ON THE PROBLEM OF THE STABILIMENTA IN SPI DER WEBS

The stabilimenta in the orb webs of Argiope bruennichi and Argiope lob ata (Araneidae) and of Uloborus walckenaerius and Uloborus plumipes (U loboridae) consist of secretions of the aciniform glands (Araneidae) a nd of these secretions together with those of the piriform glands (Ulo boridae). The same secretions are used for enveloping prey. The hypoth esis is proposed that stabilimentum building regulates the silk produc tion of these glands: silk not used for prey capture is thought to be invested into stabilimenta. Correspondingly, the expression of the sta bilimenta can vary within wide limits. This interpretation does not ex clude that stabilimenta can become useful for spiders in quite differe nt regards. This happens if stabilimentum building coincides with envi ronmental conditions under which stabilimenta are advantageous to the respective spiders in one or another respect.