Web Silk Research Articles

Uncoiling springs promote mechanical functionality of spider cribellate silk.

Composites, both natural and synthetic, achieve novel functionality by combining two or more constituent materials. For example, the earliest adhesive silk in spider webs - cribellate silk - is composed of stiff axial fibers and coiled fibers surrounded by hundreds of sticky cribellate nanofibrils. Yet, little is known of how fiber types interact to enable capture of insect prey with cribellate silk. To understand the roles of each constituent fiber during prey capture, we compared the tensile performance of native-state and manipulated threads produced by the cribellate spider Psechrus clavis, and the adhesion of native threads along a smooth surface and hairy bee thorax. We found that the coiled fiber increases the work to fracture of the entire cribellate thread by up to 20-fold. We also found that the axial fiber breaks multiple times during deformation, an unexpected observation that indicates: (i) the axial fiber continues to contribute work even after breakage, and (ii) the cribellate nanofibrils may perform a previously unidentified role as a binder material that distributes forces throughout the thread. Work of adhesion increased on surfaces with more surface structures (hairy bee thorax) corresponding to increased deformation of the coiled fiber. Together, our observations highlight how the synergistic interactions among the constituents of this natural composite adhesive enhance functionality. These highly extensible threads may serve to expose additional cribellate nanofibrils to form attachment points with prey substrata while also immobilizing prey as they sink into the web due to gravity.

Female false black widow spiders,Steatoda grossa,recognize webs based on physical and chemical cues

AbstractFemales of the false black widow,Steatoda grossaCL Koch (Araneae: Theridiidae), invest significant energy and time weaving cobwebs. We tested the hypothesis thatS. grossafemales select sites for their webs based, in part, on the presence of con‐ or heterospecific webs, sensing both physical and chemical web cues. In bioassays, we offered femaleS. grossaa choice between an empty control frame and a frame bearing the web of a conspecific female or that of a female common house spider,Parasteatoda tepidariumCL Koch (Araneae: Theridiidae), recording (1) the time she spent, and (2) the time she spent inactive (a proxy for settling behaviour) on each frame. We also tested the effect of (1) silk micro‐ and macrostructure (wrapped‐up silk or intact web, each semiochemical‐deprived), (2) plastic webs, and (3) silk semiochemical extract on the responses ofS. grossafemales. Females settled on both con‐ and heterospecific webs and chose test stimuli based on their chemical and physical characteristics. Even plastic webs in cobweb‐like arrangement readily prompted settling behaviour by females. Our results suggest that web architecture, rather than web silk, mediates settling responses by femaleS. grossaon pre‐existing webs which may provide structural support for a new web and indicate habitat suitability.

Functional trade-offs in cribellate silk mediated by spinning behavior

Web-building spiders are an extremely diverse predatory group due to their use of physiologically differentiated silk types in webs. Major shifts in silk functional properties are classically attributed to innovations in silk genes and protein expression. Here, we disentangle the effects of spinning behavior on silk performance of the earliest types of capture threads in spider webs for the first time. Progradungula otwayensis produces two variations of cribellate silk in webs: ladder lines are stereotypically combed with the calamistrum while supporting rail lines contain silk that is naturally uncombed, spun without the intervention of the legs. Combed cribellate silk is highly extensible and adhesive suggesting that the reserve warp and cribellate fibrils brings them into tension only near or after the underlying axial fibers are broken. In contrast, these three fiber components are largely aligned in the uncombed threads and deform as a single composite unit that is 5–10x stronger, but significantly less adhesive, allowing them to act as structural elements in the web. Our study reveals that cribellate silk can occupy a surprisingly diverse performance space, accessible through simple changes in spider behavior, which may have facilitated the impressive diversification of web architectures utilizing this ancient silk.

Evaluation of a Lignin-Encapsulated Nootkatone Formulation AgainstTetranychus urticae(Acari: Tetranychidae)

Botanical-based miticides, such as neem oil, are used in organic and conventional agronomic production as part of chemical rotation plans to suppress pest mite populations. Other plant-based compounds such as nootkatone (a component of essential oils distilled from grapefruit, Citrus paradisi Macfayden (Rutaceae), and Alaskan yellow cedar, Chamaecyparis nootkatensis [D. Don] Spach [Cupressaceae]), also may serve as effective organic miticides in crop production systems. We report on a lignin-encapsulated (LE) nootkatone formulation (previously effective at repelling ticks) that was evaluated as a miticide against the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). At an application rate of 1 g/L AI, LE nootkatone caused 85% mortality of spider mites in the absence of silk webbing, but only 12% mortality when webbing was present. Another component of Alaskan yellow cedar oil, carvacrol, was added at a rate of 1 ml/L to the LE formulation. Spider mite mortality to this formulation, with webbing present, increased to 81%. Although the LE nootkatone and carvacrol combination exhibited phytotoxicity, it does have potential as a miticide. However, more work is needed to reduce the phytotoxicity of current formulations.

Effect of Sericin Content on the Structural Characteristics and Properties of Electro-spun Regenerated Silk

Electro-spun silk web has attracted attention for biomedical applications because of its excellent bio-compatibility and facile fabrication method. Because biomedical applications require various performances of silk web, many studies have been conducted on the effect of the variables associated with their preparation on the structure and properties of silk web. In the present study, the effect of residual sericin content on the morphology, structural characteristics, and properties of electrospun regenerated silk web was examined. The regenerated silk without sericin (i.e., silk with 100 wt% fibroin) did not show good electro-spinnability. However, the electro-spinnability improved remarkably above a sericin content of 0.6 wt%. The crystallinity index of the electro-spun silk increased at 0.6 wt% sericin content and decreased above 8.2 wt% sericin. The mechanical properties of the electro-spun silk webs showed a similar trend as their crystallinity indices. The breaking strength and elongation improved significantly at 0.6 wt% sericin content and both parameters gradually decreased above this value. The thermal stability of the silk web decreased slightly upon increasing the sericin content.

Shelter Building and Extrafloral Nectar Exploitation by a Member of theAristotelia corallinaSpecies Complex (Gelechiidae) on Costa Rican Acacias

A new member of the unresolved Aristotelia corallina Walsingham species complex (Gelechiidae) from a Costa Rican dry forest (Parque Nacional Palo Verde) is reported. Its larval behavior and possible relationships to the rest of the complex are described and analyzed. Field and laboratory observations revealed that these caterpillars consumed the extrafloral nectar, Beltian bodies, and young foliage of two acacia species (Vachellia collinsii and Vachellia farnesiana; Fabaceae: Mimosoideae). The caterpillars were observed building individual silk webs surrounding a single stem node's thorns and leaf rachises. If open domatia are included in shelters, the caterpillars reside in the domatia between feeding bouts and during pupation. These caterpillars are the only non-myrmecophilous caterpillars known to regularly exploit a host plant's ant rewards. DNA barcoding of the Costa Rican specimens showed that they are significantly different from the United States members of A. corallina (12–13% difference in cox1 sequence). An examination of host plant herbarium material for caterpillar shelters demonstrated likely differences in host plant use, with webs consistent with A. corallina only found on specimens of United States Chamaecrista nictitans (Fabaceae: Caesalpiniodeae), but not Vachellia farnesiana. By contrast, webs were found on V. collinsii, V. cornigera, and V. farnesiana from Central America (including Mexico), but not on Central American C. nictitans. This ecological evidence suggests that the Costa Rican populations of A. corallina may be more closely related to the Mexican populations than to the US populations.

Reproductive aspects of the Purple-throated Euphonia, Euphonia chlorotica (Aves: Fringillidae) in southeastern Brazil, and first record of the species nesting inside a vespiary

Despite the fact thatE. chlorotica(Linnaeus, 1766) is common and widely distributed in South America, the reproductive aspects of the species are poorly documented. Here we present data on 18 active nests found from August to February, between 2007 and 2012. Nests were globular with a lateral entrance, and measured 97.9 ± 14.4 mm in outside height, 110.6 ± 11.6 mm in outside diameter, and were 4.88 ± 2.09 m above ground. They were often supported from bellow and were composed mainly of tiny dry leafs and leaflets, fine petioles, and plumed seeds, all compacted with spider web silk. Eggs were laid on consecutive days or with one day interval, and clutch size varied from 1–3 eggs (2.1 ± 0.6, n = 9 nests). Only females incubated the eggs, but both sexes were involved in nest construction and nestling attendance at similar rates. Incubation and nestling periods were 14 and 21 days, respectively, and overall nest survival probability was 5%. A vespiary used for nesting was not occupied by wasps and nest material was deposited only to form the incubatory chamber. Although nesting near wasps or bees is a widespread strategy among birds in general, nesting inside the nests of social insects is a poorly documented behavior.

Preparation of new natural silk non-woven fabrics by using adhesion characteristics of sericin and their characterization

Electro-spun regenerated silk webs have been extensively studied for biomedical applications because of the simplicity of their fabrication methods However, the productivity of the electro-spinning process is low for web fabrication and the mechanical properties of the electro-spun silk web are not satisfactory, which restricts its commercialization. In this study, a new silk non-woven fabric was successfully fabricated by wetting and hot press treatments using the excellent binding characteristic of sericin. The effects of the press temperature and residual sericin content on the preparation, structure, and properties of the silk non-woven fabric were examined. A press temperature of 200°C was optimum for obtaining non-woven fabrics with best mechanical properties, without yellowing. The silk non-woven fabric could not be fabricated without sericin, and a minimum of 8% sericin was required to fabricate it. As the sericin content was increased, the strength and Young’s modulus of the silk non-woven fabric increased, while the tensile elongation remained constant. Regardless of the press temperature and sericin content, all the silk non-woven fabrics showed good cell viability, comparable to that of the tissue culture plate (TCP) used as a control until 4days, which however decreased compared to that of TCP after 7days.

Punctuated evolution of viscid silk in spider orb webs supported by mechanical behavior of wet cribellate silk.

The origin of viscid capture silk in orb webs, from cribellate silk-spinning ancestors, is a key innovation correlated with significant diversification of web-building spiders. Ancestral cribellate silk consists of dry nanofibrils surrounding a stiff, axial fiber that adheres to prey through van der Waals interactions, capillary forces, and physical entanglement. In contrast, viscid silk uses chemically adhesive aqueous glue coated onto a highly compliant and extensible flagelliform core silk. The extensibility of the flagelliform fiber accounts for half of the total work of adhesion for viscid silk and is enabled by water in the aqueous coating. Recent cDNA libraries revealed the expression of flagelliform silk proteins in cribellate orb-weaving spiders. We hypothesized that the presence of flagelliform proteins in cribellate silk could have allowed for a gradual shift in mechanical performance of cribellate axial silk, whose effect was masked by the dry nature of its adhesive. We measured supercontraction and mechanical performance of cribellate axial silk, in wet and dry states, for two species of cribellate orb web-weaving spiders to see if water enabled flagelliform silk-like performance. We found that compliance and extensibility of wet cribellate silk increased compared to dry state as expected. However, when compared to other silk types, the response to water was more similar to other web silks, like major and minor ampullate silk, than to viscid silk. These findings support the punctuated evolution of viscid silk mechanical performance.

A trap and a lure: dual function of a nocturnal animal construction

Animals that use deceptive visual signals to attract prey often employ colour mimicry or bioluminescence but less commonly self-excreted lures. The conspicuous web decorations and silks of some web-building spiders have been shown to visually lure prey in the daytime. However, it remains unknown whether spider webs can also lure prey at night with these self-produced silks. In this study, we tested this hypothesis by manipulating the coloration of the webs of Psechrus clavis and the presence of the web dwellers. We monitored the foraging performance of four treatment groups (spider present, normal web; spider present, blackened web; spider absent, normal web; spider absent, blackened web) and measured the reflectance spectra of spider body parts and web silks. We found that both spider body colour and web silk can lure insect prey at night. Lepidopteran insects comprised the majority of attracted prey. This study is the first to empirically demonstrate that animals can use self-produced substances to visually lure prey in a nocturnal environment and improve foraging success.

The potential role of web-based putrescine as a prey-attracting allomone

The use of prey-attracting allomones is likely to be an effective foraging strategy for sit-and-wait predators. Despite this, the production and efficacy of such allomones have rarely been documented. Previous investigations into the chemical composition of spider silk have revealed the presence of a number of potential allomone chemicals such as the amide putrescine, a foul-smelling organic compound. Putrescine is attractive to several terrestrial invertebrates, many of which are also typical prey species of spiders, but whether prey attraction is an underlying mechanism promoting its inclusion in web silk is currently untested. Here, we artificially increased the amount of putrescine in the web silk of female Argiope keyserlingi and assessed the resulting variation in prey interception of normal versus putrescine augmented webs under seminatural field conditions. We demonstrated that webs misted with a putrescine solution captured significantly more prey than webs misted with a control solution and also found differences in prey capture rates between individuals from different populations. This not only suggests that web-bound putrescine acts as a prey attracting allomone, but also that there is population level variation in the web-based foraging strategies of these spiders.

Locking out predators by silk, a new counterattack behaviour in a social spider mite

1. A type of arms race that includes predation, counterattacks and cross‐counterattacks occurs between the phytophagous mite Stigmaeopsis nanjingensis (Ma et Yuan), which lives in self‐woven nests and exhibits cooperative sociality, and its specialised phytoseiid mite predator, Typhlodromus bambusae Ehara.2. First, the efficiency of the S. nanjingensis (prey) counterattacking T. bambusae (predator) was observed. The prey females frequently locked the immature predators out of their nests using silk web, and the predators subsequently died of starvation. Furthermore, the prey males often killed immature T. bambusae mites after they invaded the nests.3. This reversal of roles in the predator–prey system was then re‐reversed (returned to a normal state) by the behaviour of T. bambusae females. Immature predators could maintain their predacious natures due to the presence of attending adult females, which are able to cope with the prey counterattack behaviours.

Adaptive advantages of appearance: predation, thermoregulation, and color of webbing built by New Zealand's largest moth.

Prey are often difficult to locate visually, which may help them avoid predators. However, an animal's appearance might also evolve in response to the abiotic environment. Here, we investigate the processes that determine the appearance of silk webbing built by New Zealand's largest endemic moth Aenetus virescens (Lepidoptera: Hepialidae), whose larvae burrow into the trunks of native trees. Larvae cover tunnel entrances with silk webbing, detritus, and epiphytes, giving them a similar appearance to tree bark. First, we conducted spectral analyses of webbing and background bark in avian tetrahedral color space to test whether webbing made larvae less visible to predatory parrots. Next, we manipulated the spectral contrast of webbing and background bark and assessed its effect on predation by parrots for over 2yr. Last, we measured the effect of webbing on tunnel temperatures and quantified how temperatures within tunnels affected larval growth. Results indicate that webbing made larvae less visible to predatory parrots. However, webbing contrast to background bark did not affect predation by parrots. Instead, webbing increased temperatures within tunnels and facilitated more rapid larval growth. Overall results indicate that the appearance of organisms that are difficult to locate visually may not always result from selection by predators.

Synthesis of a Carbon-activated Microfiber from Spider Webs Silk

Carbon fiber of spider web silk has been produced through the simple carbonization process. Cobwebs are a source of strong natural fiber, flexible and micrometer in size. Preparation of micro carbon fiber from spider webs that consist of carbonization and activation processes. Carbonization was performed in N2 gas environment by multi step heating profile up to temperature of 400 °C, while the activation process was done by using chemical activation with KOH activating agent assistance. Measurement of physical properties was conducted on the surface morphology, element content and the degree of crystallinity. The measurement results found that micro carbon fiber from spider webs has a diameter in the range of 0.5 -25 micrometers. It is found that the carbon-activated microfiber takes the amorphous form with the carbon content of 84 %.

Unearthing ecological wisdom from natural habitats and its ramifications on development of biocement and sustainable cities

As the world population migrates to the urban areas in increasingly greater numbers, building and maintaining urban infrastructure in a sustainable fashion is a great challenge. Present construction technologies use too much material and energy and produces huge quantities of greenhouse gases. Nature, on the other hand, has been building habitats such as ant hills, coral reefs and silk webs that has been sheltering billions of species for millions of years in a sustainable way. The ecological wisdom embodied in these high-performance prototypes may give us clues to sustainable urban infrastructure. In this paper we highlight some of the amazing ecologically wise natural habitats. Although many amazing natural examples have been recently highlighted, emulating them in engineering practice has remained a challenge. One of the most promising biological processes that are closest to human adaptation is biomineralisation by which living organisms produce minerals, chiefly carbonate products that offer strength to bones, shells and antlers. With the help of some microorganisms, it is possible to produce and deposit minerals (e.g. calcium carbonate) and emulate some of the biological processes such as formation of corals. This paper briefly discusses biomineralisation technology. The present status of application of the technology in urban infrastructure has been summarised.

Silkomics: Insight into the Silk Spinning Process of Spiders.

The proteins from the silk-producing glands were identified using both a bottom-up gel-based proteomic approach as well as from a shotgun proteomic approach. Additionally, the relationship between the functions of identified proteins and the spinning process was studied. A total of 125 proteins were identified in the major ampullate, 101 in the flagelliform, 77 in the aggregate, 75 in the tubuliform, 68 in the minor ampullate, and 23 in aciniform glands. On the basis of the functional classification using Gene Ontology, these proteins were organized into seven different groups according to their general function: (i) web silk proteins-spidroins, (ii) proteins related to the folding/conformation of spidroins, (iii) proteins that protect silk proteins from oxidative stress, (iv) proteins involved in fibrillar preservation of silks in the web, (v) proteins related to ion transport into and out of the glands during silk fiber spinning, (vi) proteins involved in prey capture and pre-digestion, and (vii) housekeeping proteins from all of the glands. Thus, a general mechanism of action for the identified proteins in the silk-producing glands from the Nephila clavipes spider was proposed; the current results also indicate that the webs play an active role in prey capture.

Prey capture by the purse-web spider <I>Calommata signata</I> (Araneae: Atypidae)

Prey capture and subsequent behaviors of Calommata signata (Araneae: Atypidae) were observed and video-documented in the laboratory Our observations indicated that the spider captures various soil animals by using only its chelicerae. Furthermore, when closing the entrance of the burrow, the spider made a provisional cover of the entrance by hooking and drawing the inner surface of the burrow before covering the entrance with silk webbing from its spinnerets.

Confronting Religious Extremism in the New Silk Web

The rise in religious extremism is highly documented, but not well understood. The most frequently cited explanations are economic and sociological. However, the specific role of religion has recei...

Bio-inspired networks for optoelectronic applications.

Modern optoelectronics needs development of new materials characterized not only by high optical transparency and electrical conductivity, but also by mechanical strength, and flexibility. Recent advances employ grids of metallic micro- and nanowires, but the overall performance of the resulting material composites remains unsatisfactory. In this work, we propose a new strategy: application of natural scaffoldings perfected by evolution. In this context, we study two bio-inspired networks for two specific optoelectronic applications. The first network, intended for solar cells, light sources and similar devices, has a quasi-fractal structure and is derived directly from a chemically extracted leaf venation system. The second network is intended for touch screens and flexible displays, and is obtained by metalizing a spider's silk web. We demonstrate that each of these networks attain an exceptional optoelectonic and mechanical performance for its intended purpose, providing a promising direction in the development of more efficient optoelectronic devices.

Role of silk webbing in the biology of Hemicheyletia wellsina (Acari: Cheyletidae)

Hemicheyletia wellsina is a predator of several families of arthropod plant pests. Hemicheyletia wellsina females produce silk webbing that covers their egg clutches, but the function of the webbing is unknown. Experiments indicate the webbing can protect the eggs from predation, resulting in approximately a 71% increase in egg hatch compared to when silk was removed in the presence of the phytoseiid predator Metaseiulus occidentalis. Within 2–3 days after larvae hatch, they appear to no longer need protection, as 18 of 20 H. wellsina larvae captured and fed on the much larger adult M. occidentalis females. The silk also may regulate the relative humidity around the eggs.