right questions to ask -- about the nature of the problem and what is desired in the solution. Asking questions about …

The True King of the Sky

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The robber fly is usually considered to be the top aerial predator of the bug world. These photos may dethrone the robber fly and establish the spider as true king of the sky.

This past summer, I visited an Argiope aurantia (aka "Black and Yellow Garden Spider") in my front yard day after day to see what she was up to. She had made her web below some cables that string to my house. I often saw a robber fly monitor the sky from the bottom cable. I thought it was a cool sight and took this photo on August 7th, 2014.


Three days later, on August 10th, I found that my spider had caught a robber fly. This isn't a great photo, but it shows the spider's web near the cables on which the robber fly would perch. She is feeding on a robber fly in this photo.


This close up makes it clear that her prey is a robber fly. Out of curiosity, I kept looking for a robber fly on the cable for days afterward but never saw one there again. I suspect that my first photo is of the very robber…

Argiope aurantia under my eaves

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A new perspective of an old friend, Argiope aurantia. I have also reposted an egg sac that the spider made earlier in the summer because it fits the theme. She's variously in a bush or under my eaves.





Black silk of an Argiope aurantia

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Here are increasingly close photos of an Argiope aurantia egg sac. This is the orbweaver known as the Black and Yellow Garden Spider. The egg sac is 18mm wide (3/4") and contains 400 to 1000 eggs (Levi 1968). The first close up spans 15mm of the surface of the egg sac, the second spans 10mm, and the third spans 3mm. The spider is quite a sculptor and abstract artist.

Notice the threads of black silk. They are visible to the naked eye and appear to be on all Argiope aurantia egg sacs. I've seen them on the half dozen or so egg sacs that I've examined closely. I have not been able to determine what makes them black. It is not dirt or fungus, as they are found on new egg sacs. Brunetta & Craig 2012 reports that Nephila spiders create yellow silk with the addition of chemicals, so it's possible that Argiope aurantia is doing the same for black silk.






Argiope trifasciata hatchlings

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These are hatchlings of an Argiope trifasciata. Each has a body length of 1 mm. Body length includes the head and abdomen but not the legs. The females will grow to be up to 26 mm long.



The first photo is from her first egg sac, which numbered at least 500 spiderlings. According to the literature on this spider, up to 1000 spiderlings can emerge from a single egg sac. The second photo is from her second egg sac, which numbered only a few hundred individuals. In trying to figure out why the spiders are sometimes orange, sometimes yellow, it appears to me that they are yellow in bright light, such as direct sun or a close flash, and orange in the shade or dim light.

Argiope trifasciata is reported to overwinter in the egg sac, so these hatchlings must attempt to make it to adulthood and make egg sacs by Winter. Adult females can be found as late as December. This is the second brood of this spider, as each egg sac hatched after only a month.

Egg sac of an Argiope aurantia

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This is an egg sac of an Argiope aurantia orbweaver. It's about 2 cm (3/4") in diameter. The array of threads surrounding the egg sac help to protect it from predators and parasites.


Theridion llano, a Texas Native

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These appear to be the first photos of the tiny cobweb weaver Theridion llano, a Texas native. The spider has a body length of 1.5mm. It crawled out of a dried monarda seed head.




I owe thanks to Laura P. and Chad Heins on BugGuide for helping me to identify this, as well as to Allen Dean for confirming the identification. Here is the BugGuide entry for this spider.