Do Spiders Contain Protein?

Spiders do not have a urinary bladder or a liver-bile system. Instead, spiders digest protein and lipids. Their dietary proteins are used for silk spinning, enzymatic digestion, and other biological processes.

The lipid:protein ratios of spiders were influenced by the nutrient compositions of their prey. High protein prey increased the body size of spiders. As a result, spiders gained more energy and consumed more food. In contrast, the protein:lipid ratio of spiders decreased when they were fed with protein rich prey. This may be due to a decreased rate of incorporation of ingested protein into the body.

A large proportion of the silk protein in spiders is a hydrophobic amino acid. It contains large amounts of nonpolar amino acids, including glycine, leucine, alanine, and proline. These nonpolar amino acids are believed to help maintain the liquid-crystalline behavior of spider silk proteins.

Spiders are opportunistic eaters, feeding on as many insects as possible in a short time. They use proteolytic enzymes extensively for digestion.

They also store insoluble wastes in a cloaca. Most spider species are not carrion feeders. However, some of them do sequester waste materials on their exoskeletons.

The faecal material of spiders is usually whitish in colour. They contain nitrogenous wastes and uric acid. While they do not eat many complex carbohydrates, some of their prey may metabolize sugars.

Some spiders have simple enzyme-secreting glands near their oral opening. However, these glands seem to be relatively unimportant.

One of the most remarkable traits of spiders is their silk. These fibers are extremely long, with flakes of protein that are five to fifteen nanometres in length. To obtain a sample, silk from a spider Nephila edulis was collected and spun. Researchers then analyzed the silk proteins using 13C magic-angle spinning nuclear magnetic resonance (MAS NMR).

Results showed that the resolved peaks for glycine and Ala tensors are largely in the range of b-sheets. Moreover, these two amino acids have similar principal values.