Entomologists have an overall appreciation of insects. I, on the other hand, am much more selective.
I love butterflies, ladybugs and honeybees. I can relate to fireflies and grasshoppers. However, I cannot work up any enthusiasm for spiders, although the beauty of their webs is incomparable.
Years ago I had already noticed that large webs seemed to proliferate as the weather turned colder. I would check the webs every morning and they seemed to become bigger each day. The spider, staring at me with its glistening black eyes, seemed to become bigger as well.
Having found a mentor for all things insectoidal at the state Department of Environmental Conservation, I sought information. “Oh,” said the person I was talking to, “you mean pumpkin spiders!” Or, more scientifically, Araneus diadematus.
It is unclear where that nickname originated, but there are two theories. The first suggests that it is a reference to its plump abdomen. The second, they are common around Halloween time.
The more common nickname, however, is (garden) cross spider because running down the midline of the top of the abdomen (dorsal surface) is a folium — a marking that suggests a leaf. This spider has yellow or white spots around the folium in such a way that it forms a design reminiscent of a cross.
While spiders and insects are both classified as arthropods, they are members of different subphyla and are not closely related. Spiders are members of subphylum chelicerata, and insects occupy the subphylum hexapoda. There are many anatomical differences between them, the most obvious being that spiders have only two main body parts — a head, called the “cephalothorax,” and an abdomen, called the “opisthosoma.”
Insects have three body segments: the head, the thorax and the abdomen. Insects have three pairs of legs, and spiders have four. Spiders do not have antennae.
The subphylum name chelicerata refers to the mouthparts, or “jaws,” which can be hollow and can inject venom into prey. Araneus is from the Latin for “spider,” and diadematus refers to the markings, which apparently, some see as crown-shaped.
Spider ancestors appeared in the Devonian period (between 419 and 358 million years ago), while true spiders made their appearance in the later Carboniferous, approximately 300 million years ago.
The oldest spider web together with its prey — a now-extinct parasitic wasp Hymenoptera evaniidae — was found in an amber specimen from 110 million years ago in Spain. Before that find, the oldest evidence for spider silk was a single, 4mm strand from a Lebanese amber sample from 130 million years ago. The Spanish specimen contained five strands from a more complex structure resembling a modern orb web.
There are several web types, although web structure is not considered a diagnostic element in assigning spiders to their various families. The vertical orb web may be the most familiar, although some species build horizontal orb webs.
Sitting in our sukkah we watched a small spider attempt to build a web across a ceiling decoration. That important first strand is adhesive and floats on an air current to a second anchor point. When it attaches to a support, the spider will run across it several times, strengthening it with the addition of more threads.
The next attachment will make a Y-shaped unit with each strand called a radial. Further radials will then be added. After all the radials are in place, the spider returns to the center and strengthens the area with five circular threads.
Moving outward, the spider then continues making a spiral from center to hub (perimeter of web) of non-adhesive threads.
Once that is complete, the spider will replace those threads with more closely placed adhesive ones.
Because the center of the web is exposed to predators, the spider will usually move to the hub, but place a signal line on the web so that it can feel vibrations when an insect becomes stuck to the web. A spider avoids being stuck in its own glue through careful movement, dense hairs on the legs that reduce the area of contact with the glue, and a non-stick material on their feet.
Less familiar web types include funnel webs, tubular webs and sheet webs. Our common cobwebs start out as spider webs, particularly from family Theridiidae, that become covered in dust and then are abandoned.
Spiders are not the only animals that produce silk. While we are familiar with silkworms and the silk produced from their unraveled cocoons, many other insects produce silk. These include weaver ants Oecopylla that use silk to make communal nests, and honeybee and bumblebee larvae that make silk to strengthen the wax cells in which they pupate.
However, these animals make only one type of silk while spiders make a total of seven — three in males and four in females.
More next time!
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