2013 NORTHEASTERN NATURALIST 20(3):419–429
Does Pitcher Plant Morphology Affect Spider Residency?
Marc A. Milne1,2 and Deborah A. Waller2
Abstract - Spiders are often found as residents in association with Sarracenia purpurea
(Purple Pitcher Plant). Many spiders choose web locations based on environmental cues
such as vegetation structure and composition, prey density, temperature, and humidity.
To determine if spiders use cues from the Purple Pitcher Plant to build their webs, we
conducted a field study using variants of the plant that separated various morphological
features: nectar, pigment, and the presence of prey. There was no difference in spider
residency across all treatments and no difference in male/female or mature/immature
residency. Linyphiids were the most common residents, possibly due to pitcher structure
and natural web size.
Introduction
Sarracenia purpurea L.(Purple Pitcher Plant) is a low-lying herbaceous perennial
that uses pitcher-shaped leaves to capture mostly arthropod prey for nutrient
supplementation. Common prey of the Purple Pitcher Plant include invertebrate
taxa such as insects, spiders, harvestmen, mites, mollusks, and the occasional
small vertebrate (Cresswell 1991, Heard 1998, Judd 1959, Lloyd 1942, Wray and
Brimley 1943). Most carnivorous plants have been hypothesized to use morphological
features such as nectar and red pigment to lure prey (Joel 1986, Juniper et
al. 1989, Lloyd 1942, Schnell 2002). Other morphological features that may function
in prey attraction or retention include ultraviolet (UV) reflectance (Joel et al.
1985), decaying insects in the liquid (Schnell 2002), and fragrance (Di Giusto et al.
2008, Juniper et al. 1989), yet many of these features have not been well studied.
However, some studies have shown that red pigment has little effect on prey capture,
because naturally occurring pitcher plants that lack the gene to produce red
pigment (such as S. purpurea ssp. purpurea f. heterophylla (Eaton) Fernald) have
similar capture rates to pigmented varieties (Green and Horner 2007, Sheridan et
al. 2000). Moreover, some studies have concluded that carnivorous plants may rely
heavily on random encounters to catch prey and that these morphological features
merely retain prey on the plant (Williams 1976, Zamora 1995).
Spiders can be separated into two main groupings by their method of prey
capture: web-building spiders and ground spiders (Foelix 2010). When selecting
habitats, many types of spiders choose areas based on prey density (Harwood et
al. 2001, Kareiva et al. 1989, Riechert 1985, Waldorf 1976), vegetation structure
(Duffey 1966, Halley et al. 1996, Post and Riechert 1977, Riechert 1974, Robinson
1981), vegetation composition (Barnes 1953, Post and Riechert 1977), and
abiotic factors such as temperature and humidity (Enders 1977, Riechert 1985,
1Department of Biology, University of North Carolina, Greensboro, NC 27412. 2Department
of Biological Sciences, Old Dominion University, Norfolk, VA 23529. *Corresponding
author - mamilne@uncg.edu.
M.A. Milne and D.A. Waller
2013 Northeastern Naturalist Vol. 20, No. 3
420
Tanaka 1991, Turnbull 1964). The distribution of spiders is also affected by seasonal
changes; population peaks of spiders usually occur in the late spring and
early fall (Barnes 1953, Elliot 1930, Muma and Muma 1949).
Spiders frequently build webs near carnivorous plants and sometimes steal
prey from them (Schnell 2002). Alternatively, one study has shown that spiders
avoid areas of high carnivorous plant (Drosera capillaris Poiret [Pink Sundew])
density to avoid competition (Jennings et al. 2010). However, when living near
the Purple Pitcher Plant, certain spiders of the family Linyphiidae have been
shown to be kleptoparasitic because they spin webs inside of the pitcher and consume
prey that would have otherwise gone to the plant (Cresswell 1991, 1993).
Spiders of the family Lycosidae have been hypothesized to have a commensal
role by using decaying or dead pitchers as oviposition sites (Hubbard 1896, Jones
1935, Milne 2012, Rymal and Folkerts 1982). Finally, the Purple Pitcher Plant
may create a high insect density near the plant, making the immediate vicinity an
appealing spot for spiders’ webs. If spiders seek out pitcher plants, they may use
certain morphological features (e.g., red pigment, nectar, dead insects, structure,
etc.) to find them.
In a field study, we used five manipulated variants and/or models of pitcher
plants that combined one or more of the following cues: red pigment, nectar, and/
or decomposing prey. We then collected spiders residing near these treatments
over three summer months to determine if the morphological features commonly
found on carnivorous plants influence the behavior of spiders to reside nearby.
Field-Site Description
The field site was Old Dominion University's 129-ha (319-acre) Blackwater
Ecological Preserve (BEP; 36.87°N, 76.83°W) in southeastern Virginia. BEP is
a fire-dependent community dominated by Quercus laevis Walter (Turkey Oak)
and Pinus taeda L. (Loblolly Pine), with many herbaceous shrubs and open
spaces with low-lying plants (Frost and Musselman 1987). Pinus palustris Mill.
(Longleaf Pine) is being restored at BEP, which is subjected to prescribed burns
at least once a year. The preserve contained approximately 17 Purple Pitcher
Plant clumps at the time of sampling, between May–July 2008.
Methods
Five different treatments were used in this study: the Purple Pitcher Plant with
no manipulation (containing nectar [N+], red pigment [P+], and water [W+] in
the pitchers; henceforth “N+P+W+”), S. purpurea ssp. purpurea f. heterophylla
with no manipulation (lacking red pigment [P-]; henceforth “N+P-W+”), the
Purple Pitcher Plant with nectar glands covered along the lip (peristome) of the
pitchers (lacking most of the nectar [N-]; henceforth “N-P+W+”), the Purple
Pitcher Plant with cotton placed into the pitchers to prevent prey capture (lacking
water; henceforth “N+P+W-”), and blue polyurethane Purple Pitcher Plant
models (lacking both nectar [N-] and red pigment [P-]; henceforth “N-P-W+”)
421
M.A. Milne and D.A. Waller
2013 Northeastern Naturalist Vol. 20, No. 3
(Fig. 1). Although this experimental setup presents some minor limitations (e.g.,
cotton-filled pitchers do not allow for spiders to reside within the pitchers, models
are not green like other treatments), the main morphological features are
effectively separated using this design. Five replicates of each of these treatments
(25 total) were created. Plants and models were modified so that each had five
pitchers. For live treatments, flower stalks were cut off early in development to
prevent flowering.
Each N-P+W+ had its peristome covered with a clear, quick-hardening sealant
(Lexel super-elastic sealant, Sashco Sealants, Inc.). In a preliminary study,
slices ≈1 mm thick were cut from the peristome of sealed pitchers and mounted
on a slide. Examination of slides under light microscopy at 20x revealed that this
sealant covered the stomata on the epidermal surface and therefore plugged any
other glands associated with nectar production.
To minimize the effect of variable prey availability, treatments were randomly
placed within a 100-m x 100-m area. This area was adjacent to naturally growing
pitcher plants and vegetation similar to areas at BEP where natural populations of
Purple Pitcher Plant grew. All plants were kept in pots (16.5 cm diameter x 18.4
cm depth) and placed into the soil so that the top of each pot was flush with the
ground. Leaf litter from adjacent areas was spread at the base of the plants and
the plant models so that it resembled the surrounding area. Manipulations of the
plants to create the different treatments were conducted on the first day of setup.
All treatments were watered every day of data collection. The area of pitcher
openings was measured and recorded twice during the study for all treatments
except N+P+W- because the opening was filled with cotton and therefore a spider
could not reside within it.
Figure 1. Treatments used in this study: A) N-P-W+, B) N+P+W+, C) N+P+W- (note
cotton in pitcher), D) N+P-W+, and E) N-P+W+ (arrow indicates coated peristome).
M.A. Milne and D.A. Waller
2013 Northeastern Naturalist Vol. 20, No. 3
422
Treatments were allowed to equilibrate in the surrounding area for one week
prior to data collection. After this time period, all spiders found walking on, inhabiting
a web directly over (less than ≈5 cm), inhabiting a web attached to, or inhabiting
a web inside the pitchers of all plants and models (henceforth termed “residents”)
were removed three times a week for four weeks and then once a week for a
month. The position (web over pitcher, web inside pitcher, or web against pitcher)
of residents was recorded, after which they were collected and preserved for
later identification. Residents were identified to species using Ubick et al. (2005)
and other taxonomic keys.
Differences in the total number of female and male, immature and mature,
or ground and web-building residents were each separately analyzed
via a Wilcoxon rank-sum test using SPSS (IBM SPSS Inc., SPSS Statistics
v. 20, Chicago, IL). Differences among treatments in the number of ground,
web-building, and total residents were each separately analyzed via a Kruskal
Wallis test in SPSS, as was the difference in the size of pitchers among
treatments. SPSS was also used to run Fisher’s exact tests to determine significant
differences between the number of adult and immature residents in
Linyphiinae and Erigoninae. Permutation chi-square tests were conducted
using SAS (SAS Institute, Inc., SAS v. 9.3, Cary, NC) to determine the difference
between adult and immature residents in the placement of their webs for
the erigonines, linyphiines, and total linyphiids.
Results
Eight families of spiders were found among 123 collected residents (Table 1).
Web-building residents were found significantly more often than ground-spider
residents (Wilcoxon test = 465.0, z = -3.41, P < 0.001; Fig. 2). However, there
was no significant difference among treatments in the number of ground (Kruskal
Wallis test: χ2 = 1.82, df = 4, P = 0.77) or web-building residents (Kruskal Wallis
test: χ2 = 1.77, df = 4, P = 0.78; Fig. 2). There was also no significant difference
among treatments in the total number of residents found (Kruskal Wallis test: χ2 =
2.09, df = 4, P = 0.72; Fig. 2).
Table 1. Total number of spider residents found for each family across all treatments
Taxon Number of residents found
Agelenidae 1
Araneidae 1
Dictynidae 1
Erigoninae (Linyphiidae) 27
Linyphiinae (Linyphiidae) 61
Lycosidae 8
Salticidae 11
Tetragnathidae 1
Theridiidae 3
Unknown immatures 9
423
M.A. Milne and D.A. Waller
2013 Northeastern Naturalist Vol. 20, No. 3
Approximately half of all of the spiders in webs were adults (49.5%), and the
other half were immature (50.5%). There was no significant difference among
all treatments between the number of female and male (Wilcoxon test = 590.0,
z = -0.95, P = 0.34; Fig. 3a) and between the number of mature and immature
(Wilcoxon test = 635.0, z = -0.05, P = 0.96; Fig. 3b) residents found.
The mean area of pitcher openings was 5.28 cm2 (n = 200; SE = 0.21). The
first measurement, taken during the early part of the study (mean = 5.14; n = 100;
SE = 0.29), only slightly differed from the second measurement, taken later (mean
= 5.41; n = 100; SE = 0.30). N-P-W+ had a significantly greater pitcher size than
the other treatments (Kruskal Wallis test: χ2 = 58.8, df = 3, P < 0.001): N+P-W+
(mean = 4.05; n = 50; SE = 0.23); N-P+W+ (mean = 3.48; n = 50; SE = 0.30);
N+P+W+ (mean = 3.94; n = 50; SE = 0.24); N-P-W+ (mean = 9.62; n = 50; SE = 0).
The most common residents were spiders in the sheet-web weaving family,
Linyphiidae. Due to the abundance of this family in our study, we concentrated
much of our analysis on their numbers. The most common linyphiids found were:
Agyneta morphospecies 1 (16), Ceratinopsis interpres Emerton (12), and Agyneta
morphospecies 2 (7) (Agyneta is a difficult genus to identify to species, so
specimens were separated into morphospecies). Linyphiids accounted for 83.5%
of the spiders in webs near the plant. Most linyphiid webs were built against the
pitcher as opposed to over or within the pitcher (Permutation test: χ2 = 11.46,
df = 2, P = 0.003; Fig. 4).
Figure 2. Number + SE of ground, web-building, and total spider residents found per
treatment type.
M.A. Milne and D.A. Waller
2013 Northeastern Naturalist Vol. 20, No. 3
424
Members of the linyphiid subfamily Linyphiinae were three times more abundant
as residents compared to members of the linyphiid subfamily Erigoninae. A
greater number of linyphiine residents were adults rather than immature (Fisher’s
Figure 3. (A) Total number of female and male resident spiders near pitchers per treatment
type; (B) Total number of mature and immature resident spiders near pitchers per
treatment type.
425
M.A. Milne and D.A. Waller
2013 Northeastern Naturalist Vol. 20, No. 3
exact test: P < 0.01; Fig. 4). However, there was no significant difference between
the residency rate of adult versus immature erigonines (Fisher’s exact test:
P = 0.82; Fig. 4). Linyphiines were more likely to build webs against the pitcher
than inside or over the pitchers (Permutation test: χ 2 = 14.45, df = 2, P < 0.001),
although this trend was non-significant in the erigonines (Permutation test: χ2 =
0.636, df = 2, P = 0.82; Fig. 4). All other residency comparisons between maturity
and web location were non-significant.
Discussion
This is the first study in which the morphological features of a carnivorous
plant were isolated in an attempt to determine their individual effects on spider
residency. Three conclusions may be inferred from these data: 1) the morphological
features of the Purple Pitcher Plant do not influence how often spiders
resided on or over the plant, 2) there was no significant differences in the sex
or maturity level among the spider residents over all treatments, and 3) spider
residents often build webs inside pitchers when regular web size is similar to
pitcher opening size.
The lack of difference among treatments in the density of residents found suggests
that spiders were non-selective for the presence of the tested Purple Pitcher
Plant features when choosing a living site. Spiders encountering the Purple Pitcher
Plant fell victim to the plants or built webs near them. They did not appear to
Figure 4. Total number of webs built by both linyphiid subfamilies over all treatments.
M.A. Milne and D.A. Waller
2013 Northeastern Naturalist Vol. 20, No. 3
426
seek out plants with high amounts of dead prey (Cresswell 1991, 1993) because
there was no preference for treatments that held dead prey versus the cotton-filled
pitchers that lacked prey. However, the lack of a significant difference among
our treatments in the rate of spider residency may have been a result of our low
sample size (only five replicates of each treatment type). Moreover, further studies
may be warranted to test if spider prey density near the Purple Pitcher Plant is
higher than spider prey density further from the plant, as a significant difference
may have also influenced the results.
Female spiders lead a largely sedentary lifestyle and are likely to be found in
webs, while adult males often wander, looking for females, and immature males
are largely confined to their webs or retreats (Foelix 2010). Therefore, adult
males are more likely to be resident wanderers, crawling on the plant, while females
and immature males are more likely to be sedentary residents. Although
there was no statistical difference between male and female residents, there was
a trend for females to be residents more often (Fig. 3). A sampling bias may
have affected these values; our sampling method may have been biased towards
web-builders because transient ground spiders were less likely to be found
within the short time the plants were checked.
The most common residents, linyphiids, are sheet-web weavers that build
sticky horizontal webs (Foelix 2010) based on the presence of vertical structures
for support (Halaj et al. 2000, Samu et al. 1996), which were most often against
Purple Pitcher Plant pitchers (Fig. 4). Linyphiids normally build webs at about
10 cm off the ground (Sunderland et al. 1986a), a height similar to that of Purple
Pitcher Plant pitchers. Therefore, it is possible that this association is coincidental.
More studies must be conducted to determine if more spiders reside near the
Purple Pitcher Plant as opposed to away from the plant.
Linyphiids may be divided into two main subfamilies: Erigoninae and
Linyphiinae. As adults, erigonine spiders commonly build webs about 3–8 cm2 in
area (Harwood et al. 2001, Sunderland et al. 1986b), a size range that corresponds
to the mean area inside the pitchers in our treatments (5.28 cm2). Therefore, the
insides of pitchers might seem like ideal web locations for adult erigonines, but
the slipperiness of the inner walls may have led to high death rates of these spiders,
lowering the number of adult erigonines found in webs inside pitchers in
this study. This hypothesis is supported by the high number of dead erigonines
found captured in the pitchers during this study (M.A. Milne, pers. observ.).
Similarly, linyphiines often choose web sites based on the presence of vertical
structures to support their webs (Halaj et al. 2000, Samu et al. 1996). Adult
linyphiines build webs from 16 cm2 (Sunderland et al. 1986b) to 74cm2 (Harwood
et al. 2001) in area and immatures build a smaller web (<16 cm2; Harwood et al.
2001). These mean web sizes, when compared to the mean area of the pitchers
used in this study, may explain why more immature linyphiines were found in
webs inside pitchers than adults (Fig. 4). Therefore, although there was a lack of
selection for residency near specific treatments due to differences in which morphological
features were present, there may have been a selection by erigonines
427
M.A. Milne and D.A. Waller
2013 Northeastern Naturalist Vol. 20, No. 3
and immature linyphiines for the interior pitcher size presented by the Purple
Pitcher Plant and models.
This study provides evidence for the hypothesis that spiders do not reside
near the Purple Pitcher Plant due to any unique morphological feature possessed
by the plant. Although it was hypothesized that the prey captured by the Purple
Pitcher Plant would attract spider scavengers, spider density was just as high near
plants that did not have captured prey. It is therefore possible that spiders treat
carnivorous plants as any other type of vegetation of that height. Moreover, further
experiments should test the hypothesis that spiders view the Purple Pitcher
Plant as competition and therefore avoid the plant, as has been seen with another
carnivorous plant, the Pink Sundew (Jennings et al. 2010).
Acknowledgments
The authors would like to thank Scott Richter for statistical help, Phil Sheridan for aiding
in planting the Sarracenia, Bill Scholl (an expert in custom wood and metalcraft) for
the creation of the pitcher plant models, Darren Loomis and the Virginia Department of
Conservation and Recreation, the American Arachnological Society for a student grant, and
two anonymous reviewers for helpful comments on an earlier version of this manuscript.
Literature Cited
Barnes, R.D. 1953. The ecological distribution of spiders in non-forest maritime communities
at Beaufort, North Carolina. Ecological Monographs 23:315–337.
Cresswell, J.E. 1991. Capture rates and composition of insect prey of the pitcher plant
Sarracenia purpurea. American Midland Naturalist 125:1–9.
Cresswell, J.E. 1993. The morphological correlates of prey capture and resource parasitism
in pitchers of the carnivorous plant Sarracenia purpurea. American Midland
Naturalist 129:35–41.
Di Giusto, B., V. Grosbois, E. Fargeas, D.J. Marshall, and L. Gaume. 2008. Contribution
of pitcher fragrance and fluid viscosity to high prey diversity in a Nepenthes carnivorous
plant from Borneo. Journal of Bioscience 33:121–136.
Duffey, E. 1966. Spider ecology and habitat structure. Senckenbergiana biologica
47:45–49.
Elliot, F.R. 1930. An ecological study of the spiders of the beech-maple forest. Ohio
Journal of Science 30:1–22.
Enders, F. 1977. Web-site selection by orb-web spiders, particularly Argiope aurantia
Lucas. Animal Behaviour 25:694.
Foelix, R.F. 2010. Biology of Spiders. Oxford University Press, New York, NY.
Frost, C., and L. Musselman. 1987. History and vegetation of the Blackwater Ecologic
Preserve. Castanea 52:16–46.
Green, M.L., and J.D. Horner. 2007. The relationship between prey capture and characteristics
of the carnivorous pitcher plant, Sarracenia alata Wood. American Midland
Naturalist 158:424–431.
Halaj, J., D.W. Ross, and A.R. Moldenke. 2000. Importance of habitat structure to the
arthropod food-web in Douglas-fir canopies. OIKOS 90:139–152.
Halley, J.M., C.F.G. Thomas, and P.C. Jepson. 1996. A model for the spatial dynamics of
Linyphiid spiders in farmland. The Journal of Applied Ecology 33:471–492.
M.A. Milne and D.A. Waller
2013 Northeastern Naturalist Vol. 20, No. 3
428
Harwood, J.D., K.D. Sunderland, and W.O.C. Symondson. 2001. Living where the food
is: Web location by linyphiid spiders in relation to prey availability in winter wheat.
Journal of Applied Ecology 38:88–99.
Heard, S.B. 1998. Capture rates of invertebrate prey by the pitcher plant, Sarracenia
purpurea L. American Midland Naturalist 139:79–89.
Hubbard, H.G. 1896. Some insects which braved the dangers of the pitcher-plant. Proceedings
of the Entomological Society of Washington 3:314–318.
Jennings, D.E., J.J. Krupa, T.R. Raffel, and J.R. Rohr. 2010. Evidence for competition
between carnivorous plants and spiders. Proceedings of the Royal Society B
277:3001–3008.
Joel, D.M. 1986. Glandular structures in carnivorous plants: Their role in mutual and unilateral
exploitation of insects. Pp. 219–234, In B. Juniper and R. Southwood (Eds.).
Insects and the Plant Surface. Edward Arnold, Baltimore, MD. 360 pp.
Joel, D.M., B.E. Juniper, and A. Dafni. 1985. Ultraviolet patterns in the traps of carnivorous
plants. New Phytologist 101:585–593.
Jones, F.M. 1935. Pitcher plants and their insect associates. Pp. 25–30, In M.V. Walcott
(Ed.). Illustrations of North American Pitcher Plants. Smithsonian Institution, Washington
DC. 34 pp.
Judd, W.W. 1959. Studies of the Byron bog in Southwestern Ontario X. Inquilines
and victims of the pitcher-plant Sarracenia purpurea L. Canadian Entomologist
91:171–180.
Juniper, B.E., R.J. Robins, and D.M. Joel. 1989. The Carnivorous Plants. Academic
Press, London, UK. 353 pp.
Kareiva, P., D.H. Morse, and J. Eccleston. 1989. Stochastic prey arrivals and crab spider
giving-up times: Simulations of spider performance using two simple “rules of
thumb”. Oecologia 78:542–549.
Lloyd, F.E. 1942. The Carnivorous Plants. The Ronald Press Company, NY. 380 pp.
Milne, M.A. 2012. The Purple Pitcher Plant as a spider oviposition site. Southeastern
Naturalist 11:567–574.
Muma, M.H., and K.E. Muma. 1949. Studies on a population of prairie spiders. Ecology
30:485–503.
Post, W.M., and S.E. Riechert. 1977. Initial investigation into the structure of spider communities.
The Journal of Animal Ecology 46:729–749.
Riechert, S.E. 1974. The pattern of local web distribution in a desert spider: Mechanisms
and seasonal variation. The Journal of Animal Ecology 43:733–746.
Riechert, S.E. 1985. Decisions in multiple goal contexts: Habitat selection of the spider,
Agelenopsis aperta (Gertsch). Zeitschrift fur Tierpsychologie 70:53–69.
Robinson, J.V. 1981. The effect of architectural variation in habitat on a spider community:
An experimental field study. Ecology 62:73–80.
Rymal, D.E., and G.W. Folkerts. 1982. Insects associated with pitcher plants (Sarracenia:
Sarraceniaceae), and their relationship to pitcher plant conservation: A review.
Journal of the Alabama Academy of Science 53:131–151.
Samu, F., K.D. Sunderland, C.J. Topping, and J.S. Fenlon. 1996. A spider population in
flux: Selection and abandonment of artificial web sites and the importance of intraspecific
interactions in Lepthyphantes tenuis (Araneae, Linyphiidae) in wheat. Oecologia
106:228–239.
Schnell, D.E. 2002. Carnivorous Plants of the United States and Canada. Timber Press,
Portland OR. 468 pp.
429
M.A. Milne and D.A. Waller
2013 Northeastern Naturalist Vol. 20, No. 3
Sheridan, P., J. Humphrey, M. Davies, C. Simon, and N. Penick. 2000. Comparison of
insect captures between wild-type and mutant green Sarracenia jonesii Wherry. Virginia
Journal of Science 51:129.
Sunderland, K.D., A.M. Fraser, and A.F.G. Dixon. 1986a. Field and laboratory studies of
money spiders (Linyphiidae) as predators of cereal aphids. Journal of Applied Ecology
23:433–477.
Sunderland, K.D., A.M. Fraser, and A.F.G. Dixon. 1986b. Distribution of linyphiid spiders
in relation to capture of prey in cereal fields. Pedobiolog ia 29:367–375.
Tanaka, K. 1991. Food consumption and diet composition of the web-building spider
Agelena limbata in two habitats. Oecologia 86:8–15.
Turnbull, A.L. 1964. The search for prey by a web-building spider Achaearanea tepidariorum
(C.L. Koch) (Araneae, Theridiidae). The Canadian Entomologist 96:568–579.
Ubick, D., P. Paquin, P.E. Cushing, and V. Roth (Eds.). 2005. Spiders of North America:
An Identification Manual. American Arachnological Society, http://www.americanarachnology.
org/. 377 pp.
Waldorf, E.S. 1976. Spider size, microhabitat selection, and use of food. American Midland
Naturalist 96:76–87.
Williams, S.E. 1976. Comparative sensory physiology of the Droseraceae: The evolution
of a plant sensory system. Proceedings of the American Philosophical Society
120:187–204.
Wray, D.L., and C.S. Brimley. 1943. The insect inquilines and victims of pitcher plants in
North Carolina. Annals of the Entomological Society of America 36:128–137.
Zamora, R. 1995. The trapping success of a carnivorous plant, Pinguicula vallisneriifolia:
The cumulative effects of availability, attraction, retention, and robbery of prey.
Oikos 73:309–322.