Predator Perception of Detritus and Eggsac Decorations Spun by Orb-Web Spiders Cyclosa Octotuberculata: Do They Function to Camouflage the Spiders?

Current Zoology 56 (3): 379−387, 2010

Predator perception of detritus and eggsac decorations spun by orb-web spiders Cyclosa octotuberculata: Do they function to camouflage the spiders?

Wenjin GAN 1, Fengxiang LIU 1, Zengtao ZHANG 1, Daiqin LI 1, 2*

1 College of Life Sciences, Hubei University, Hubei, Wuhan 430062, China 2 Department of Biological Sciences, National University of Singapore, Singapore 117543

Abstract Camouflage is one of the most widespread and powerful strategies that animals use to make detection/recognition more difficult. Many orb-web spiders of the genus Cyclosa add prey remains, plant debris, moults, and/or eggsacs to their webs called web decorations. Web decorations resembling spider body colour pattern have been considered to camouflage the spider from predators. While this camouflage is obvious from a human’s perspective, it has rarely been investigated from a predator’s perspective. In this study, we tested the visibility of web decorations by calculating chromatic and achromatic contrasts of detritus and eggsac decorations built by Cyclosa octotuberculata, against four different backgrounds viewed by both bird (e.g., blue tits) and hymenopteran (e.g. wasps) predators. We showed that both juvenile and adult spiders on webs with detritus or egg-sac decorations were undetectable by both hymenopteran and bird predators over short and long distances. Our results thus suggest that decorating webs with detritus or eggsacs by C. octotuberculata may camouflage the spiders from both hymenopteran and bird predators in their common habitats [Current Zoology 56 (3): 379–387, 2010]. Key words Spider, Web decorations, Cyclosa octotuberculata, Camouflage, Chromatic contrast, Achromatic contrast

Most animals are under predation pressure from largely untested from a predator’s perspectives. visually hunting predators, and they have evolved a Many orb-web spiders add a variety of materials such suite of protective strategies, including camouflage, as silk ribbons, silk tufts, prey remains, eggsacs and warning signals and mimicry (Poulton, 1890; Cott, 1940; plant debris to their webs, called ‘web decorations’ Edmunds, 1974; Ruxton et al., 2004). Camouflage is a (Herberstein et al., 2000; Starks, 2002; Bruce, 2006). classical example of evolution; Darwin and Wallace However, in spite of considerable interest, widespread used it to illustrate and defend their ideas of natural se- occurrence, and being subjected to extensive research, lection (Stevens and Merilaita, 2009). It can be achieved there has been no consensus on the function of these via physical appearance (e.g. colour patterns or protec- intriguing decorations (reviewed in Herberstein et al., tive coloration), which prevents animals from being 2000; Starks, 2002; Bruce, 2006; Théry and Casas, detected and/or recognised (Stevens, 2007; Stevens and 2009). Nevertheless, web decorations are commonly Merilaita, 2009). However, while camouflage is well considered as deceptive visual signals. However, there accepted, it has only recently received significant atten- is controversy surrounding the questions of who is the tion and empirical investigations, partly because of a receiver, prey, predator or both, and whether the re- growing body of research into mimicry and warning ceiver can detect these signals (Craig and Bernard, 1990; coloration, and also increased knowledge of visual per- Blackledge and Wenzel, 2000; Bruce et al., 2005; Chou ception (Stevens and Merilaita, 2009). More importantly, et al., 2005; Cheng and Tso, 2007; Tan and Li, 2009; there has long been a common flaw in research on Tan et al., 2010). camouflage: that it is often erroneously regarded as in- Unlike Argiope spiders that decorate their webs with tuitively obvious because human perception has often only silk (Herberstein et al., 2000; Bruce, 2006), many been used to subjectively evaluate its effectiveness. orb-web spiders of the genus Cyclosa (Araneae: Ara- Thus some forms of camouflage, e.g., detritus and egg- neidae) often add prey remains, moults, plant debris or sac decorations added by orb-web spiders, remain egg sacs to their webs and place such detritus and/or

Received Nov. 17, 2009; accepted Mar. 08, 2010 ∗ Corresponding author. E-mail: [email protected] © 2010 Current Zoology 380 Current Zoology Vol. 56 No. 3 eggsacs in a vertical row of material above and below tions from spiders from a predator’s perception. the hub where the spider sits. Body size and body colo- 1 Materials and Methods ration often matches that of detritus and eggsac decorations (Marson, 1947; Rovner, 1976; Neet, 1990). It has 1.1 Study species and specimen collection long been speculated that detritus and eggsac decora- Cyclosa octotuberculata (Fig. 1A) is diurnal species tions are built to camouflage the spider against predators that spins vertical orb webs (Fig. 1B) at sunrise and (e.g., Marson, 1947; Marples, 1969; Eberhard, 1973, consumes spirals and most radial threads during the 2003, 2006; Rovner, 1976; Horton, 1980; Edmunds, following night (Tanikawa, 1992; Nakata and Ushimara, 1986; Neet, 1990), and a few observations suggest such 2004). In nature, both juveniles and adult females are camouflage properties. Eberhard (2003) observed the found to add prey remains, plant detritus (e.g., leaf component of detritus and eggsac decorations by Allo- fragments, flower pedals or small stems) and sometimes cyclosa bifurca and C. monteverde of different life moults to their webs (Fig. 1C, D). When reaching ma- stages, and found that the way the eggsacs were turity and after mating, females incorporate subse- wrapped by silk resembled the appearance of the spi- quently laid egg sacs into a string of pellets (Fig. 1E). der’s abdomen, and concluded that the decoration of A. Since spiders build their webs and decorations in wood- bifurca might function as a camouflaging device. Using lands and shrubs (W.J. Gan, personal observations), artificial webs and clay model spiders with detritus potential predators may view them against different decorations of two species of Cyclosa (C. morettes and backgrounds, e.g., green foliage, dry leaves, bark or a C. fililineata), Gonzaga and Vasconcellos-Neto (2005) blend of these three backgrounds. found that clay model spiders on detritus-decorated We collected C. octotuberculata spiders and their webs had fewer bite marks than those without, thus ar- decorations between 09:00 h and 17:00 h from April guing against the prey-attraction hypothesis and suggest 2007 to October 2008 at two study sites, Huazhong Ag- that decorating webs with detritus may reduce predation ricultural University Campus (HZAU) (30°28′48.75″N, by changing the outline image of the spiders by disrup- 114°21′03.46″E, 57 m a.s.l.), and Mt. Mo or Millstone tive coloration. A similar result was also reported in C. Hill (30°33′11.91″N, 114°24′38.14″E, 92 m a.s.l.) in octotuberculata by Baba (2003), who argued against the Wuhan, Hubei Province, China. Both juvenile and prey-attraction hypothesis, suggesting that decorating adult female C. octotuberculata as well as their decora- webs with detritus might actually reduce the predation tions were collected. For measuring reflectance spectra risk. A few recent studies indicate that predators cannot of vegetation backgrounds, we collected ten pieces of distinguish the colour signal of nonsilk decorations from green leaves for each of six plant species (Acer buer- that of Cyclosa spiders over a short and/or long distance gerianum, Broussonetia papyrifera, Hypericum ascyron, (Chou et al., 2005; Tan and Li, 2009; Tseng and Tso, Nerium indicum, Pyracantha fortuneana, Senecio scan- 2009; Tan et al., 2010). dens), 10 pieces of dry leaves for each of three plants All these results suggested that, at least in certain (Cinnamomum camphora, Nerium indicum, Sabina species, the nonsilk decorations may make the spiders chinensis cv. kaizuka) and 10 pieces of bark for each of more difficult to detect by predators. However, there is three species (Paulownia sp., Pinus massoniana, Sabina empirical evidence that the nonsilk decorations of Cyc- chinensis cv. kaizuka) from the same sites where spiders losa render the spiders webs more conspicuous, and and their decorations were collected. redirect the attacks of predators to the decorations in- 1.2 Spectral reflectance measurements stead of spiders (Chou et al., 2005; Tseng and Tso, We measured the spectral reflectance of both juvenile 2009). Thus, the camouflage function and underlying and adult female C. octotuberculata spiders and their mechanisms of nonsilk decorations built by Cyclosa decorations following standard protocols (Lim and Li, need further investigation. Moreover, while this camou- 2006; Tan and Li, 2009), and only the essential details flage is intuitively obvious to human observers, whether are given here. To collect the spectral reflectance data, a predator detects but ignores the spider or is simply we used an Ocean Optic USB2000 spectrometer (Ocean unable to detect it remains to be tested. Optics Inc., Dunedin, Florida, USA) with a DH-2000 In this study, using Cyclosa octotuberculata (Fig. 1A), deuterium and tungsten halogen light source (Ocean a common detritus-decorating species in East Asia in- Optics Inc., Dunedin, USA). The reflectance reading cluding China, Japan and Korea (Platnick, 2010), we (300–700 nm) was recorded from a circular spot (di- assessed whether predators can distinguish web decora- ameter 1 mm) on the sample (spider or decoration), W. GAN et al.: Function of detritus decorations 381

Fig. 1 Cyclosa octotuberculata and its web decorations A. Close-up of a female sitting at hub and facing down. B. Spider on a web without decorations. C. Spider at hub with a linear decoration of prey remains. D. Spider with a linear decoration consisting of moult, plant detritus and prey remains. E. Spider at hub with a linear eggsac (arrows) decoration. perpendicular to and 2 mm above the sample. Eight can only be detected by a visual system with at least two spots were randomly chosen from each spider (four on types of photoreceptors. In order to evaluate how spider carapace and four on abdomen) and for each decoration. body and web decorations were viewed by predatory We took five repeat readings for each spot. A total of 30 insects and birds, the neuroethological models develo- C. octotuberculata spiders and their respective webs ped for blue tits Parus caeruleus and honeybees Apis were collected and transported back to the laboratory for mellifera were used for computation of colour contrasts. measurements. Ten juvenile spiders were with detritus We chose blue tits and honeybees as model predators for decorations, 10 adult female spiders with detritus deco- a several reasons. First, wasps and passerifrom insec- rations, and 10 adult female spiders with their egg-sac tivorous birds were the potential predators appearing in decorations. In addition, we measured the spectral re- the vicinity of the webs (W.J. Gan, personal observa- flectance of 60 pieces green leaves from six plant spe- tions). Second, the spectral sensitivities of wasps’ pho- cies, 30 pieces of dry leaves from three plants, and 30 toreceptors are similar to those of honeybees (Briscoe pieces of bark from three species collected from the and Chittka, 2001). Finally, the visual sensitivities of same sites where spiders and their decorations were Hymenoptera and blue tits have been commonly used to collected. Five readings were taken at a distance of 2 interpret the perception of web decorations by predatory mm above the leaf or bark for each leaf or bark. The wasps and birds of spiders (e.g., Blackledge and Wenzel, mean spectral reflectance of each background and of the 2001; Théry and Casas, 2002; Bruce et al., 2005; Chou mixed of three backgrounds was used in the calculation et al., 2005; Théry et al., 2005; Cheng and Tso, 2007; of colour contrasts of spider body and web decorations Tseng and Tso, 2009; Tan and Li, 2009; Tan et al., (see below). 2010). We used spectral sensitivity functions of stan- 1.3 Modelling visual systems and colour contrasts dard photoreceptors to calculate photoreceptor excita- Colour contrast is referred to as the contrast caused tions for each measured spectrum (see below). As by the spectral difference between two adjacent objects photoreceptor nomenclature is varied (Kelber et al., (e.g., Chittka, 1992, 1996; Kelber et al., 2003), which 2003), and for purposes here they will be further re- 382 Current Zoology Vol. 56 No. 3 ferred to based on the part of the spectrum to which (Goldsmith, 1990), the coordinates of each spectrum they are absolutely or relatively most sensitive – ‘red’, was calculated as: ‘green’, ‘blue’ or ‘UV’. 22 xEE=°−cos 30 ( ) We calculated the sensitivity factor R for each photo- 3 Green Red receptor as: 1 y=EEEEUV−++ ( Blue Green Red ) RISD= 1/700 ()()λ λλλ ()d 3 ∫ 300 B 22 zEEE=°+−[sin 30 ( ) ] Where IB (λ) is the spectral reflection function of vari- 3 Green Red Blue ous backgrounds collected in the study sites of C. octo- The chromatic contrast between each pair of spider tuberculata. S(λ) is the spectral sensitivity function of and decoration for the tetrahedron vision was then esti- the receptor in question, while D(λ) is the illuminating mated as the Euclidean distance ΔSt: daylight spectrum CIE D65 because spiders were active 222 in normal daylight. We then calculated the effective Δ=St() Δ x +Δ+Δ () y () z quantum flux P for a given spectra in the respective We then compared the calculated colour contrasts photoreceptor as with optimal discrimination thresholds of bird and hymenopteran predators in their particular colour space PR= 700 I()()λ Sλλλ D ()d ∫ 300 S (Théry et al., 2005). Chromatic contrasts were utilized

Where IS (λ) is the spectral reflection function of the for short-range detections. For a honeybee, colour dis- spiders or their respective decorations. When the maxi- crimination is a function of wavelength with an optimal mum excitation Emax of the photoreceptor was normal- resolution of 5 nm around 500 nm (von Helversen, ised to unity, we calculated the physiological receptor 1972). The minimal Euclidean distance of colour con- voltage signals EUV, EB and EG for each photoreceptor trast discrimination or a contrast threshold of wasps is as: 0.05 (Théry and Casas, 2002; Théry et al., 2005). E=P/(P+1) Meanwhile, the contrast threshold for blue tits is 0.06 The coordinates of each spectrum in the colour space (Théry and Casas, 2002; Théry et al., 2005). The colour of various photoreceptors were then calculated differ- contrast for each pair of spider and decoration was then ently according to the types of predators. For the hy- compared to the hymenopteran and bird predator dis- menopteran colour vision, each colour locus was calcu- crimination thresholds using one-sampled t tests to ob- lated using the model by Chittka et al. (1994) and the tain a measure of individual colour mimicry in the spectral sensitivity functions of standard photoreceptors separate visual systems. for trichromatic Hymenoptera were as from Chittka Honeybees and birds have been documented to use (1996). Next, the coordinates of each spectrum in the achromatic contrast at long range or to detect small ob- colour hexagon was calculated using receptor excita- jects (Osorio et al., 1999a, b; Spathe et al., 2001). For tions as detection at longer distances, honeybees use green receptors while birds use double-cones that combine the x = sin 60°(EG − EUV) absorbance spectra of the medium and long wavelengths y = EB − 0.5(EUV + EG) sensitive photoreceptors (Giurfa et al., 1997; Giurfa and The chromatic contrast between each pair of spider and decoration was estimated using the Euclidean dis- Vorobyev, 1998; Hart el al., 2000; Spathe et al., 2001). Achromatic contrasts were calculated using the value of tance ΔSt: green or double-cone photoreceptor signals when ex- 22 Δ=St() Δ x +Δ () y cited by spiders, divided by the corresponding values The spectral sensitivities of blue tit were used to cal- for the web decorations (Théry and Casas, 2002; Théry culate the colour locus of spiders and their decorations et al., 2005). By comparing with the value of 1.0 as pre- as seen by a tetrachromatic passeriform insectivorous dicted for equal brightness using one-sampled t tests, bird (Bowmaker et al., 1997; Vorobyev et al., 1998). the achromatic contrast of the spiders with respect to The sensitivity factor R, effective quantum flux P, exci- their web decorations was evaluated. Therefore, values tation of each photoreceptor, E, was calculated as above of achromatic contrast higher than 1.0 indicate that spi- for bees but with the substitution of blue tit’s spectral ders are brighter than are web decorations, whereas sensitivities (Hart et al., 2000; Hart, 2001). Also, as values lower than 1.0 show that spiders are darker than birds have a colour space in the shape of a tetrahedron are web decorations (Théry et al., 2005). All statistical W. GAN et al.: Function of detritus decorations 383 analyses were performed with SPSS version 11.0 for Neither hymenopteran or bird predator models were Macintosh. able to discriminate C. octotuberculata from either de- 2 Results tritus or eggsac decorations over a short distance, as the chromatic contrast values were significantly lower or The web decorations and C. octotuberculata spider not significantly higher than the detection thresholds of body surfaces had similar reflectance spectra (Fig. 2A). hymenopterans (0.05) and birds (0.06) when viewed The reflectance spectra of juvenile, adult female spiders, against any background (Fig. 3A, C, E; Table 1). Simi- eggsac decorations built by gravid females, and detritus larly, at a distance, spiders would not be discriminated decorations spun by both juvenile non-gravid adult fe- from web decorations by hymenopteran or bird preda- males have low reflectance at short wavelengths and tors since spiders were as bright as their detritus decora- slightly higher reflectance at long wavelengths. All the tions or darker than their egg-sac decorations to both spectra extended to the UV range. Dry leaves and bark hymenopteran and bird predators over long distances had similar reflectance spectra, but green leaves of dif- when viewed against any background (Fig. 3B, D, F; ferent plants had two peaks, a small peak in the UV Table 2). range (320 nm) and a large peak at about 580 nm (Fig. 2B). The blended background (i.e., mean reflectance of 3 Discussion all three different backgrounds) had a more or less This study was designed to investigate whether in- similar spectrum to those of dry leaves and bark (Fig. vertebrate and vertebrate model predators could distin- 2B). guish between Cyclosa spiders and the detritus and eggsac decorations added by spiders to their webs using spectrophotometric anayses. Our results clearly show that theoretically, the addition of prey remains, plant debris and/or egg sacs to webs by C. octotuberclata make spiders more difficult to detect over short and long distances by hymenopteran (e.g., wasps) and bird predators. These patterns are consistent for both detritus (prey remains, moult and plant debris) and eggsac decorations, for decorations constructed by both juvenile and adult spiders, as well as for four common natural backgrounds. Our spectrophotometric analyses suggest that detritus and eggsac decorations of C. octotuberculata may conceal spiders from predators by reducing the spider’s risk of becoming detected over short and long distances. Our spectrophotometric analyses unambiguously indicate that hymenopteran and bird predators cannot distinguish spiders from their detritus or eggsac decorations over short and long distances, but the responses of natural predators to decorations built by different species or populations in different habitats may be different. Using field manipulative experiments and modelling Fig. 2 Normalized reflectance spectra of Cyclosa octotubercu- visual systems of potential prey and predators, Chou et lata spiders, decorations and vegetation backgrounds al. (2005) tested the function of prey-remains as decora- A. Reflectance spectra of juvenile spiders (Juv-Spider; n = 10) and tions built by C. confusa from Taiwan. Their results their detritus decorations (Juv-Detritus; n =10), adult spiders (Adu-Spider: n = 10) and their detritus decorations (Adu-Detritus; n = from modelling visual systems of hymenopteran preda- 10), as well as eggsac decorations (Gra-Eggsac; n = 10) built by tors showed that predators are unable to discriminate the gravid adult spiders (Gra-Spider; n = 10). B. Reflectance spectra of chromatic signals of prey remains from those of spiders. different backgrounds (green leaves: n = 60; dry leaves n = 30; bark, n However, they found that while undecorated webs ex- = 30; blend, n = 120). Error bars are omitted for clarity. Each spectral reflectance reading was normalized to the highest point of the same perienced fewer attacks from predatory wasps Vespa af- reflectance curve. finis, and webs decorated with prey-remains experienced 384 Current Zoology Vol. 56 No. 3

Fig. 3 (A) The mean (± SE) chromatic and (B) achromatic contrasts of detritus decorations built by juvenile Cyclosa octotuberculata against different background types (green foliage, dry leaves, bark and mixed or blend) viewed by bird (blue tits) and hymenopteran predators; (C) The mean (± SE) chromatic and (D) achromatic contrasts of detritus decorations built by adult C. octotuberculata against different background types (green foliage, dry leaves, bark and mixed or blend) viewed by bird (blue tits) and hymenopteran predators; (E) The mean (± SE) chromatic and (F) achromatic contrasts of egg-sac decorations built by adult C. octotuberculata against different background types (green foliage, dry leaves, bark and mixed or blend) viewed by bird (blue tits) and hymenopteran predators Dashed lines indicate thresholds for colour contrast detection calculated for Hymenoptera and birds.

Table 1 Summary of one-sample t-tests comparing the chromatic contrast values of detritus (prey remains, moults, and plant debris) and eggsac decorations built by Cyclosa octotuberculata juvenile and adult spiders against different backgrounds viewed by hymenopteran and bird predators with the discrimination threshold of honeybees (0.05) and blue tits (0.06)

Decoration/spider body against different Decoration/spider against different Comparisons Statistics backgrounds viewed by a hymenoteran predator backgrounds viewed by a bird predator Blend Green leaves Dry leaves Bark Blend Green leaves Dry leaves Bark

Juvenile – Detritus t9 −3.327 −3.996 −3.095 −3.108 −4.471 −5.261 −4.229 −4.229 decorations P 0.013* 0.005** 0.017* 0.017* 0.003** 0.001** 0.004** 0.004**

Adult – Detritus t9 −1.441 −1.913 −1.291 −1.286 −2.312 −2.802 −2.222 −2.173 decorations P 0.193 0.097 0.238 0.239 0.054 0.026* 0.062 0.066

Adult - Eggsac t9 −4.462 −5.603 −4.001 −4.039 −4.740 −5.965 −4.394 −4.352 decorations P 0.003** <0.001*** 0.005** 0.005** 0.002** <0.001*** 0.003** 0.003** W. GAN et al.: Function of detritus decorations 385

Table 2 Summary of one-sample t-tests comparing the achromatic contrast values of detritus (prey remains, moults, and plant debris) and eggsac decorations built by Cyclosa octotuberculata juvenile and adult spiders against different backgrounds viewed by hymenopteran and bird predators with the value of 1.0 (the equal brightness)

Decoration/spider body against different Decoration/spider against different Background Statistics backgrounds viewed by a hymenoteran predator backgrounds viewed by a bird predator Blend Green leaves Dry leaves Barks Blend Green leaves Dry leaves Barks

Juvenile v.s. t9 0.511 0.513 0.509 0.511 0.421 0.422 0.419 0.421 Detritus P 0.625 0.624 0.627 0.625 0.686 0.686 0.687 0.686

Adult v.s. t9 −0.020 −0.020 −0.020 −0.020 −0.139 −0.139 −0.139 −0.139 Detritus P 0.985 0.985 0.984 0.985 0.893 0.894 0.893 0.893

Adult v.s. t9 −2.582 −2.578 −2.587 −2.582 −2.702 −2.700 −2.704 −2.702 Eggsacs detritus P <0.05* <0.05* <0.05* <0.05* <0.05* <0.05* <0.05* <0.05* more wasp attacks, wasps usually attack spiders directly in nature needs to be tested experimentally. on undecorated webs but attack the decorations instead The difference in predation rates by decorated webs of the spider on decorated webs. This suggests that de- from different studies may reflect the different predatory tritus decorations are spun by C. confusa to mislead the behaviour or sensory systems of different wasp species attacking predators. In a recent study of decorations living in different habitats. This is because some constructed by C. mulmeinensis from Taiwan, which are anti-predator defences may only be effective against composed of separate prey pellets and eggsacs that re- particular predators (i.e., Sih et al., 1998) or in particular semble the spider in size and colour, Tseng and Tso habitats (Endler, 1978; Merilaita, 2001; Ruxton et al., (2009) found that webs with more decorations suffered 2004). Alternatively, there might be different forms or increased numbers of attacks by wasps, and argued that mechanisms of camouflage used by nonsilk decorating these pellet-like decorations may act as decoys to dis- Cyclosa spiders. Nonsilk decorations of Cyclosa spi- tract predators and become the focus of predator attack. ders used as camouflage strategies have been often It is apparent that the pellet-like prey remains or eggsac mentioned in previous literature, but it is unclear as to decorations are constructed to direct the attention of the exact mechanistic processes of detritus and eggsac predators from the trait (i.e., appearance; size and colour) decrations of Cyclosa. There are a few possible mecha- that gives away the spider: a camouflage strategy by nisms of camouflage for Cyclosa detritus and egg sac distraction. decorations. The first possible mechanism is back- In a study of the function of prey remains and eggsac ground matching (Cott, 1940; Endler, 1978; Stevens, decorations built by C. mulmeinensis from Singapore, 2007; Stevens and Merilaita, 2009), where the detritus Tan and Li (2009) found that undecorated webs did not decorations are designed by the spider as background so attract more predator attacks than decorated ones, given that the spider’s appearance (size and colours) could that C. mulmeinensis spiders cannot be discriminated match that of decorations (background). This form of from their decorations of prey remains at close prox- camouflage might be what most researchers consider imity and from their eggsac decorations by both wasps the function of nonsilk decorations to be. However, and birds over short and long distances. The same has there is no experimental proof with evidence for the been reported in a recent study testing the function of idea of background matching. The second possible form plant detritus decorations built by C. ginnaga from of camouflage is distraction, where web decorations that China (Tan et al., 2010). No predator attacks were have similar colour patterns as the spider or resemble recorded at all for whether the webs are decorated with the spider in size and colour so that they direct the plant detritus or not (Tan et al., 2010). Thus, whether predator’s attention away from the spider or redirect the predators are unable to detect the spiders, or detect them predator’s attention to the web decorations. The ex- but simply ignore the signals cannot be ruled out (Tan et perimental evidence provided by studies of C. confusa al., 2010). Given that both hymenopteran and bird (Chou et al., 2005) and C. mulmeiensis from Taiwan predators cannot detect C. octotuberculata spiders on (Tseng and Tso, 2009) may suggest this mechanism. The webs decorated with prey remains, plant debris, moult third possible mechanism is disruptive coloration, sug- and/or eggsacs over short and long distances, whether gested by Gonzaga and Vasconcellos-Neto (2005). They these decorations could reduce the predation on spiders used clay spider models and clay decoration models 386 Current Zoology Vol. 56 No. 3 with the same dark color as the clay model spiders and Cheng RC, Tso IM, 2007. Signaling by decorating webs: Luring prey found that clay model spiders had higher number of or deterring predators? Behav. Ecol. 18: 1085−1091. attacking marks than clay decoration models. They thus Chittka L, 1992. The colour hexagon: A chromaticity diagram based on photoreceptor excitation as a generalized representation of co- argue that predators are unable to associate the shape of lour opponency. J. Comp. Physiol. A 170: 533−543. a detritus column with a spider but the finding that the Chittka L, 1996. Optimal sets of colour receptors and opponent proc- addition of columns with a contrasting color was effec- ess for coding of natural objects in insect vision. J. Theor. Biol. tive in reducing the incidence of attacks suggests that 181: 179−196. detritus columns may achieving lower attacks via Chittka L, Shmida A, Troje N, Menzel R, 1994. Ultraviolet as a component of flower reflections, and the colour perception of Hymen- breaking the outline of the spider’s body. Finally, detri- optera. Vision Res. 34: 1489−1508. tus and eggsac decorations may conceal spiders by both Chou IC, Wang PH, Shen PS, Tso IM, 2005. A test of prey-attracting masquerade and distraction, and prevent recognition and predator defence functions of prey carcass decorations built by (Cott, 1940; Stevens, 2007; Stevens and Merilaita, Cyclosa spiders. Anim. Behav. 69: 1055−1061. 2009). Detritus and eggsac decorations are constructed Cott HB, 1940. Adaptive Coloration in Animals. London, UK: Methuen & Co. 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