|Hackled Lace Weaver Spider - Uloborus glomosus|
Family: Uloboridae - the only family of spiders
that do not have venom glands.
Spider Index | Spider Main | Orb Web | Cobweb
Fig. 1. Cribellum and calamistrum. Live adult spider with "hackled" (combed) web
Spiders in the family Uloboridae are called cribellate orb weavers. Rather than relying on sticky silk to trap prey, the Uloboridae silk entraps insects by entangling their legs. The special silk is pulled from a field of very fine set of spinneret "spigots", called the cribellum, and spun with a "back-combing" movement of a special comb on the spider's rear legs. It has been shown the process of "back-combing" imparts an electrostatic charge onto the silk, causing it to attract small objects in the vicinity (insect legs) and helps to ensnare the unfortunate prey.
This tiny spider has incorporated stabilimenta in her web. Stabilimenta are conspicuous lines or spirals of silk, included by many diurnal spiders at the center of their otherwise cryptic webs. It has been shown spider webs using stabilimenta catch, on average, 34% fewer insects than those without. However, webs with the easily-visible markings are damaged far less frequently by birds flying through the web. It is an evolutionary tradeoff the spider can influence every time it builds a new web. The inclusion of stabilimenta is influenced by many factors, including prey density and web location.
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Class Arachnida / Order Araneae: Spiders are the largest group of arachnids. They are easily recognized by their eight legs, and there are few creatures great or small that elicit such irrational fear in mankind. The vast majority of spiders are completely harmless and offer beneficial services, chief of which is keeping the burgeoning insect population in check. I am continually amazed at the resourcefulness of these supremely successful predators. Spider Index | Spider Main