THE ENERGY BUDGET OF AN ORB WEB-BUILDING SPIDER
Comp. Biochem, Physiol

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Comp. Biochem, Physiol„ 1976, Vol, 54A, pp, 187 to 190. Peryamon Press. Printed In Great Britain
THE ENERGY BUDGET OF AN ORB
WEB-BUILDING SPIDER
David B. Peakall1 and Peter N. Witt2
1 Section of Ecology and Systematics, Cornell University, Ithaca, NY 14853 and
2 Division of Research, North Carolina Department of Mental Health, Raleigh, NC 27611, U.S.A.
(Received 22 July 1975)
Abstract—!. First measurements of increased total oxygen consumption of web-building Araneus diade-
matus spiders over resting animals are reported for nine webs of an adult female.
2.    Analysis of movie pictures and web photographs results in an estimate of the number of steps
and the amount of up and down movement which the animal used in construction of a single web.
3.    Combination of both measures permits calculation of step energy, which can be added to the
chemical energy involved in silk recycling, to lead to an appraisal of advantages and disadvantages
involved in the daily construction of individual orb webs by single animals.
4.    This is compared to data from the literature on the web-building strategies of other spiders.
INTRODUCTION
Orb-web building spiders have developed a highly
specialized strategy for survival: Long periods of im-
mobility alternate with a relatively short burst of ac-
tivity, when a web is constructed or a fly caught and
wrapped in the web. All this is made possible through
maximum use of silk: everywhere the animal moves
it lays a silken thread, it catches the prey in a silken
web and then wraps it in a silken bag. Each web
is built and used by one animal alone.
One way of assessing the relative advantages of
single trap building is to calculate the energy cost
of the spider’s activities. Silk has to be produced, its
quantity and turnover can be measured and the
resulting figures can be added to those expended in
movements used to lay down the silken thread. Web-
measurements on photographs have been found to
be such a convenient and accurate record of the
builder’s movements, that they have been extensively
used to gauge changes in behaviour caused by stress
factors in the environment (Witt, et al, 1968; Witt,
1971a). In this paper we evaluate the photographic
record of the Araneus diadematus (Glerck) web
together with movies of web construction to deter-
mine the number of steps which were necessary for
trap construction. A combination of oxygen con-
sumption measurements in spiders with movement
data permits us to assess the daily energy costs of
a web-building spider’s activity.
Our data can be compared to those obtained by
other authors (i.e. Edgar, 1971) for wolf spiders like
Pardosa lugubris. These animals hunt prey in direct
attack, and use silk only very sparingly. They find
their prey on the ground, where size abundance and
movement are necessarily quite different from the
lofty heights, where Araneus constructs its trap. And
though Edgar states that his wolf spiders in the field
spend much of their time motionless, it can be *
* Present address: Canadian Wildlife Service, Ottawa,
Ontario K1A OH3.
assumed that they move more in 24 hr than the web
builder with its 30-60 min daily building activity plus
altogether only a few more minutes spent in running
to the entangled prey and wrapping it.
Another strategy for prey-catching is used by those
spiders which build small orb webs plus extensive
“barrier webs”;, The latter supposedly knock-down
prey, which then gets entangled in the trap of the
orb (Kullmann, 1958; Lubin, 1973). Here silk renewal
appears much less frequent (it takes an adult spider
3 days to construct a web) and some structures are
used by several animals together, rather than by a
single Araneus diadematus. This may be a compromise
between the hunting and the orb-trapping methods;
it requires a different distribution of expenditure
between step-energy and silk-renewal-energy. ;
Without trying to provide a total figure for the eco-
logical energetics of the web-builder, we have in this
study undertaken to report on actual measurements
of the energy cost of web-building. Thereby figures
become available to other investigators which
together with observations of life-span, growth, web-
efficiency, prey abundance and many others can serve
as the basis for an assessment of the advantages and
restrictions which orb-web construction presents in
comparison to other prey-catching strategies.
METHODS
All studies were carried out on the cross spider, Araneus
diadematus Clerck. Details on raising and maintaining this
species in, the laboratory have been described previously
(Witt, 19716).
Calculations of the number of steps involved in web con-
struction were made in a frame-by-frame analysis of movie
films. The sequence of events in the construction of an
orb-web have been carefully observed and described, for
instance by Savory (1952). Only the briefest summary can
be given here : The web is constructed within a framework
which in nature may be threads attached to the branches
of a bush and in the laboratory a silken thread runs
around the edges of the box to form a framework (see
Fig. 1). This earliest phase is difficult to record on film.
David B. Peakall and Peter N. Witt
Fig. 1. On this photograph of the web of an adult female
Araneus diadematus Cl. spider, parts of the structure have
been marked; frame, radii and spiral lengths are used—in
addition to movie pictures—to count the number of- steps
employed in construction. Note the relatively large sections
of spiral between neighboring radii in the periphery, which
we counted as 3 steps, as compared to one-step distances
toward the hub. Table shows that in measuring.spiral steps
we discriminated between full, and partial (pendulum)
spiral turns.
as web-building is readily inhibited by the observer’s activi-
ties at this stage (see Salzmann & Witt, 1973). The number
of steps involved initially are estimated from the length
of the frame thread. Then the radii are laid down and
number of steps involved is counted for each radius. A
provisional spiral is then laid from the center out and
finally the sticky spiral -dipd ‘down froth the»utsfde in.
Frame-by-frame observations alldw^one to count* the
number of steps for each section of the spiral as it stretches
from one radius to the next. This number of steps decreases
as the center is approached (Jacobi-Kleemann, 1953). One
step can be roughly defined as one forward plus backward
movement of a front leg (see Fig. 2). In this way the total
number of steps involved in web-building can be arrived
at with reasonable accuracy.
The films were not made concurrently with the oxygen
measurements, but were made earlier on the same species
maintained in cages of the same dimensions. The size, age
and weight of the individuals for the two sets of exper-
iments were closely matched. The potential energy in-
volved in web-building was calculated from still photo-
graphs and the known weight of the spider at the time
of web construction. The technique of photography of the
web has been described previously (Witt, 1971h).
Oxygen consumption was measured by a differential
micro-Warburg apparatus connected to two identical air-
tight transparent plexiglas cages. In some experiments an
empty. cage – was used as a control to that containing the
spider. In other experiments a. non-web-building spider was
used as a control to one active in web-building. Both cages
were placed in a wooden box with plastic windows and
liq and the Warburg apparatus mounted on the lid. The
entire apparathSwas maintained in an air-conditioned
room    Carbon dioxide was absorbed with soda-
lime in a tray at the bottom of the cages.
RESULTS
The number of steps involved in the formation of
a single orb-web are detailed in Table 1. Gold (1973),
re-examining the data of Schmidt-Nielsen (1972),
found that the same energy was expended by all ani-
mals to carry a unit of their body mass one “step”.
For rünning, this figure is 3 x 10“4 cal g-1/step.
If sing this figure, the energy cost of steps involved
in web-building can be calculated. The vertical dis-
tance traveled for1 each radius and spiral turn can
be measured for ea|I web from still photographs. The
total work involved in potential energy, in g cm, can
(a)    (b)
Fig. 2. The spider moves from left to right, laying down spiral turns as she crosses from one radius
to the next. The céphalothorax of the animal points to the right, the left front and hind legs to
the hub of the web. Note that in A the two front legs are on radius 2 and in B the same legs
touch radius 3, having gone one step. The four middle legs may perform several forward and turning
movements during the same period of time; but this is not considered in our calculation (for detail
of movements compare Jacobi-Kleemann, 1953).
The energy budget of an orb web-building spider
189
Table 1. Number of steps and potential energy cost of for-
mation of orb-web (Fig. 1). Weight of spider 115*4 mg
Radius No.    No. of Steps    Vert. Distance cm.    yn1 No.    Vert. Distance cm.
1    22    22.0    i    8.8
2    21    ^ 17.2    • ‘2.;. –    10.6
3    20    15,3    ..’•3. ■    • • lifo
4    18 *    14.0        12.0 ‘.
5    r* Xp    ixfliilf    5    ■vX .
6    .. p ‘    5.0    6    13.8 ^ ‘
7            7    14.8 ,
8    19        8    ii.8 ..
9        8.35* •’        fli:7 ■
10    2i    9.7 ,    • 10    18.0
î*3&&r»«v*    22    12.-8’ : ‘        18.7
,12 1        ■ ij$K:*-    12    19.9
.13 1    19    9.2 ,    ilÿg    . ’ 21} 0″
14,    : il    -, 7(2‘
15    Si        V’ ” i|; – ‘    ‘
16                ‘ ■ 2^, : •
17 ‘    17    1 Xj&gM    17    ;
18 ■    19    7.0    18
19 :        ■ I’fi? ; ‘        ,3.8
20.    20
21 ■ .        16.5
,1|, 11    22    19.7
*’ Tofa^l    ■■    BEfraKê
^numbered clockwise from soiith.
numbered from cehte’r Ou’ty dumber 15-20 are pendulum turns’.
Steps involved in    turns.
■ Spiral    3. steps/.radius    ,3* *30
2-* g ten s^adlusSA.    :!à,
1-4    I 1 steps/radius    =    110
’ Pendulum “tëu/jis’Tiu ■ , ,3 ste p=105
Prov4-‘|’i^ona*l$^^®a 1    7 turns    3×7*x|&fjJ
Steps foil initial frame, considered one complete trip apaundr, É53 cage, number
pf steps estimated from observations    nqnjFW’é^ mil Id in g spider = 240 steps.
Potential energy igijst -2*.x cage height =.’;lb00 g mes
Total steps .418′ é^ÆMi’êÈ^O = 1884
Potential energy ‘    (220    4a^£>+,fl50X    x    0.115 = 63.8 g cm
In cals,• Steps :1884, x ,Jrx 10-4 x 0.115 = 650 x^i’Q’i.^^ÿlî/
P.e.    63. 8    ^#»34 kj!#4, ’ = 150 x 10~4    cal.
.sod    I
then be calculated as the weight of the spider is
known. These values are also detailed in Table 1.
Oxygen consumption was measured under three
conditions. The first represents the basal metabolism
of the spider when it was not involved with web-
building, i.e. no webs were built for 2 days before
or after the measurements were made. The second
is for the basal metabolism of the spider at a time
that it was building a web daily, but not during actual
formation. Third, during the actual period of web for-
mation. No difference was found in the basal metabo-
lism between web-building and non-web-building in-
dividuals (Table 2). During web formation itself the
levels of oxygen consumption were increased by
approx 50% (Table 2).
DISCUSSION
The value for the basal metabolism of Araneus dia-
dematus at 25°C is 360 /d/g per hr (Table 2). This
value is within the range found by Anderson (1970)
for a variety of Arachnids, although it is close to the
upper limit. Anderson did not make measurements
on the genus Araneus, and his measurements were
made at 20°C. For Lycosid spiders, Moulder &
Reichle (1972) give values of 150 /d/g per hr at 15°j
260 /d/g per hr at 20° and 307 /d/g per hr at 25°Cl
These figures show that oxygen consumption data
markedly depend on temperature. Lu bin (1973) gives
values for Nephila which calculate out at 320 /d/g
per hr at 30°C. While no previous data appear to
be available for Araneus, the values obtained here for
the basal metabolism are in line with those obtained
by previous workers on other species of Arachnids,
The use of the oxygen consumption technique does
not appear to have been used previously in the cal-
culation of the energy involved in web formation.
Subtracting the basal metabolism, the oxygen con-
sumption involved in the additional work of web-
building is 144 jul 02/g per hr using a conversion
factor of 1 /d = 0*0048 (Englemann, 1961) and a body
weight of 115 mg, this is equivalent to 795 x 10“4
cals, which is very close to the value calculated by
step-energy (Table 1). This agreement gives exper-
imental validity to the step energy approach for calcu-
lations of the cost of various activities of spiders.
In addition to web-building, an additional cost to
the spider is the formation of the silk protein itself.
Lubin (1973) calculated the energy content of webs
by direct bomb calorimetry. Unfortunately the values
obtained in this way have no biological meaning. This
technique gives the energy required to synthesize silk
from carbon dioxide, water and nitrogen oxides. In
practice the spider starts from aminoadds and further
uses a very effective re-cycling device. Araneus diade-
matus eats its own web daily and re-uses the material
for the next web (Breed et al, 1964).. This process
has been shown to be 92-96% effective (Peakall,
1971). The breakdown of macromolecules to smaller
structures releases energy, while energy must be sup-
plied in the reverse process. In theory there is no
net energy change. Morowitz (1968) calculated that
3*8% of the biomass is oxidized in each cycle. This
figure is in good agreement with previous experiments
in re-cycling (Peakall, 1971). Lubin (1973) gives a
value of 4550 cal/g for the energy needed to recycle
the web; and if the weight of a web of Araneus diade-
matus is 0*1 mg, the energy cost of silk formation
becomes:
4550 x 4 x 10“2 x O f * 10’3
= 182 x 10“4 cals.
The above figures can be used as a basis for the
calculation of the energy involved in various strate-
gies of prey-catching, web replacement and repair.
Spiders confined in cages lead lives rather similar to
those in the wild as far as web building is concerned.
Studies of color-marked individual diadematus show
that webs are built in the same place day after day
(Peakall, 1971). Thus measurements of the energy
budget in the laboratory should be close to the energy
budget of the spider in the natural environment. Ad-
ditional information is required on the frequency and
calorific content of prey. The spiders used, in the cur-
rent study, some 800 x 10“4 cals in web-building and
Table 2. Oxygen consumption of Araneus diadematus
under various conditions
plOg/g/hr    Body weight    Sample
± s.d.    mg ± s.d.    site
Basal rate, spider active in
web-building    360    t    27    101    ±    14    10
Basal rate, spider not active
in web-building**    339    4    34    103    i    12    9
Rate during actual wab-building    504    1    32    99    i    13    9
corrected to 0“C and 760 mm Hg pressure.
*
defined aa no web for two days before and after measurements.
1‘M.V. 54 2 A /
David B. Pi;akall and Peter N. Witt
an additional 200 x 10″4 cals in silk formation. This
is equivalent to about 3000 steps and can be consi-
dered as the capital investment in prey capture. Prey
capture itself costs only about 50 steps. If only a
single item is caught, then the cost is 3000 steps/item,
whereas ten preys reduce this figure to 350 steps/item.
No attempt has been made to assess frequency of
prey capture nor the calorific value of prey. Robinson
& Robinson (1973) have stated that Nephila maculata
renews its orb webs less frequently before egg laying,
but the webs were still functional. This shows that
under especially challenging conditions, Nephik webs
are not renewed and can still be used for several days.
The data for the amount of prey they counted in their
webs in New-Guinea can hardly be transferred to our
Aremeus webs. Lubin (1973) finds the horizontal orb-
barrier-web combination of Cyrtophora moluccensis of
lower trapping efficiency than the vertical Nephik
web and it would be worthwhile to compare their
construction frequency, prey abundance and building
energy with Araneus data, using similar calculations
as ours.
Acknowledgements—Some of the work done in North
Carolina (photography) wa|>supported ‘ih part by grant
No. GB 25274 from the National Science Foundation.
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