Current Biology 19, 740–744, May 12, 2009 ª2009 Elsevier Ltd All rights reservedDOI 10.1016/j.cub.2009.03.015
Communal Nutrition in Ants
Audrey Dussutour1,2,* and Stephen J. Simpson1
1School of Biological Sciences and Centre for Mathematical
The University of Sydney
2Centre de Recherches sur la Cognition Animale
UMR 5169 CNRS
Universite ´ Paul Sabatier
Studies on nonsocial insects have elucidated the regulatory
strategies employed to meet nutritional demands [1–3].
However, how social insects maintain the supply of an
appropriate balance of nutrients at both a collective and an
individual level remains unknown. Sociality complicates
nutritional regulatory strategies [4–6]. First, the food
entering a colony is collected by a small number of workers,
which need to adjust their harvesting strategy to the
demands for nutrients among individuals within the colony
[4–7]. Second, because carbohydrates are used by the
workers and proteins consumed by the larvae [7–14], nutri-
tional feedbacks emanating from both must exist and be
integrated to determine food exploitation by foragers [4–6,
15, 16]. Here, we show that foraging ants can solve nutri-
tional challenges for the colony by making intricate adjust-
ments to their feeding behavior and nutrient processing,
acting both as a collective mouth and gut. The amount and
balance of nutrients collected and the precision of regula-
tion depend on the presence of larvae in the colony. Ants
improved the macronutrient balance of collected foods by
extracting carbohydrates and ejecting proteins. Neverthe-
less, processing excess protein shortened life span—an
effect that was greatly ameliorated in the presence of larvae.
Results and Discussion
We first aimed to establish whether there is a ratioand a rate of
protein and carbohydrate collected that are maintained in the
face of variation in the nutritional environment. Accordingly,
20 colonies of green-headed ants, 10 with larvae present from
the start and 10 without, were challenged to demonstrate
whether they have the capacity to regulate intake of protein
and carbohydrate when offered a total of six different two-
food choices, varying in the ratio and concentration of protein
and carbohydrate. Achieving the same intake of protein and
carbohydrate in the face of six different complementary food
pairings would prove that ants have the capacity to regulate
both protein and carbohydrate collection. The choices were
(5) 2:1 versus 1:3 (200 g/l), and (6) 2:1 versus 1:3 (100 g/l).
Despite being provided with two different nutrient ratios and
a 3-fold range of nutrient concentrations, colonies with larvae
maintained the ratio and amounts of protein and carbohydrate
collected remarkably consistently (Figure 1 and Tables S1
and S2 available online). Nutrient intake differed in three
respects according to the presence of larvae. First, colonies
with larvae maintained a higher nutrient intake than colonies
without larvae, i.e., they ate more food. Second, the regulated
P:C ratio was more protein biased for colonies with larvae
than for those without larvae. Third, whereas colonies with
larvae were able to maintain nutrient intake constantly across
a 3-fold range of nutrient dilutions, the colonies without larvae
maintained nutrient intake when the diet was diluted from
300 to 200 g/l but were unable to do so when the foods were
the nutritional requirements of the colony but also contributes
to the effectiveness of nutritional regulation.
Having established that colonies are able to switch among
nutritionally imbalanced but complementary foods to maintain
the supply of protein and carbohydrate, a second experiment
explored the responses of colonies when confined to a single
diet containing an excess of one nutrient relative to the other.
In this experiment, the ants were forced to ingest foods that
were to some extent imbalanced and confront the situation
wherein there is conflict between meeting their requirements
for protein and carbohydrates. We confined 30 colonies with
larvae at the start and 30 colonies without larvae initially to
one of five diets varying in P:C (1:3, 1:2, 1:1, 2:1, and 3:1—all
at 200 g/l for P + C). Food collected was measured for each
colony over 2 day periods across 50 days. The resulting
nutrient collection arrays are shown in Figures 2A–2D and indi-
was higher for colonies with larvae initially than for colonies
without larvae (Figure 2 and Table S3). Second, colonies
without larvae from the beginning of the experiment collected
substantial excesses of protein when fed with the highest P:C
hydrate intake. The tendency for the array to run parallel to the
protein axis in Figure 2A indicates that all colonies managed to
collect almost the same quantity of carbohydrates regardless
of the diet that they were fed. Third, colonies with larvae
made greater efforts to maintain protein intake than did those
without larvae. Thus, on the lowest P:C diet (1:3), collection of
food increased to provide limiting protein (indicated by the
pronounced kink upward in the intake array relative to 1:2 in
Figure 2B), whereas, on the highest P:C diet (3:1), food collec-
tion was reduced (at least up until day 18), hence ameliorating
excess protein collection (shown by the kink downward in the
intake array relative to 2:1). Beyond day 18 on diet 3:1 and
day32on 2:1,alllarvaehaddied, indicating acosttothelarvae
of excess protein collection (see below), and thereafter, these
colonies assumed the intake pattern seen for colonies without
larvae, i.e., a large increase in food collection (see arrows on
In the course of the experiment, we noticed that ants were
storing food in the form of pellets inside the nest before
removing them from the nest and stockpiling them in a waste
dump. Consequently, ants were not eating all of the food that
they were harvesting. We collected, dried, and weighed the
pellets from the waste dump at the end of the experiment.
The number of stockpiled pellets increased as the ratio of
protein to carbohydrate in the diet increased, with little or no
waste being stockpiled on the lowest P:C diet (Figures 3, S1,
S3, and Table S4). In addition, the number of pellets on the
without larvae. The question arose as to whether the chemical
composition of the waste pellets differed from that of the food.
Extraordinarily, the chemical composition of the stockpiled
tion of protein increased in the diet, the proportion of protein in
the pellets rose much faster (Figure S2 and Table S5). The
concentration of carbohydrate was considerably lower in the
pellets than in the diet, whereas the quantity of protein was
increasingly higher in the stockpiled waste than in the food as
dietary P:C rose. Therefore, ants were manipulating the diet
collected, extracting the carbohydrates, and rejecting excess
protein in the form of pellets. The presence of larvae affected
the extent of this manipulation; in particular, colonies with
larvae were more effective in voiding excess collected protein
than colonies without larvae when supplied with protein-
biased diets (compare the shaded triangles in Figures 3A
When adjusted for this postcollection manipulation of diet
composition and ejection of unwanted food residues onto
the waste dump (nutrients collected minus nutrients rejected),
the intake array for colonies with larvae shifted, such that
estimated intake of protein varied less across the range of
dietary P:C values than did the array based on food collected
(Figure 3B). For protein-biased diets, colonies were still
supplied with an excess of protein, but not as large as the
excess predicted from the food collected. In colonies without
larvae from the outset, the corrected intake array was not
substantially changed relative to the array for collected nutri-
ents (Figure 3A). When the same adjustments for manipula-
tion of dietary composition were made to foods collected
during the choice experiment (Figure 1), the intake target
shifted to align with a ratio closer to 1:1.5 for colonies with
larvae but 1:2 for colonies without larvae (open red circles
in Figure 3).
Finally, we measured various performance indicators for the
colonies on different diets. Ant mortality increased substan-
tially at the two highest P:C ratios (2:1 and 3:1) (Figures 4A
and 4B and Table S6). Surprisingly, this pattern was consider-
ably less pronounced in the presence of larvae from the begin-
ning of the experiment. The number of larvae produced per
colony was also a function of dietary P:C. Colonies without
larvae at the beginning had produced the most larvae by
day 50 when confined to diet 1:2. Colonies with larvae present
from the beginning had a higher number of larvae at the end of
50 days than did colonies in which larvae were absent initially
(Figure 4C). Larvae introduced into the colony before the
beginning of the experiment died after 2–3 weeks when colo-
nies were fed with the most protein-biased diets but survived
andmetamorphosed incolonies fedwithcarbohydrate-biased
diets (Figure 4D).
tional state of the regulating entity. In the case of ants, the
assessment and collection of food is undertaken on behalf of
the colony by the foraging ants, which can be specialized in
collecting differentfood types . The major sink for collected
protein is growing larvae, whereas worker ants require mainly
carbohydrate for energy. Accordingly, when larvae were pre-
sent in the colony, ants not only collected more food in total,
foragers. More than this, however, if larvae were present, ants
regulated macronutrient intake more precisely when offered
choices of nutritionally complementary foods. Notably, in the
presence of larvae, ants compensated for a 3-fold change in
rate adjustments to the amount of food collected. However,
when larvae were absent from thebeginningof the experiment,
antsdidnot increasefood collectionon the most dilutedfoods.
Ina previous study, we showedthat, in the face of changes
in the concentration of sugar solution, ants were better able to
Figure 1. Protein and Carbohydrate Collection Measured during Choice
(A and B) Empty circles and crosses represent the amount of protein (P) and
carbohydrate (C) collected for each replicate for colonies without larvaeand
with larvae present from the outset of the experiment, respectively. Full
between the two foods in a food pairing treatment (dotted black lines). The
correspond to the two foods in a food pairing treatment. Note how colonies
with larvae converged upon the same point of nutrient collection in all treat-
ments. Colonies without larvae regulated nutrient collection to a lower P:C
ratio than did colonies with larvae, reflecting the increased protein needs
tion, indicating a role of larvae in colony nutrient regulation.
Three-way ANOVAs: choice effect on food collected and P:C ratio, F1,108=
0.38 (p = 0.534) and F1,108= 0.09 (p = 0.781); dilution effect on P:C ratio,
F2,108= 0.01 (p = 0.994); larval effect on P:C ratio and food collected, F1,108=
792.79 (p < 0.001) and F1,108= 939.12 (p < 0.001); dilution 3 larvae effect on
food collected, F2,108= 178.79 (p < 0.001).
Communal Nutrition in Ants
regulate their carbohydrate intake when larvae were present
rather than when larvae were absent.
Not only did ants regulate macronutrient collection more
precisely in the presence of larvae, but they also survived
better when fed high-protein diets. Excess protein ingestion
in relation to requirements has recently been shown to shorten
species that carbohydrates may be digested extraorally
because carbohydrase activity is present in salivary and
mandibular glands, whereas protein needs to be ingested
because protease activity is restricted to the midgut [21–23].
Figure 2. Cumulative Protein and Carbohydrates
Collected by Ants
Colonies were provided with one of five diets that
differed in their ratio of protein to carbohydrate
at 2 day intervals over 50 days (the results were
collection points are connected with lines to and
from collection arrays, which demonstrate the
nutrient balancing strategy. The inserted images
in (A) and (B) show examples of the amount of
by ants at 2 day intervals over 50 days is shown in
(C) and (D).
Four-way ANOVAs: time effect on the amount of
food collected, F24,960= 106.82 (p < 0.001); time 3
larvae effect, F24,960= 8.49 (p < 0.001); time 3 diet
effect, F96,960= 6.66 (p < 0.001); time 3 larvae 3
diet effect, F96,960= 3.14 (p < 0.001); larvae effect,
F1,40= 63.00 (p < 0.001); diet effect, F4,40= 17.48
(p < 0.001); larvae 3 diet effect, F4,40 = 0.60
(p = 0.661).
Figure 3. Protein and Carbohydrates Collected
and Ingested, i.e., Not Taken out and Placed on
a Waste Dump by Ants after 50 Days
differing in their ratio of protein to carbohydrate
over 50 days. Triangles show the amount of C
and P rejected from the food collected. Note
how colonies with larvae from the outset were
more effective than colonies without larvae in
manipulating the composition of collected food
by retaining the limiting nutrient and rejecting the
excess nutrient in collected food (shaded trian-
gles). The intake target collected is the amount
of carbohydrates and protein collected during
the choiceexperiment. The intaketargetingested
is the intake target once the correction for carbo-
hydrate extraction from the foods collected in the
choice experiments is made. Results are pre-
sented as intake per ant to adjust for mortality.
Three-way ANOVA: diet effect on the amount of stock, F4,40= 78.61 (p < 0.001); larvae effect, F1,40= 96.20 (p < 0.001). Four-way ANOVAs with repeated
measures: manipulation effect on C and P quantity in the stock, F1,40= 4068.94 (p < 0.001) and F1,40= 755.13 (p < 0.001); manipulation 3 larvae effect 3
diet effect on C quantity, F1,40= 8.45 (p < 0.001).
nest, followed by discarding unwanted
protein-rich food stock to an external
waste dump, resulted in ants improving
the macronutrient balance of collected
Why did ants discard more excess protein when larvae were
present from the outset than when they were absent? One
would expect that colonies without larvae, which do not
need as much protein, would have rejected a larger proportion
of excess collected protein on high-protein diets. Their failure
to do so indicates once again that the larvae are important in
providing nutritional feedbacks to workers. Workers, unlike
larvae, have a limited ability to digest bulky proteinaceous
foods in the midgut because of a combination of their narrow
waist (petiole) separating the thorax from the abdomen [7,
24, 25] and producing only very small amounts of proteases
in their midguts [22, 25]. Larvae, in contrast, are capable of
Current Biology Vol 19 No 9
protein digestion both extraorally through high protease levels
between workers and larvae explains why preys are fed to ant
larvae in an undigested state . Our results suggest that the
ants may further overcome the deleterious effects of excess
proteins by getting the larvae to process them, confirming
the hypothesis that larvae are not passive recipients of nutri-
tion but, rather, a protein digestive organ for the colony [4,
11, 27, 28].
Excess dietary protein, nevertheless, resulted in poor larval
performance (both survival and production). Ants that were
offered a choice of foods regulated their collection of macro-
nutrients to a ratio of protein to carbohydrate that appeared
to maximize neither ant life span nor larval survival and
production. However, once the correction for carbohydrate
extraction from the foods collected by the ants in the choice
and no-choice experiments is made, the macronutrient
balance shifts toward the protein-to-carbohydrate ratio that
best supported larval production andsustained maximallarval
for this partial misalignment between the ratio of nutrients
ingested and that which provided maximum performance
under no-choice conditions is unclear but is likely to relate to
the fact that the choice data were collected during a shorter
period (2 day periods for each of 6 diet pairings) than were
the performance results (50 days), and the target protein-to-
carbohydrate ratio may well have changed over time.
A striking division of labor has occurred in ants regarding
nutritional regulation. First, the foragers, responding to the
relationship between colony needs andthe nutritional environ-
Second, protein in the preprocessed food is digested by the
larvae, used for larval growth, and presumably fed back to
sustain the protein requirements of workers [4, 7, 27]. There-
after, residual excess protein is removed from the colony
and dumped. The nutritional interdependence among the
different actors within the colony is fully consistent with the
proposed importance of nutrition in the maintenance of
Figure 4. Colony Performance
Ants were provided with one of five diets differing
in their ratio of protein to carbohydrate over
(A and B) Mortality for colonies with and without
larvae from the beginning of the experiment.
(C) Number of larvae produced after 50 days.
(D) Number of larvae that hatched after 50 days in
beginning of the experiment.
Three-way ANOVAs: diet effect on the number of
dead ants, F4,40= 25.99 (p < 0.001); larvae 3 diet
effect, F4,40= 1.28 (p = 0.292); larvae effect, F1,40=
2.29 (p = 0.076); larvae effect, F1,40= 11.56 (p =
0.002). One-way ANOVA: diet effect on number
of ants that hatched, F4,29= 82.81 (p < 0.001).
sociality, in caste determination, and in
the initial evolution of sociality [29–31].
More broadly, our results provide an
example of how nutrient-specific inter-
actions between individuals can lead to
complex collective behaviors, just as
they can explain collective behavior in simpler group living
Full details of the Experimental Procedures are provided in the Supple-
mental Experimental Procedures.
Colonies of monomorphic green-headed ants (Rhytidoponera sp.)  were
collected in Sydney, Australia.
Choice Diet Experiment
nests [18, Supplementary Data]. Before starting the experiment, we added
100larvaeto10colonies.Weprepared12foods varying inboththe P:Cratio
following food choices, presented in random order at 2 day intervals: 3:1
1:3 (300 g/l), 2:1 versus 1:3 (200 g/l), and 2:1 versus 1:3 (100 g/l). Diet
consumption was measured as described below.
No-Choice Diet Experiment
imental nests . Before beginning the experiment, we added 60 larvae to
30 colonies. We prepared five diets differing in their content of protein (P)
and carbohydrates (C) . The 5 P:C ratios used were 3:1, 2:1, 1:1, 1:2,
and 1:3. The total concentration of protein and carbohydrates (P + C) was
200 g/l. Every 2 days for 50 days, 6 colonies with larvae and 6 colonies
without received 8 mg of one of the 5 diets in a Petri dish. The Petri dish
was weighed every 2 days before it was placed in the foraging arena and
again after it was removed. The quantities of carbohydrates and protein
were measured for each colony with the Phenol-sulphuric assay and the
Bradford assay, respectively. The number of larvae was estimated every
week and measured accurately after 50 days. The number of dead ants
within each colony was counted every 2 days, and corpses were removed.
Supplemental Data include Supplemental Experimental Procedures, three
figures, and seven tables and can be found with this article online at http://
Communal Nutrition in Ants
A.D. was supported by a postdoctoral grant from The University of Sydney.
for helping us collect ants and N. Soran and F. Clissold for helping us with
the chemical analysis. We also thank D. Rubenstein for his comments on
Received: January 9, 2009
Revised: February 12, 2009
Accepted: March 2, 2009
Published online: April 2, 2009
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