2006. The Journal of 34:427–434

THE FEATURES OF CAPTURE THREADS AND ORB-WEBS PRODUCED BY UNFED CYCLOSA TURBINATA (ARANEAE: ARANEIDAE)

Sarah C. Crews: ESPM-Division of Biology, University of California Berkeley, 140 Mulford #3114, Berkeley, California 94720-3114 USA. E-mail: [email protected] Brent D. Opell: Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 USA

ABSTRACT. Orb-webs constructed by members of the family Araneidae are composed of sticky and non-sticky threads deposited in a stereotypic fashion. This study examines how changes in a spider’s nutritional condition affect the capture thread properties and architectural details of its web. It does so by characterizing the features of successive webs constructed by unfed that were not allowed to recycle previous webs. The volume of a capture thread’s viscous material and the threads’ inferred stickiness decreases in successive webs, although the capture thread’s extensibility does not change. The lengths of both capture thread and non-sticky thread decrease at similar rates in successive webs. The decreasing stickiness of capture threads reduces the stickiness per unit capture area. We did not detect asymmetry in the spacing of either spiral or radial threads of first and last webs, nor did we observe differences in the sizes of viscous droplets in outer and inner spiral turns. This suggested that these spiders assessed their silk resources before they initiated web construction and altered their behavior to produce a highly regular web of an appropriate size for their silk reserves. Keywords: Nutrition, hunger, silk allocation, spider, thread extensibility, thread stickiness

Orb-webs constructed by members of the thought to make the thread sticky (Vollrath et orbicularian subclade Araneoidea are highly al. 1990; Vollrath & Tillinghast 1991; Vollrath integrated structures formed of the products of 1992; Tillinghast et al. 1993; Peters 1995). three spinning glands that independently draw Hydrophilic compounds in the viscous mate- their components from a common hemolymph rial attract atmospheric moisture to maintain pool (Foelix 1996). Non-sticky threads pro- the thread’s water content (Townley et al. duced by ampullate glands form the web’s an- 1991; Edmonds & Vollrath 1992), which ac- chor, frame, hub, and radial threads. The spi- counts for about 80% of its volume (Gosline rally arrayed, sticky prey capture thread is et al. 1986). produced by two spinning glands. The flagel- Non-sticky thread usually comprises the liform spigot on a posterior lateral greater proportion of an orb-web’s total thread produces a supporting axial fiber and the two length. Eberhard (1988a) estimates that sticky adjacent aggregate spigots coat this fiber with thread typically forms 36–54% of the total a viscous aqueous solution. Material from the length of thread in an orb-web but that it is two posterior lateral merge and the responsible for a greater percentage of an orb- viscous solution coalesces into a series of web’s mass because it has a greater volume droplets. These droplets are formed of a com- per length than does non-sticky thread. This plex solution of organic and inorganic com- may suggest that supplies of capture thread pounds, a variety of small proteins, and high precursors limit an orb-web’s size. However, molecular weight glycoproteins (Townley factors such as silk gland sizes, the efficiency 1990; Vollrath et al. 1990; Townley et al. with which glands extract precursors from the 1991; Vollrath & Tillinghast 1991; Vollrath hemolymph, and the metabolic cost of pro- 1992; Tillinghast et al. 1993). Glycoprotein ducing threads affect a spider’s ability to pro- nodules form within each droplet and are duce threads.

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Orb-web architecture results from an inter- was being depleted, spiral spacing might in- action between the spider’s innate web-build- crease in successive (more central) spiral turns ing behavior, the environment, and the spi- or the size of the capture thread’s viscous der’s silk resources. Web features such as droplets might also decrease centrally. capture area, number of radii, and spiral spac- To examine the effect of nutritional deficit ing exhibit intraspecific plasticity (Witt & on orb-webs and their threads, we measured Baum 1960; Eberhard 1988a). The effects of the features of successive threads and webs a spider’s nutritional condition may contribute produced by unfed spiders. Our investigation to this variability. Several studies report that expands an earlier study (Witt 1963) by ex- as spiders became heavier the spiral spacing amining a different species and by measuring of their web increases (Witt & Baum 1960; the web and thread features of the same spi- Christiansen et al. 1963; Witt 1963). ders over time, rather than comparing the fea- Poor nutrition may affect web architecture tures of one group of fed spiders and another in two ways. It may limit the supply of a spi- group of starved spiders. To further limit a der’s total silk protein, thereby reducing the spider’s silk resources, we also removed most lengths of all web elements, or it may also of the silk from a web before it could be re- limit the length of all or some web elements cycled. These procedures allowed us to test by restricting one or more critical amino acids the hypothesis that the length of sticky thread or other web compounds (Higgins & Rankin declines more rapidly than non-sticky thread, 1999). and to examine the influence of diminishing Many spiders, including the species used in nutritional resources on the volume, extensi- this study (pers. obs.), ingest silk and sticky bility, and inferred stickiness of viscous droplets as they take down their webs and re- thread. It also permitted us to further test the cycle this material in the new webs they con- hypothesis (supported by Witt et al. 1968) that struct (Carico 1986). This improves the econ- a spider assesses its silk resources before be- omy of orb-web use; estimates of reuse of ginning web construction and uses this infor- organic orb-web constituents range from 32– mation to alter its silk allocation and web ar- 97% (Breed et al. 1964; Peakall 1971; Town- chitecture, thereby maintaining uniform ley & Tillinghast 1988). Using the most con- spacing of web elements and conserving crit- servative of these estimates, Opell (1998) ical elements of web design. concluded that web recycling reduced the cost of orb-web construction by about 32%. If web METHODS production is limited by certain amino acids Species studied.—We studied adult female and other compounds critical for web produc- Cyclosa turbinata (Walckenaer 1842), collect- tion, then web recycling may have even great- ed from June to August 1999 on the Virginia er benefits. Polytechnic Institute and State University A spider could accommodate diminishing campus, and surrounding areas of Blacksburg, supplies of thread precursors in two ways Montgomery County, Virginia (N 37.22874, (Witt et al. 1968; Eberhard 1988a): 1. Evalu- W 80.42558). At the end of the study, spiders ate silk supplies prior to web construction and were preserved in 70% ethanol and identified alter the design of the entire web or 2. Re- using Levi (1977). Voucher specimens are de- spond to dwindling silk supplies as they are posited in the Museum of Comparative Zo- encountered during web construction. In the ology. first case, if non-sticky silk reserves were low, Experimental design.—Whenever possi- a spider might construct a smaller outer frame ble, the stabilamentum was collected along that would reduce web area and minimize with the spider and suspended from a support changes in the number of radii. If capture in the container in which the spider was thread reserves were low, increased spiral housed, as this encouraged web building spacing could maintain a uniform stickiness- (Rovner 1976). Spiders were kept in 25 ϫ 37 per-web-capture-area ratio, but would alter the ϫ 12 cm plastic boxes set upright on their web’s radius-to-spiral-turn ratio. In the second longest sides. Wooden dowel rods 5 mm in case, a severe reduction in non-sticky thread diameter were glued around the perimeter of during frame construction might result in the box to serve as web attachment sites. The more widely spaced radii. If capture thread side of the box opposite the lid was removed CREWS & OPELL—CYCLOSA TURBINATA THREAD AND WEB FEATURES 429 and covered with plastic food wrap to allow along two radii in each web. From this, the easy access to the webs. The boxes provided mean inner and outer spiral spacing was com- ample space to accommodate the webs that C. puted. We measured (along the same spiral turbinata produce under natural conditions. turn) the distance between each of three radii The boxes were kept in an environmental to the left and three radii to the right of these chamber with a 13:11 h dark-light cycle, a two reference radii and computed mean radius temperature of 25Њ C and a relative humidity spacing. of 80%. Thread features.—The features of sticky We examined spiders daily and, after thread thread samples taken from the outer- and in- samples were collected or a web was photo- ner-most 1–4 spiral turns of a web were mea- graphed, we destroyed most of the web and sured. These samples were collected by care- removed most of its silk, leaving only the sta- fully placing calipers whose tips were coated bilamentum and a few framework lines and with double-sided tape against a thread and radii to encourage the spider to construct an- then cutting this portion from the web with other web. After its web was destroyed, each small scissors. From each sample, we mea- spider was given an opportunity to drink by sured the lengths and widths of two droplets placing it on water-saturated cotton. If a spider from each of two different thread segments did not make a web after 3 or 4 days, it was and, from the same regions of the thread, the released. distance spanned by a series of droplets (mean Spiders were divided into two groups that number droplets ϭ 17.5 droplets). When drop- were sampled on alternate days. Of the spiders let size differed within a segment, we mea- we placed in boxes, eight produced enough sured the dimensions of one of the smaller and webs to be included in comparisons of webs one of the larger droplets. From these mea- and ten produced enough webs to be included surements, droplet volume (␮m3) per mm was in thread comparisons. Every 48 hours, webs calculated using the formulas given by Opell constructed by one group of spiders were (1997). We evaluated the regularity of viscous dusted with corn starch (Carico 1977) and droplet size and spacing in the first and last photographed. Uncontaminated capture threads webs constructed by ten spiders that produced were collected from webs produced by the the greatest number of webs by comparing the other group of spiders. The webs constructed droplet features of their outer and inner spiral by spiders of each group were numbered se- turns. quentially. As many as 21 webs were made The stickiness of an adhesive capture thread by individual spiders whose webs were dusted can be estimated from the volume of the and as many as 30 webs by individual spiders thread’s droplets (Opell 2002). This volume is whose threads were collected (mean numbers computed from measurements of droplet 12.4 and 13.8 respectively). length, width, and distribution (Fig. 2 & For- Web features.—Boxes containing dusted mulas 1–4 in Opell 2002). The thread mea- webs were elevated above a black cloth and the webs were photographed from a distance surements used to compute this volume are ϳ0.7 m. A reference measurement was re- shown in Figure 2 of Opell (2002). We used corded and, after printing enlarged photo- the data from this earlier study to develop a graphs, used to compute an enlargement index formula to estimate the stickiness of capture for each web photograph. From these mea- threads produced by adult C. turbinata. This surements, the lengths of sticky and non- was done by regressing the volume of thread sticky threads, spiral spacing, and the total droplets per mm of thread length against ϭ area and capture area of webs were deter- thread stickiness to obtain the significant (n ϭ ϭ 2 ϭ mined using the formulas given in Opell 17, F 11.16, P 0.0041, R 0.41) for- (1997). mula: We evaluated the regularity of spiral spac- Stickiness (␮N/mm thread contact) ing and radial line distribution in the first and last webs constructed by the six spiders that ϭ droplet volume (␮m3 ) per mm produced the greatest number of webs. We ϫ 0.000221 measured the distance between the six outer- most and between the six inner-most spirals ϩ 4.87. 430 THE JOURNAL OF ARACHNOLOGY

ϭ ϭ Table 1.—Comparison of thread features. LB thread length at breaking, LI initial thread length. Values are reported as mean Ϯ 1 standard error. The mean number of webs in each of the three categories is presented in the first row. The P values of repeated ANOVA’s are given for the complete model and separately for the three web orders and the ten spiders whose values were included. An * denotes features that we consider to show change by virtue of significant model and order (web sequence) P values and consistently increasing or decreasing mean values.

Webs 1–3 Webs 4–7 Webs 8–30 ANOVA P Values n ϭ 15, n ϭ 12, n ϭ 26, (Model, Order, X ϭ 1.9 Ϯ 0.3 X ϭ 5.6 Ϯ 0.3 X ϭ 13.9 Ϯ 1.1 Spider) Droplet Diameter (␮m) 9.68 Ϯ 1.00 7.17 Ϯ 0.40 5.68 Ϯ 0.31 * 0.000, 0.000, 0.035 Droplets per mm 38.7 Ϯ 2.9 42.0 Ϯ 3.6 55.5 Ϯ 3.4 * 0.008, 0.001, 0.139 Total Droplet Volume (␮m3 /mmϫ 103) 17.52 Ϯ 4.28 9.17 Ϯ 1.79 6.71 Ϯ 1.47 * 0.047, 0.000, 0.241 Ϯ Ϯ Ϯ Extensibility (LB /LI) 4.14 0.38 3.26 0.34 3.86 0.32 0.048, 0.563, 0.039

We then computed estimated stickiness val- iance (RMANOVA) test to examine differ- ues for each of the undusted web samples of ences among the values of thread and web the current study and regressed these sticki- features. Spiders could (and did) make more ness values against the sequential numbers of than 1 web in each of the three web groupings the webs from which these threads were taken that we used, which is one reason we used the to obtain the significant (n ϭ 51, F ϭ 15.26, RMANOVA and also accounts for sample siz- P ϭ 0.0003, R2 ϭ 0.23) formula: es being greater than the total number of spi- Stickiness (␮N/mm thread contact) ders used. The RMANOVA model included two components: web sequence and spider. ϭϪ1.2742 natural log web number The former accounted for changes in nutri- ϩ 9.4346. tional condition and the latter for inter-indi- vidual variability. We consider as significant Using this formula, we assigned a stickiness only those values whose increase or decrease value to the threads in each of the dusted was marked by the following: 1. a significant webs. As these were the webs for which we (P Յ 0.05) overall model; 2. a significant web measured thread lengths, this permitted us to sequence model component; and 3. a consis- estimate the total stickiness of the webs’ cap- tent (non-oscillating) change in the value in ture threads and the stickiness per web capture question. If, for example, the first two require- area. ments were met but an index showed a reduc- After the droplets on the threads were mea- tion in the Webs 4–7 sequence but an increase sured, the thread was placed on the tips of in the Webs 8–30, we attributed this oscilla- digital calipers covered with double sided tape tion to a cause other than declining nutritional and opened to a distance of 2.5 mm. A motor condition. Paired t-tests were used to compare separated the tips of the calipers at a rate of spiral and radial spacing and capture thread 17 ␮m per second. When the thread broke, the droplet features. Statistical tests were per- motor was stopped and the distance the cali- formed with SAS for the Power Macintosh pers had spread was recorded. Extensibility computer (SAS Institute, Cary, North Caroli- was then computed as a ratio of the breaking na). length of a thread to its initial length. Statistical analyses.—We included in our RESULTS analyses of threads only spiders that con- structed at least 9 webs (mean number of Thread features.—Mean droplet diameter webs ϭ 13.3) and in our analysis of webs only decreased and mean droplet number per mm spiders that constructed at least 7 webs (mean increased in subsequent webs (Table 1). The number of webs ϭ 10.3). We divide webs into net result was a decrease in droplet volume three sequential groups (e.g., for thread fea- per mm of thread, with the mean value for tures: Webs 1–3, Webs 4–7, and Webs 8–30) webs in the last group being only 38% that of and used a repeated measures analysis of var- the webs in the first group. In contrast, thread CREWS & OPELL—CYCLOSA TURBINATA THREAD AND WEB FEATURES 431 Values P Spider) (Model, Order, ANOVA values and consistently increasing P 1.1 Ϯ 20, 20.7 [18]94.3 [18]111.5 [18]84.1195.4 0.026, * [18] 0.065, 0.000, 0.329 * 0.014,0.1 0.001, 0.011 [18] 0.012, 0.019 0.05 [18] *0.04 0.001, [18] 0.007, 0.054 *0.7 0.003, 0.006, 0.113 0.07 0.033, 0.434,1.5 0.013, 0.047 [19] 0.080, 0.015 0.05 0.003, [19] 0.072, 0.003 7.67.1 * 0.002, 0.004,588 0.126 0.000, 0.000, 0.073, 0.085,7.5 0.001, 0.005 0.000 0.016, 0.000 0.147, 0.116, 0.171 * 0.130, 0.000, 0.111, 0.000, 0.143 0.111 * 0.000, 0.000, 0.004 ϭ 11.6 Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ n ϭ Webs 7–21 X 0.2 Ϯ 8, 22.0 [7]117.3 [7]106.2 [7]96.1195.7 [7]0.4 409.9 1287.1 [7]0.08 1697.0 [7]0.06 [7]1.2 2937.1 1273.6 0.011.3 [7] 3.10 0.11 [7] 1.40 10.0 1.05 9.87027.6 18.9 2.11 34.4 1.83 87.2 80.9 8191 108.8 ϭ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ 4.9 n ϭ Webs 4–6 1 standard error. The mean number of webs in each of the three categories is X Ϯ 0.3 Ϯ 9, 39.9 [8]250.6 [8]277.5 [8]216.2 [8]488.5 [8]0.4 [8] 491.4 1797.1 0.05 [8] 2288.6 0.05 [8] 1662.6 1.4 3958.2 0.063.3 [8]0.09 [8] 3.73 1.39 14.3 1.08 13.4211610.4 21.9 2.01 42.1 1.97 106.0 98.0 12341 130.5 ϭ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ Ϯ 2.1 n ϭ Webs 1–3 X ) 179.5 2 N/cm ) 109.6 ␮ 2 ) 101.2 2 values of repeated ANOVA’s are given for the complete model and separately for the three web orders and the ten spiders whose values were P Table 2.—Comparison of web features. Values are reported as mean or decreasing mean values. included. An * denotes features that we consider to show change by virtue of significant model and order (web sequence) presented in thebrackets. first The row. When the sample size differs from that reported immediately under each of the three web sequences, this number is reported in Frame Length (cm) 552.3 Radii Length (cm)Non-capture Length (cm)Capture Length (cm)Total Thread Length (cm)Radii Length/Frame LengthNon-capture/Capture LengthRadii Length/Capture LengthSpiral TurnsSpiral Spacing 2579.3 (mm)Number of RadiiRadii 2027.0 per 4684.5 Spiral TurnTotal 2026.4 Web Area 3.64 (cm Capture 1.24 Area (cm Total 0.96 Stickiness (mN)Stickiness per Area ( 1.73 25.2 1.77 45.5 17562 432 THE JOURNAL OF ARACHNOLOGY

Table 3.—Indices of web regularity. The mean Table 4.—Indices of droplet regularity. The mean number of webs in each of the two categories is number of webs in each of the two categories is presented in the first row. Values are reported as presented in the first row. Values are reported as mean Ϯ 1 standard error. P values are for paired t- mean Ϯ 1 standard error. P values are for paired t- tests. tests.

First Web Last Web First Web Last Web n ϭ 6, n ϭ 6, n ϭ 10, n ϭ 10, X ϭ 2.0 Ϯ 0.6 X ϭ 11.8 Ϯ 2.2 X ϭ 1.2 Ϯ 0.1 X ϭ 13.3 Ϯ 1.4 Radii Spacing: Droplet Diameter: Right (mm) 7.93 Ϯ 0.47 7.13 Ϯ 0.56 Outer (␮m) 11.13 Ϯ 1.04 5.43 Ϯ 0.39 Left (mm) 8.42 Ϯ 0.40 7.31 Ϯ 0.72 Inner (␮m) 10.69 Ϯ 2.39 4.56 Ϯ 0.45 P 0.099 0.637 P 0.853 0.066 Spiral Spacing: Droplets per mm: Outer (mm) 1.95 Ϯ 0.20 2.08 Ϯ 0.13 Outer 28.33 Ϯ 3.51 51.09 Ϯ 4.14 Inner (mm) 1.95 Ϯ 0.16 2.00 Ϯ 0.14 Inner 43.17 Ϯ 5.88 76.35 Ϯ 9.80 P 0.928 0.177 P 0.070 0.012

DISCUSSION extensibility did not change in successive Cyclosa turbinata exhibited a surprising webs (Table 1). ability to continue constructing orb-webs in Web features.—Although frame thread the absence of both new resources and recy- length declined during the study this differ- cled material from previous webs. Reduced ence was not significant (Table 2). However, metabolic rate induced by starvation (Ander- the lengths of all other web elements dimin- son 1974) and the elimination of bouts of prey ished by 34–37% in subsequent webs (Table capture may help extend a spider’s resources. 2). The surprising uniformity of this decline The lengths of both capture threads and non- is also documented by the failure of web order sticky threads decreased in subsequent webs, to explain differences in the ratios of radii but we found no support for the hypothesis thread to frame thread lengths, non-capture to that capture thread length decreased more capture thread lengths, and radii to capture quickly than non-sticky thread length. It is thread lengths. The decline in capture thread possible that frame thread length did not de- length was reflected in a decreased number of crease significantly because, when leaving spiral turns, although this was not accompa- web remnants to encourage spiders to re-build nied by an increase in spiral spacing. The their webs, we may have left proportionately number of radii did not diminish. Total web more non-sticky threads than sticky threads. Due to the subjectivity of this procedure, we capture area did not decrease. However, as a are unable to assess this possibility. However, consequence of declining capture thread vol- we believe that we left so little silk that it had ume per mm of thread length (Table 1), total a minimal effect. The maintenance of a fairly estimated web stickiness decreased by 47%. stable ratio of these two thread types may be This was associated with a 32% decrease in explained by the decrease in the volume of 2 the estimated stickiness per cm of web cap- viscous material covering the capture threads. ture area. Rather than compensating for diminishing The spacing of radii and capture spirals capture thread reserves only by reducing cap- showed no irregularity in first or last webs ture thread length, C. turbinata reduces both (Table 3) and, therefore, provided no evidence capture thread length and capture thread vol- of diminishing intra-web silk resources. Outer ume. This may help explain why the observed spirals tended to have larger droplets that were decrease in web capture area was not signifi- more closely spaced than inner spirals (Table cant. In contrast, in studies using 4). However, the only significant difference spp., Witt (1963) found that web diameter de- was in the droplet distribution of the last webs creased and spiral spacing increased after 10 constructed. and 17 days of starvation. The regularity of CREWS & OPELL—CYCLOSA TURBINATA THREAD AND WEB FEATURES 433 radii and capture spirals in C. turbinata webs LITERATURE CITED supports the hypothesis that a spider can as- Anderson, J.F. 1974. Responses to starvation in the sess its silk resources before constructing a spiders Lycosa lenta Hentz and Filistata hiber- web and, even as these resources decline, con- nalis (Hentz). Ecology 55:576–585. struct a web that has a regular architecture. Breed, A.L., V.D. Levine, D.B. Peakall & P.N. Witt. This agrees with Witt’s (1963) observations 1964. The fate of the intact orb web of the spider on Clerck, 1757. Evi- Araneus diadematus Cl. Behaviour 23:43–60. dence for memory based, compensatory web Carico, J.E. 1977. A simple device for coating orb webs for field photography. Bulletin of the Brit- construction behavior has been noted in orb- ish Arachnological Society 4:100. web temporary spiral construction in other Carico, J.E. 1986. Web removal patterns in orb- species (Eberhard 1988b). weaving spiders. Pp. 306–318. In Spiders: Webs, The nutritional independence of the capture Behavior, and Evolution (W.A. Shear, ed.). Stan- thread’s inner axial lines and their viscous ford University Press, Stanford, California. covering is shown by the thread’s unchanging Eberhard, W.G. 1971. Senile web patterns in Ulo- extensibility (attributed to its axial lines) in borus diversus (Araneae: ). Develop- the face of its decreasing viscous volume (Ta- mental Psychobiology 4:249–254. ble 1). Changes in the size and distribution of Eberhard, W.G. 1988a. Behavioral flexibility in orb web construction: effects of silk supply in dif- the thread’s viscous droplets may result from ferent glands and spider size and weight. Journal changes in the chemical composition of this of Arachnology 16:295–302. material or smaller amounts of viscous mate- Eberhard, W.G. 1988b. Memory of distances and rial may alter the dynamics of droplet for- directions moved as cues during temporary spiral mation. Changes in the diameters of axial fi- construction in the spider Leucauge marana (Ar- bers may also influence droplet size. As the aneae: Araneidae). Journal of Insect Behavior 1: thread’s viscous material has both high water 51–66. content (Gosline et al. 1986) and hydrophilic Eberhard, W.G. 1990. Function and phylogeny of spider webs. Annual Review of Ecology and capabilities (Townley et al. 1991), a spider’s Systematics 21:341–372. hydration and the humidity of its environment Edmonds, D. & F. Vollrath 1992. The contribution may affect the features of its capture thread. of atmospheric water vapour to the formation We attempted to control for these factors by and efficiency of a spider’s web. Proceedings of providing spiders with regular access to water the Royal Society of London 248:145–148. and maintaining them and measuring their Foelix, R.F. 1996. The Biology of Spiders. Second threads under uniform conditions. edition. Oxford University Press, New York. 330 Although we attribute the changes in pp. threads and webs that we observed to the de- Gosline, J.M., M.E. DeMont & M.W. Denny. 1986. The structure and properties of . En- clining nutritional states of the spiders, we deavour 10:37–43. cannot entirely rule out the effect of aging. Higgins, L. & M.A. Rankin. 1999. Nutritional re- However, we judge the aging effects to be rel- quirements for web synthesis in the tetragnathid atively minor as our study ended in August, spider Nephila clavipes. Physiological Entomol- and at this locality, C. turbinata adult females ogy 24:263–270. build webs until mid October. Additionally, Levi, H.W. 1977. The American orb-weaver genera the webs we observed were judged symmet- Cyclosa, Metazygia and Eustala North of Mexi- rical by our indices and showed none of the co (Araneae: Araneidae). Bulletin of the Museum of Comparative Zoology 148:61–127. characteristics of ‘‘senile webs’’ that are Opell, B.D. 1997. The material cost and stickiness sometimes built by orb-weaving spiders near of capture threads and the evolution of orb-weav- the end of their lives (Eberhard 1971). ing spiders. Biological Journal of the Linnean Society 62:443–458. ACKNOWLEDGMENTS Opell, B.D. 1998. Economics of spider orb-webs: We are grateful to Dr. William Eberhard, the benefits of producing adhesive capture thread and of recycling silk. Functional Ecology 12: Dr. Mark Townley and Dr. Gail Stratton for 613–624. comments and suggestions that improved this Opell, B.D. 1999. Redesigning spider webs: stick- manuscript. This material is based upon work iness, capture area, and the evolution of modern supported by the National Science Foundation orb-webs. Evolutionary Ecology Research 1: under grants IBN-9417803 and IOB-0445137. 503–516. 434 THE JOURNAL OF ARACHNOLOGY

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