Araneae, Uloboridae)

1998 . The Journal of Arachnology 26 :392-396 RESEARCH NOTE COOPERATIVE PREY CAPTURE IN THE COMMUNAL WEB SPIDER, PHILOPONELLA RA FRAYI (ARANEAE, ULOBORIDAE) Prey capture advantage has played an im- building spider that occupies the tropical rain portant role in the evolution of communal or forest undergrowth of peninsular Malaysia social spiders (Shear 1970 ; Rypstra 1985, (Simon 1891; Masumoto 1992). I studied this 1986 ; Buskirk 1981 ; Uetz 1986, 1989). Com- species in the Pasoh Forest Reserve in Negri munal web organization may improve prey Sembilan state, Malaysia . A colony of P. raf- capture in two ways : 1) it may improve the frayi is composed of individual orb-webs con- ability of webs to intercept prey (the "ricochet nected to one another by non-adhesive silk . effect") (Uetz 1989), and 2) it opens the pos- All uloborids lack poison glands and must rely sibility of communal prey immobilization that on wrapping to subdue prey (Lubin 1986) . may allow spiders to capture larger and pre- The average body length of this species is sumably more profitable prey. Communal cap- 6.21 mm in females and 3 .15 mm in males ture of large insect prey has been observed in (Masumoto 1992). The volume of colonies is a number of social web-building spiders, such variable according to the number of individ- as Agelena consociata Denis 1965 (Krafft uals in the colony (Table 1) . The age of adult 1969), Anelosimus eximius (Keyserling 1884) females is easily determined by their body (Vollrath & Rohde-Arndt 1983 ; Christenson color. Adult females are orange for at least a 1984; Pasque & Krafft 1992), Mallos gregalis week after the final molt, becoming black a (Simon 1909) (see Jackson 1979), and it has few weeks later. been demonstrated that communal spiders I conducted field observations in a 2 ha re- capture larger prey than solitary spiders (Bus- search area from February-April 1992 and kirk 1981 ; Nentwig 1985; Uetz 1986) . also in March 1993 . All colonies found within Members of the genus Philoponella Mello- this area were included in the study. To locate Leitao are known to construct communal these colonies, I searched within the study webs, but most have been reported to employ area for 3 days before the 25 February and the only non-cooperative prey capture (see Bur- 17 March study periods . All observations gess 1978 ; Buskirk 1981 ; Smith 1982 ; Lubin were made between 0800-1800 h, which cor- 1986). However, cooperative prey capture has responded to the daylight periods in this area . been reported in a few species of Philoponella I recorded the number, stage of maturation and (see Breitwisch 1989 ; Binford & Rypstra behavior of spiders in colonies on 25 February 1992). To understand the diversity of coop- and 17 March 1992 . In March 1993, I also erative prey capture and social behavior in the conducted a total of 17 hours of field obser- genus Philoponella, the prey capture behavior vations on the only colony (4633Y) still pres- of as many species as possible should be de- ent in the study area. For this colony, I re- scribed. corded the stage of maturation, relative body This study describes the colony composi- length of interacting individuals and each in- tion and prey capture handling behavior of the sect that entered the colonial web. Individuals uloborid spider Philoponella raffrayi (Simon were not marked and the relative body length 1891) and determines if the efficiency with between the spider and the insect prey was which they capture large insects is higher estimated by eye . I collected females and their when spiders hunting cooperatively than when egg sacs from the No. 2 colony described be- they hunt singly. low. I preserved them in 70% alcohol and Philoponella raffrayi is a communal web- counted the number of eggs per egg sac and, 392 Table 1.-The composition of Philoponella raffrayi in the research area of Pasoh Forest Reserve on 25 February and 17 March 1992 . Between the two dates, colonies #7 and 8 disappeared, and the new colonies #9, 10, 11, 12 appeared in the study area . The asterisk (*) or double asterisks (**) indicates the number of Argyrodes spp. or Portia spp., respectively. The single dagger (j- ) indicates that of 24 females, 17 had produced eggsacs by 17 March . 25 February 1992 17 March 1992 No . of No . of Colony size No . of No . of Colony size adult adult No . of (cm) (length, adult adult No. of (cm) (length, Survivorship Colony females males juveniles Other width, females males juveniles Other width, (D+E+F/ No . (A) (B) (C) species height) (D) (E) (F) species height) A+B+C) 1 0 0 28 0 30, 30, 60 20 1 0 0 40, 40, 60 75% 2 24 1 0 1* 60, 60, 60 24t 1 0 4* 70, 60,70 100% 3 25 7 0 0 55, 55, 32 23 1 0 1*, 1** 60, 60, 35 75% 4 0 0 35 0 20, 15, 30 0 0 25 0 40, 40, 60 71% 5 44 2 0 0 70, 40, 70 44 0 0 0 200, 150, 150 96% 6 6 0 0 0 10, 15, 15 4 0 0 0 30, 20, 20 67% 7 15 0 0 0 40, 40, 40 - - 8 15 5 0 0 30, 30, 30 9 - - 28 2 0 1** 80, 80, 80 10 4 0 0 0 40, 40, 40 11 3 0 0 2* 20, 20, 20 12 14 1 0 0 40, 50, 40 394 THE JOU AL OF ARACHNOLOGY Table 2-The number of prey entering the col- 140- ony, captured or not captured, in a colony of Phil- oponella raffrayi. Relative prey size is the ratio of prey body length to spider body length . IN 130 - W Relative prey size (prey/ Cooper- spider) Single ative <0.1 Success 30 1 110 Fail 1 0 Efficiency (%) 97 100 0.1-0.5 Success 32 2 S 100 Fail 4 0 1 .3 1 .4 1 .5 1 .6 1 .7 1 .8 Efficiency (%) 89 100 0.5-1.0 Success 1 4 Ceph lothorax Width (mm) Fail 11 0 Efficiency (%) 8 100 Figure 1 .-The co elation between the cepha- 1 .0< Success 0 0 lothorax width of fern es and the number of eggs Fail 6 0 deposited. Spearman's ank correlation: Rs = 0.523, Efficiency (%) 0 n = 15 . P = 0.046. April in 1992, and he juveniles remained in under a binocular microscope, measured to the the same colony wh e they had hatched. De- nearest 0.1 mm the width of females' cepha- velopmental stages f females were synchro- lothorax. Two of them were deposited as nous within the sam colony, but not synchro- voucher specimens in the collection of the De- nous among differe colonies . Furthermore, partment of Zoology, National Science Mu- the number of spide s in the same colony nev- seum, Tokyo (NMST Ar 3514, 3525) . Capture er increased, and n fusion of colonies was efficiency is defined as the ratio of the number observed. During A ril, no colonies remained of insects captured compared to the number at the same web sit and three colonies, each of insects entering the webs . containing more tha 100 juvenile P. raffrayi, I observed eight colonies in February and appeared at differe web sites . All adult fe- ten colonies in March 1992 (Table 1) . Each males disappeared f om the juvenile web col- colony consisted of members of a similar de- ony, and I could det ct no parent-offspring in- velopmental stage, apparently representing teraction except or egg sac guarding . only variation in size of the same instar. Be- Furthermore, Argyrodes and Portia were tween 25 February-17 March (3 weeks), six found in the coloni s. of the eight colonies remained at the same During the obser ation, I recorded 92 in- web site, but two colonies disappeared from sects of four order entering webs ; Diptera the study area and four colonies newly ap- (75), Hymenoptera 15), Coleoptera (1), Lep- peared. In March 1992, females of No . 2 col- idoptera (1 larva). 0 these insects, the spiders ony produced twig-like egg sacs, hung them captured 66 Dipter two Hymenoptera, one from the hub and began guarding the eggs . Coleoptera and on larva of Lepidoptera . The mean number of eggs per egg sac was Wrapping was do nantly conducted by in- 118 ±9 .96 (x ±SD, n = 15). This value was dividual females . owever, when prey was correlated with the cephalothorax width of its trapped in the perip ery of an individual orb mother (Spearman's rank correlation ; Rs = web, 7 out of 70 prey items (10%) were 0.523, n = 15, P = 0.046 ; Fig. 1) . However, wrapped by two c operating females. They 8 of 13 females measured had a cephalothorax first subdued prey b throwing silk on it from width of 1 .5 mm but produced 101-132 eggs. a distance and beg n to more tightly wrap Factors that may have contributed to the dif- prey cooperatively a they rotated it. The prey ference would be energy gain during the adult capture efficiency of a single females was 89- stage. Oviposition occurred between March- 97% when prey size was less than the half the MASUMOTO-COOPERATIVE PRE' CAPTURE 39 5 body length of the spider, but this decreased Burgess, J .W. 1978. Social behavior in group-liv- to only 8% when the relative prey size was ing spider species . Symp . Zool . Soc . London ., between 0 .5-1, and no prey was captured 42 :69-78. when the prey length was greater than spider Buskirk, R .E .

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