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November, 2010

A Thousand Words

by Valerie

Some pictures tell the whole story, while others might leave a viewer with more questions than answers. Sometimes, a picture needs an interpreter, especially if it shows unfamiliar subjects.

The three reddish winged insects in the accompanying photo are scorpionflies. They are in a small order of insects called Mecoptera, their family name is Panorpidae, and they are identified as Panorpa nuptialis. Scorpionflies get their common name from the male's unusual tail; it resembles a scorpion's stinger but has two points instead of one. In reality, scorpionflies do not bite or sting. They are completely harmless.

Here in central Texas, we have just one species of this odd insect, and adults only appear in the late autumn (this photograph was taken in November). The rest of the year, scorpionflies exist as eggs, larvae, or pupae. Both the larvae and the adults are scavengers, feeding on dead insects. While larvae live on the ground, adults are often found in and around spider webs, and they are adept at eating the prey caught in the silk. This habit is referred to as kleptoparasitism. In this photo, the web is old and the spider has departed (probably for arachnid heaven). The web belonged to a large orbweaver in the genus Argiope, which are commonly called garden spiders. The mangled mess stuck in the web is the corpse of a Broad-tipped Conehead (Neoconocephalus triops), a kind of katydid. The "conehead" is the blunt point at the bottom left. These katydids have very large jaws (one is visible at the bottom - with a dark, pointy tip at right) and can give a painful bite if handled carelessly. Obviously, though, the katydid's defenses did it no good against the spider's web and venom. Because the katydid remains are still stuck in the web, the spider was evidently removed from the web shortly after it had secured its prey. It may even have fed for awhile. However, once a garden spider is done with its meal, it neatly cuts the web around the hard inedible bits and allows the mass to drop out of the web. It's sort of like taking out the garbage. Instead, not only is the prey still in the web, but the web is ruined. No self-respecting spider would tolerate this without repairing it, so the web is obviously abandoned. A quick search of the area revealed no spider, and garden spiders cannot move very far from their web because their legs are not designed for walking. Hence, the conclusion is that the spider was probably nabbed by a bird or other predator.

Back to the scorpionflies. All insects must have some way of surviving predation. These are not particularly fast or strong flyers and their relatively large size (about 20 mm in length) makes them very obvious targets. The same hues that make them so visible are also their defense. In the arthropod world, red, yellow and black are warning colors. They signal that an insect will taste nasty if eaten, whether it is because of a poisonous diet or venom. The colors on the scorpionflies are very similar to some wasps and so that is what they are probably mimicking.

This trio consists of two females and a male. The females are both feeding on the katydid remains, using their long snouts to probe into the exoskeleton shell to find bits of edible flesh. The female on the left is mating with a male that is facing away from the camera. He is not eating, as is usual when insects mate. The females often eat while the male just does his job. With a life span of but a year, it doesn't pay to waste time.

There is one more bit of information that will help complete this photograph's story. I find scorpionflies every year, but usually I am lucky to see two or three in a season. This year, I have found more than a dozen. I've never before seen a pair mating, let alone a group of them together. Our weather during the past summer was relatively mild and we had a good amount of rain. The conditions were probably very good for the survival of scorpionfly larvae, resulting in more adults.

So now, with a bit of background information, this illustration really does encompass a bunch of words. Although it is not nearly a thousand, it is far more than "three weird looking bugs on garbage."

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