Feeding habits of the European pond terrapin Emys orbicularis
in Camargue (Rhône delta, Southern France)
Dario Ottonello1,2, Sebastiano Salvidio2, Elisabeth Rosecchi1
The diet of the European pond terrapin Emys
orbicularis is poorly known, especially in the
Mediterranean region. Bannikov (1951) showed
that in the Russian Republic of Daghestan this
species mainly feeds on aquatic and terrestrial
invertebrates. Lebboroni and Chelazzi (1991) in
Tuscany (Italy), and Kotenko (2000) in Ukraine
noticed the predominance of invertebrates but
a high occurrence of plant matter in the diet.
The aim of our study was to determine the diet
of E. orbicularis in Camargue, a Mediterranean
habitat, and to investigate for eventual dietary
Emys orbicularis is widespread in Camargue (Rhône river
delta, southern France), an area where one of the two major
populations of the French Mediterranean region is found
(Cheylan, 1998). The diet of E. orbicularis in the Tour du
Valat estate, Camargue (43◦30N-4◦39E), was studied from
April to August 2003. In this region E. orbicularis is mainly
found in two kinds of habitats: manmade irrigation canals
and natural temporary marshes. During the study period,
water levels in marshes were highest in April (55 cm), while
drought occurred from the end of June until October.
In this study E. orbicularis specimens were collected in
all habitats independently from the season, but at the end of
June, the marshes dried out making it impossible to sample
terrapins in this habitat. European pond terrapins were cap-
tured preferentially by hands. Fyke nets, baited with beef,
were also used occasionally. In these cases nets were vis-
ited every hour to prevent the terrapins from eating other
trapped animals. Date of capture, sex, carapace length (CL)
1 - Station Biologique de la Tour du Valat, Le Sambuc
13200 Arles, France
Corresponding author; address: DIP.TE.RIS. Università
di Genova, Corso Europa 26, 16132 Genova, Italy
2 - DIP.TE.RIS. Università di Genova, Corso Europa 26,
16132 Genova, Italy
and habitat type were recorded on each capture, and only
specimens with evident sexual characters were considered
as adults (Lanza, 1983). All captured specimens were indi-
vidually marked by unique notch patterns on their carapace
and were held in separate buckets ﬁlled with shallow wa-
ter for 24 hours. The faecal samples collected were gently
washed with water and ﬁltered with a 500-micrometer sieve,
stored in 70% alcohol and examined under a dissecting mi-
croscope. Prey items were identiﬁed down to the lowest pos-
sible systematic level, depending on their digestion state,
using aquatic macroinvertebrate keys and a reference collec-
tion. For each food type, the number of items and their wet
weight were recorded. Prey items were grouped into major
taxa for statistical analyses. Faecal samples from recaptured
animals were excluded from the analysis. Two periods could
be distinguished within the sampling season: the reproduc-
tive phase (from the end of April to the middle of July) and
the post-reproductive phase (from middle of July to the end
Dietary composition was evaluated using three different
frequency of occurrence of food item x,
where Nxis the number of faecal samples with food item x
and Nis the total number of faecal samples,
percentage abundance by number of food item x,
where Txis the number of prey xof each faecal sample and
Ttis the total number of prey items of all faeces samples,
percentage abundance by weight of food item x,
where Yxis the weight of prey xof each faecal sample and
Ytis the total weight of prey items of all faeces samples.
This index was only used to compare an eventual shift in
consumption of plant matter.
Plant remains and unidentiﬁed matter were not consid-
ered in the percentage abundance analysis because they did
not occur as discrete units. The number of molluscs was
probably underestimated because shell fragments were con-
sidered as a single food item. Vertebrata remains only refer
©Koninklijke Brill NV, Leiden, 2005. Amphibia-Reptilia 26 (2005): 562-565
Also available online - www.brill.nl
Short Notes 563
to bone fragments, and very few ﬁsh scales found were con-
sidered as incidentally ingested.
During this study faeces from 31 terrap-
ins were obtained: twenty-one females (mean
CL =164.3 mm; range 143.5-190.0 mm), six
males (mean CL =139.2 mm; range 118.5-
155.0 mm) and four juveniles (mean CL =
74.4 mm; range 67.0-90.6 mm). Because of the
small size of faecal samples of males and ju-
veniles, a statistical comparison between sexes
and between adults and juveniles was not possi-
In terms of frequency of occurrence E. orbic-
ularis mainly fed on aquatic invertebrates, such
as Coleoptera, Decapoda, Odonata, Gastropoda
and Heteroptera (table 1). The most frequent
prey of adults was the introduced red swamp
crayﬁsh Procambarus clarkii that was absent
from juvenile samples (table 1).
Plant remains were present in 89% of adult
and 25% of juvenile faeces. Terrestrial or ﬂy-
ing invertebrates (adult Libellulidae and Coena-
grionidae, Araneae and Formicidae), were also
important, occurring in about 45% of samples
and representing 61% of the number of prey
items of juveniles and 9% of prey items of
adults. Terrestrial arthropods were more abun-
dant in the diet of adult specimens from canals
than in those from marshes (χ2=24.437;
DF =1; p<0.001), and the weight of plant
matter was higher in the faeces of adult ter-
rapins from canals, than in those from marshes
(χ2=24.545; DF =1; p<0.001).
The consumption of plant matter was also dif-
ferent between reproductive and post-reproduc-
tive period (χ2=19.195; DF =1; p<0.001)
but, considering only canals, we did not no-
tice differences between samples collected in
these two periods (χ2=1.3931; DF =1;
Our study showed that the European pond
terrapin is an opportunistic predator with a
broad dietary niche that could, as in many other
freshwater terrapins (Clark and Gibbons, 1969;
Georges, 1982; Chessman, 1986), vary from
carnivorous to omnivorous depending on habi-
tat, ontogenic stage or other factors. Indeed
in Camargue, faeces of juvenile E. orbicularis
were for the majority composed by animal re-
mains, whereas those of adults contained large
quantity of plant matter. These results must
be interpreted with precaution, given the small
sample size, but are consistent with those from
Tuscany, Central Italy (Lebboroni and Chelazzi,
1991). It is often difﬁcult to determine whether
plant matter is ingested incidentally with ani-
mal prey or is a primary food item (Lindeman,
1996). However, its relatively high frequency
of occurrence and percentage of abundance by
weight in adult samples allow us to consider that
plant matter was intentionally ingested.
In spring, adult terrapins inhabit principally
freshwater marshes, and it is likely that the
higher productivity of these temporary habitats,
compared to that of permanent waters (Swason
and Meyer, 1977; Danell and Sjoberg, 1982;
Crome 1986), combined with the absence of ﬁsh
competition for trophic resources, offer to ter-
rapins the best environment to carry out their
activity patterns (i.e. feeding, mating, basking
and ﬂoating). Our study showed that terrapins
were principally carnivorous during this period,
and that they ingested plant matter incidentally.
When temporary marshes dry out, generally at
the end of June, terrapins can undergo aesti-
vation, as observed in Dordogne by Naulleau
(1991), or move to irrigation canals as observed
on Tour du Valat estate (Olivier unpublished
data). Starting from this period until August
the consumption of plant matter (i.e. algae and
macrophyta) and also terrestrial invertebrates
increased. This phenomenon was already ob-
served by Clark and Gibbons (1969) in juveniles
of another Emydidae, Trachemys scripta.They
proposed different factors that may explain the
increase of plant consumption: a greater difﬁ-
culty in obtaining insects later in the season,
a decreased abundance of insects, or the sat-
isfaction of nutritional requirements with plant
matter. Our results suggest that E. orbicularis
shifts its diet from carnivorous to omnivorous
depending on different habitat uses probably
564 Short Notes
Tab l e 1 . Percentage of abundance by number (%A) and frequency of occurrence (%F) of prey items in faecal samples of
Emys orbicularis:Ad=adult, L =larvae.
Adults Juveniles Adults Juveniles
MOLLUSCA Tot. 18.7 12.5 37.0 25.0
Gastropoda 18.7 12.5 37.0 25.0
Bithyniidae (Bithynia sp.) Ad 2.3 0.0 11.1 0.0
Lymnaeidae (Galba sp.) Ad 4.1 0.0 7.4 0.0
Physidae (Physella sp.) Ad 9.6 9.4 25.9 25.0
Planorbidae Ad 2.3 3.1 7.4 25.0
Undetermined remains Ad 0.4 0.0 7.4 0.0
ARACHNIDA Tot. 1.0 3.1 7.4 25.0
Acarina Ad 0.5 0.0 3.7 0.0
Araneae Ad 0.5 3.1 3.7 25.0
CRUSTACEA Tot 14.1 0.0 66.7 0.0
Conchostraca Ad 6.3 0.0 11.1 0.0
Decapoda Cambaridae Ad 7.8 0.0 66.7 0.0
INSECTA Tot 65.7 84.4 88.9 100.0
Coleoptera 40.2 25.0 55.6 25.0
Dytiscidae L 4.1 0.0 7.4 0.0
Dytiscidae Ad 12.8 18.7 44.4 25.0
Hydrophilidae L 4.1 0.0 11.1 0.0
Hydrophilidae (Berosus sp.) Ad 18.7 6.3 22.2 25.0
Noteridae Ad 0.5 0.0 3.7 0.0
Diptera 0.9 0.0 7.4 0.0
Chironomidae L 0.5 0.0 3.7 0.0
Unidentiﬁed Ad 0.4 0.0 3.7 0.0
Heteroptera 15.0 3.0 25.9 25.0
Corixidae (Corixa sp.) Ad 13.7 0.0 14.8 0.0
Notonectidae (Notonecta sp.) Ad 0.9 3.0 11.1 25.0
Pleidae (Plea sp.) Ad 0.4 0.0 3.7 0.0
Hymenoptera Formicidae Ad 3.2 31.3 11.1 75.0
Odonata 5.0 18.8 37.0 50.0
Aeshnidae L 1.4 0.0 11.1 0.0
Coenagrionidae Ad 1.4 15.7 14.8 50.0
Libellulidae L 0.4 0.0 3.7 0.0
Libellulidae Ad 1.8 3.1 11.1 25.0
Trichoptera L 0.5 0.0 3.7 0.0
Unidentiﬁed Insecta 0.9 6.3 7.4 50.0
VERTEBRATA Undetermined remains 0.5 0.0 3.7 0.0
PLANT Undetermined remains – – – 88.9 25.0
Unidentiﬁed organic matter – – – 25.9 75.0
linked to differences in prey availability.Further
investigation and more data are needed to test
our hypothesis and to explain whether dietary
shifts of E. orbicularis in Camargue are linked
to different seasonal nutritional requirements, to
different habitat uses, or to differences in prey
availability. Vertebrate prey were rare in the fae-
ces, although amphibian larvae were regularly
observed during our sampling campaign, espe-
cially in freshwater marshes (Ottonello pers.
obs). Tadpoles and eggs could be preyed upon
by terrapins, as observed in northern Europe
(Skibinski, 1954), but would go undetected in
faeces due to complete digestion (Demuth and
Another important ﬁnding is that the exotic
red swamp crayﬁsh Procambarus clarkii was
the most frequent prey at the study site. In-
Short Notes 565
deed, pond terrapins actively preyed on live
crayﬁsh, as some terrapins were observed eating
red swamp crayﬁsh in the wild (Ottonello pers.
obs.). This result may be explained by the recent
proliferation of this crustacean in most freshwa-
ter habitats of Camargue (Rosecchi et al., 1998).
This introduced crayﬁsh is now food of many
birds, mammals and ﬁsh in different parts of Eu-
rope according to Geiger et al. (2005), who did
not quote any reptile. Therefore our study ads a
new species to their list of vertebrate predators.
Several methods have been suggested to con-
trol P. clarkii, as this invasive species is consid-
ered as a plague, in particular in Mediterranean
wetlands (Gutierrez-Yurrita and Montes, 1999;
Gherardi and Holdich, 1999). Our study sug-
gests that at least in Camargue, this alien species
could be limited by the natural predation ex-
erted by Emys orbicularis, a threatened native
Acknowledgements. This study was supported by the
Sansouire Foundation (Biological Station “Tour du Valat”)
and by the European ﬁnancial contribution “Leonardo Da
Vinci II” awarded by Commett Li.Sa. to Dario Ottonello.
We are grateful to Jean Oison and Anthony Olivier for their
help during sampling.
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Received: September 4, 2004. Accepted: December 18,