Humidity‐dependent mechanical and adhesive properties of Arachnocampa tasmaniensis capture threads. (4th May 2018)

• Record Type: Journal Article
• Authors: Piorkowski, D.; Blackledge, T. A.; Liao, C.‐P.; Doran, N. E.; Wu, C.‐L.; Blamires, S. J.; Tso, I.‐M.
• Is Part Of: Journal of zoology. Volume 305:Number 4(2018)
• Page Start: 256
• Page End: 266
• Publication Date: 2018-05-04
• Subjects: glow‐worm -- Arachnocampa -- silk -- adhesion -- biomaterial -- prey capture -- biomechanics; Zoology -- Periodicals; Zoologie -- Périodiques; 590.5
• DOI: 10.1111/jzo.12562
• Languages: English
• ISSNs: 0952-8369

Abstract

Abstract: Bioluminescent glow‐worms ( Arachnocampa spp.) capture prey in glue‐coated silk capture threads hung from their nests on damp cave and wet forest substrates. In a dry environment, these animals are very susceptible to desiccation as their bodies can become life threateningly dry and their silk has been anecdotally observed to become non‐sticky. Water has a plasticizing effect on the structural proteins of several invertebrate silks, including those used in caddisfly nets, mussel byssus and spider webs. Moreover, water facilitates interfacial adhesion by spreading adhesive biomolecules in functionally analogous velvet worm slime and spider silk glue. We tested the effects of water on the mechanics and adhesion of Arachnocampa tasmaniensis capture threads sampled within damp caves. We found that threads tested at high humidity were three times more compliant and over 10‐fold more extensible than those tested at low humidity (30% RH). We also found the threads to be significantly more adhesive in high humidity with force at detachment increasing two orders of magnitude and work of adhesion increasing by five orders of magnitude compared to threads tested at low humidity. Our results unequivocally demonstrate that A. tasmaniensis capture thread functionality is dependent upon exposure to high humidity. Our results both confirm previous reports and indicate that the foraging habitat of these animals is restricted to caves and cave‐like environments, such as wet forests. Abstract : Bioluminescent glow‐worms catch prey using glue‐coated capture silk threads hung vertically from their nests on damp cave and wet forest substrates. We found that threads tensile and adhesion tested at >90% RH (relative humidity) were three times more compliant and over 10‐fold more extensible with work of adhesion increasing by five orders of magnitude compared to threads tested at 30% RH, which were relatively brittle and non‐adhesive. Our results unequivocally demonstrate that A. tasmaniensis capture thread functionality is dependent upon exposure to high humidity which likely indicates that these animals' foraging habitat is restricted to environments with sufficiently high humidity.