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2012 SOUTHEASTERN NATURALIST 11(4):567–574
The Purple Pitcher Plant as a Spider Oviposition Site
Marc A. Milne*
Abstract - Spiders’ nesting sites may vary depending on species-specific requirements
and environmental conditions. I report on the use of leaves of Sarracenia purpurea
(Purple Pitcher Plant) as oviposition sites by 5 species of spiders in Virginia and North
Carolina. The presence of egg sacs, webbing, and a protective female spider inside the
pitchers confirmed the spiders’ use of the carnivorous plant trap as a safe and secure nest
rather than a deadly mechanism by which many spiders have commonly become victims.
I also collected spiders in the surrounding environment to dete rmine if this microhabitat
is used by uncommon species or ones that are often found nearby. Almost all spiders
found within pitchers of S. purpurea were also found in the surrounding environment, but
not at high densities near S. purpurea. The decaying pitchers of S. purpurea may create
an ideal home for many spider species in environments where suitable oviposition sites
are hard to come by.
Spiders employ a range of behaviors to protect their egg sacs. Some place
them in webs or silk-lined tunnels, under stones or bark, or in rolled-up leaves;
others grasp them with their chelicerae or attach them to their own abdomens
(Foelix 2010). Silk sacs surround the eggs to help prevent water loss, desiccation,
and changes in temperature and humidity (Opell 1984). Although the egg
sac’s silk also aids in defense against predatory or parasitic organisms, adults of
certain species often take up residency near the egg sac in order to further aid in
the survival of the juveniles or eggs (Foelix 2010). Maternal care for the egg sac
among spider species ranges from abandonment to guarding and aiding in freeing
the eclosing spiderlings from the egg sac (Foelix 2010).
The carnivorous Sarracenia purpurea L. (Purple Pitcher Plant) is a low-lying
herbaceous plant that uses water-filled pitcher-shaped leaves to trap, kill, and
digest arthropod prey (Schnell 2002). Sarracenia purpurea thrives in sunny bogs
and marshes along the Gulf Coast, North on the Atlantic edge of North America
and West across Southern Canada, the largest range of any North American
carnivorous plant (Schnell 2002). Pitchers catch the most prey during the first
two weeks of opening (Fish and Hall 1978), yet pitchers persist during the full
growing season, often in a slowly senescing state whereby the pitcher leaf decays
from the top down over the course of the year (Schnell 2002). Many spiders have
been shown to associate with carnivorous plants, usually as either kleptoparasites
(Anderson and Midgley 2002; Cresswell 1991, 1993; Rymal and Folkerts 1982;
Schnell 2002) or victims (Heard 1998, Judd 1959, Wray and Brimley 1943).
Flying insects regularly oviposit in the liquid of S. purpurea pitchers, helping
to create a phytotelmatous community. However, the only known organism
that commonly utilizes an entire dry pitcher as its home is Exyra rolandiana
*University of North Carolina, Greensboro, NC 27412; mamilne@unc g.edu.
568 Southeastern Naturalist Vol. 11, No. 4
Grote (Noctuidae) (Pitcher Plant Moth), which spins egg sacs inside first-year
pitchers and feeds on the pitcher tissue (Schnell 2002), thus demonstrating a
parasitic-like relationship (Schnell 2002), while the plant’s relationship with
the macroinvertebrate phytotelmatous community has been shown to be at least
partially mutualistic (Bradshaw and Creelman 1984, Heard 1994, Mouquet et
al. 2008). For spiders, the use of S. purpurea pitchers as oviposition sites has
previously been noted for only one family of spiders (Lycosidae, as a refuge
for a spider with an egg sac) (Hubbard 1896, Jones 1935). Similarly, Rymal
and Folkerts (1982) note a relationship between spiders and an unspecified
Sarracenia species. The goal of my study was to determine which spider taxa
commonly build webs inside S. purpurea pitchers in the mid-eastern United
States, if these spiders select for specific states of senescence in the pitchers
when choosing their web location, and if these spiders were also commonly
abundant in the surrounding environment.
The Highlands Botanical Station (HBS; 35.05°N, 83.19°W) in Highlands, NC
(Macon County) and the Joseph Pines Preserve (JPP; 37.05°N, 77.24°W) near
Waverly, VA (Sussex County) were searched for spiders residing in S. purpurea
pitchers. HBS was sampled once a week through 8 weeks in June and July 2007,
and JPP was sampled once a month for 6 months from April–September 2008.
The sampled area at HBS is a marshy area on the outskirts of an 11-acre garden,
containing approximately 700 S. purpurea rosettes (consisting of approximately
16,554 pitchers when counted in late June) along a lake edge. The Joseph Pines
Preserve is an artificially managed, periodically burned, 100-acre site that contains
approximately 32 S. purpurea rosettes (consisting of approximately 1100
pitchers when counted in mid-September).
During each sampling period, all pitcher plants at the preserve were checked
for spider residents with egg sacs. Checking for spider residency consisted of examining
the insides of each pitcher on a plant for living spiders with egg sac(s).
When spiders were found, they were collected and preserved for later identification.
The number of egg sacs present with each spider was counted. The level of
senescence for each resided pitcher was determined through observation as either
“no senescence”, “partial senescence”, or “complete senescence”. Senesced
pitchers are from the previous growing season, begin their decay from the distal
portion of the leaf, and often lack the presence of water due to holes ripped in the
To estimate the abundance of spiders in the surrounding environment, ten
25-m2 square plots were created: 2 plots were placed within the pitcher plant
population (henceforth, “pitcher plant plots”) and 2 were adjacent to the population
(henceforth, “non-pitcher plant plots”) at HBS, while there were 3 plots of
each kind created at JPP. Each plot was sampled for spiders using 3 methods:
sweep netting, shrub beating, and pitfall trapping. Each technique was conducted
4 times over 2 months at HBS, and pitfall trapping was conducted once a month
over 6 months while sweep netting was done once every other month at JPP
(shrub beating was not conducted at JPP due to the lack of lar ge bushes).
2012 M.A. Milne 569
Sweep netting consisted of waving a sweep net (0.5 m diameter) over grassy
vegetation. The entire plot was sweep netted unless vegetation was too large.
Large vegetation (height > 0.25 m; stem width < 3 cm diameter) was sampled via
a beating sheet (shrub beating; 71 cm2). Plants that had a stem width larger than
3 cm in diameter were considered “trees”, and their foliage was not sampled.
Pitfall trapping consisted of using 147.9-ml (5-oz) cups filled half-full with soapy
water. Each pitfall trap was placed in the ground, flush with the forest floor. Five
pitfall traps were placed in each plot. Four of the 5 pitfall traps were placed at
approximately 1 m from each corner of the plot while the fifth pitfall trap was
placed at the center of each plot. After 1 week, the pitfall traps were collected
and the spiders preserved. All spiders were identified to species using Ubick et
al. (2005) and associated taxonomic keys.
Data were tested for normality and homogeneity of variance. If data did not
conform to these assumptions, then they were transformed. Comparisons of
diversity between pitcher plant and non-pitcher plant plots at each location were
done using independent t-tests.
Figure 1. Adult female Enoplognatha caricis living inside a senesced pitcher of S. purpurea
with 4 egg sacs (c).
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Twelve Enoplognatha caricis Fickert (Fig. 1), 8 Pirata insularis Emerton,
2 Theridion frondeum Hentz (Cobweb Weaver), 1 Eperigone maculata Banks,
and 1 Clubiona rhododendri Barrows adult females were observed with egg
sacs inside S. purpurea pitchers at HBS, while 1 adult female Rabidosa rabida
Walckenaer (Rabid Wolf Spider; Fig. 2) was observed with an egg sac residing in
Figure 2. Adult female Rabidosa rabida living inside a partially senesced pitcher of S.
2012 M.A. Milne 571
a pitcher at JPP. The number of egg sacs held by each spider varied by taxa; the
number of egg sacs held by E. caricis ranged from 1–5 (mean = 1.5, SD = 1.17,
mode = 1), and the E. maculata was seen with 3 egg sacs, while all other spider
types were seen with only 1 egg sac each (Table 1). All spiders were observed to
be residents of the pitchers as opposed to victims, as webbing spanned the inner
aperture of the pitchers, seeming to prevent the spiders’ capture and allowing
them to move freely around and out of the leaf. All spiders were found inside
partially or fully senesced pitchers.
Seven-hundred and sixty-nine spiders in 18 families were found in the
surrounding environment: 345 at HBS and 424 at JPP (Table 2). The most
common species found among both locations were P. insularis (110), T. frondeum
(24), Bathyphantes pallidus Banks (14), Pelegrina galathea Walckenaer
(10), and C. rhododendri (9). The species found with an egg sac in a pitcher
Table 1. Total numbers of spiders by species found with egg sacs in pitch ers.
Species # in pitchers with egg sacs Mean number of egg sacs
Clubiona rhododendri 1 1.0
Enoplognatha caricis 12 1.5
Eperigone maculata 1 3.0
Pirata insularis 8 1.0
Theridion frondeum 2 1.0
Rabidosa rabida 1 1.0
Table 2. Total numbers of spiders by family found in pitcher plant (PP) vs. non-pitcher plant
Family NPP PP NPP PP
Agelenidae 0 0 1 0
Araneidae 6 14 21 15
Atypidae 0 0 0 1
Clubionidae 17 1 1 0
Corinnidae 0 0 0 2
Dictynidae 0 1 1 0
Gnaphosidae 0 0 3 7
Hahniidae 0 0 4 4
Linyphiidae 50 36 21 31
Lycosidae 95 13 61 52
Miturgidae 0 0 1 0
Oxyopidae 2 1 13 5
Philodromidae 0 0 3 0
Pisauridae 4 2 12 10
Salticidae 5 23 49 68
Theridiidae 41 14 2 2
Thomisidae 5 6 11 18
Unknown 2 7 2 3
Total 227 118 206 218
572 Southeastern Naturalist Vol. 11, No. 4
at JPP (R. rabida) was also found in the non-pitcher plant plots (3), but not in
the pitcher plant plots. At HBS, C. rhododendri (9) and E. maculata (1) were
found in non-pitcher plant plots but not in pitcher plant plots, E. caricis was
not found within either plot type, and P. insularis and T. frondeum were found
in both plot types. However, P. insularis and T. frondeum were found at much
higher densities in the non-pitcher plant plots than in the pitcher plant plots
(n = 78 for P. insularis in non-pitcher plant plots, and n = 9 in pitcher plant
plots; n = 22 for T. frondeum in non-pitcher plant plots, and n = 2 in pitcher
plant plots). There was no significant difference in the diversity of spiders between
pitcher plant and non-pitcher plant plots at HBS (t = 0.95, df = 34, P =
0.35) or JPP (t = 0.91, df = 34, P = 0.11).
Spiders are prone to capture by S. purpurea (Heard 1998, Judd 1959, Wray
and Brimley 1943). Therefore, if spiders were to build webs in actively trapping
pitchers, they must first prevent capture and make the pitcher s afe for residency.
This precaution may be why the spiders observed in this study resided in senesced
pitchers—pitchers that no longer posed a significant threat to arthropods
(Fish and Hall 1978). Because these older, senesced leaves no longer function for
prey capture, the plant is unlikely to be at a disadvantage by housing such spider
residents, making the relationship most likely a commensalism, though more
quantification should be done to confirm this hypothesis.
The abundance of each species found in both locations varied from very
abundant (P. insularis) to a single representative (E. maculata). However, these
numbers should be considered underestimates because the many immatures that
were found could not be identified to species (fully developed reproductive parts
are usually required to identify spiders to species). The diversity and abundance
of spiders with egg sacs found in pitchers was much lower than that which was
found in the environment at both locations (Tables 1, 2). Almost all spiders that
had egg sacs in pitchers were also found in the environment, but were either absent
or at low densities within plots that held pitcher plants. These differences in
density could have been due to differences in other vegetation types and amounts
between pitcher plant and non-pitcher plant plots, which would affect the density
of spiders. However, these differences may also indicate a preference by some
spider species for habitat without pitcher plants or, perhaps, that these species are
frequently captured by pitcher plants and are therefore at low densities nearby.
Since all of the species that were found with egg sacs in pitchers were either
absent or at low densities near pitcher plants, the leaves of S. purpurea may be a
specific microhabitat that is preferentially utilized by these species for oviposition.
More quantification should be done to determine the cause of this variability
in spider density.
Only a few scattered reports exist of spiders using carnivorous plants as
oviposition sites (Hubbard 1896, Jones 1935, Rymal and Folkerts 1982). Spiders
residing in S. purpurea may gain an advantage over spiders using other
2012 M.A. Milne 573
microenvironments to raise their young. Pitchers are protected on multiple sides
by the inner leaf surface. These leaves may present a microenvironment similar to
the funnel webs of Agelenopsis or Sosippus, which are covered laterally by webbing
and have a rear retreat (Brady 1962, Foelix 2010). Interestingly, spiders of the
genus Agenelopsis build funnel-webs that funnel into S. purpurea pitchers and often
retreat to the bottom of the pitcher when disturbed (M.A. Milne, pers. observ.).
Moreover, S. purpurea pitchers may present an architectural “jackpot” for spiders
seeking shelter from predators or protection for their young. This advantage may
be particularly useful in bog habitats where protective vegetation is scarce.
I would like to thank Deborah Waller for her advice, James Costa for allowing me to
sample at the Highlands Biological Station, Phil Sheridan for allowing me to sample on
the Joseph Pines Preserve, the American Arachnological Society for a student grant, and
the Highlands Biological Station for the Martina Wadewitz Haggard grant.
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