A novel property of spider silk: chemical defence against ants

Abstract

Spider webs are made of silk, the properties of which ensure remarkable efficiency at capturing prey. However, remaining on, or near, the web exposes the resident spiders to many potential predators, such as ants. Surprisingly, ants are rarely reported foraging on the webs of orb-weaving spiders, despite the formidable capacity of ants to subdue prey and repel enemies, the diversity and abundance of orb-web spiders, and the nutritional value of the web and resident spider. We explain this paradox by reporting a novel property of the silk produced by the orb-web spider Nephila antipodiana (Walckenaer). These spiders deposit on the silk a pyrrolidine alkaloid (2-pyrrolidinone) that provides protection from ant invasion. Furthermore, the ontogenetic change in the production of 2-pyrrolidinone suggests that this compound represents an adaptive response to the threat of natural enemies, rather than a simple by-product of silk synthesis: while 2-pyrrolidinone occurs on the silk threads produced by adult and large juvenile spiders, it is absent on threads produced by small juvenile spiders, whose threads are sufficiently thin to be inaccessible to ants.

Nectar Theft and Floral Ant-Repellence: A Link between Nectar Volume and Ant-Repellent Traits?

“…This repellence is most effective at close range, in a similar way to the silk of some orb-web spiders being repellent to ants only upon contact [51]. As most of the species studied produced flowers that lasted less than a day, pollen-based repellence would be sufficient to dissuade ant-recruitment to flowers throughout the most crucial period of pollinator visitation, leaving only a short period of vulnerability in protandrous species where the stigma was receptive but no further self-pollen was present.…”

Storage and release of hydrogen cyanide in a chelicerate ( Oribatula tibialis )

“…Although no cyanogenic species has been known among Chelicerata, chemical defense is widespread in the group, particularly among arachnids such as whip scorpions (16,17), harvestmen (18,19), certain spiders (20), and mites (21,22). Here, we demonstrate cyanogenesis in a mite of the order Oribatida, a diverse and mostly soil-dwelling group of decomposers that discharge myriad defenserelated semiochemicals from a pair of large exocrine opisthonotal oil glands (22)(23)(24)(25)(26)(27)(28).…”

Exploring the global animal biodiversity in the search for new drugs – Spiders, scorpions, horseshoe crabs, sea spiders, centipedes, and millipedes

“…Some of these substances may also lead to important industrial applications. For instance, many spider venoms are deadly to insects but harmless to vertebrates and may be a less polluting alternative to conventional pesticides [261], while the 2-pyrrolidinone in the silk of N. antipodiana could lead to the development of a new insect repellent for human use [45]. Notably, the relatively recent discovery of the small crustacean class Remipedia [262] that appeared to produce a unique cocktail of digestive enzymes and neurotoxins to paralyze their prey [26] hints to the existence of many more exceptional arthropod-based bioactive molecules.…”

“…The batik golden web spider Nephila antipodiana Walckenaer, 1841 (Arachnida, Araneae: Araneidae) in the tropical forests of South-east Asia incorporates 2-pyrrolidinone in the silk it uses to spin its web in order to ward off predatory ants, moths, and caterpillars [45].…”