Observation on silk production and morphology of silk in water mites (Acariformes: Hydrachnidia)

Abstract

Adults of the following water mite species – Piona coccinea (C.L. Koch, 1836), Limnesia undulata (O.F. Müller, 1776), Limnesia maculata (O.F. Müller, 1776), Limnesia undulatoides (Davids, 1997), Hydryphantes ruber (de Geer, 1778) and Mideopsis orbicularis (O.F. Müller, 1776) maintaining in the laboratory for several months were shown to permanently produce various amount of silk in the form of long thin unbrunched threads. Morphology of these threads are similar in all studied species – they are stright, rigid, mostly hollow tubes of two dimension categories: thin 730±130 nm, and thick 1–2.5 μm in diameter. Predominance of different thread types varies freely in different mite species. Specific staining reveals neither DNA nor microbial walls in threads composition, so the microbial origin of threads is excluded. Staining with Calcofluor White M2R fluorochrome definitely indicates that these threads belong to arthropod silk. Organization of the threads is found to be simplest among known spiders and insect’s silks. The observed silk formation does not correspond to the mite reproduction activity because has lasted from late summer till mid autumn where mites have already completed producing both eggs and spermatophores. Possible functions of the silk are discussed.