Twenty-nine colonies of a population of the cooperative spider Stegodyphus sarasinorum Karsc h (Eresidae), from two sites in Bangalore, Karnataka State, India, were examined using protein allozyme electro phoresis . Thirty-five enzyme systems were examined . Twenty-two enzymes (the products of 25 putative loci) gave scorable results . Lactate dehydrogenase (LDH) and glucose-6-phosphate dehydrogenase (G6PDH) wer e polymorphic with two alleles each; hexokinase exhibited uninterpretable variation . The rest were monomorphic . One LDH allele was found at only one of two collection sites, and one G6PDH allele was found only at th e other collection site . The pattern of variation in S. sarasinorum is similar to that found in three other studies of cooperative spiders : extreme population subdivision, with most colonies consisting of identical homozygotes . Stegodyphussarasinorum Karsch (1891) is one of three permanently cooperative species in th e genus Stegodyphus (Kraus & Kraus 1988) . S . sarasinorum has been found in India, Sri Lanka , Nepal and Afghanistan (Kraus & Kraus 1988) . The natural history of S. sarasinorum has bee n investigated by Jambunathan (1905), Bradoo (1972, 1975, 1980), Jacson & Joseph (1973), an d Kraus & Kraus (1988) . Individuals live in large cooperatively built colonies with a nest or retrea t constructed of silk woven together with leaves , twigs, and remains of food, and a sheet web fo r prey capture (Jacson & Joseph 1973) . Prey capture is also a cooperative effort and when th e prey has been subdued many spiders may joi n in the feeding, even those who did not participate in the actual prey capture activities (Bradoo 1980). The females care for young during the first fe w instars by feeding the spiderlings (Bradoo 1972) . When the young become old enough they begi n capturing their own prey and sometimes feed upon older females that die within the nest (Bradoo 1972) . Like other cooperative spiders (Pai n 1964 ; Darchen 1967 ; Jackson & Smith 1978 ; Fowler & Levi 1979 ; Aviles 1986 ; Rowell & Main 1992), S . sarasinorum colonies exhibit strongly female-biased sex ratios with 0 .15 to 0 .28 males for every female (Jacson & Joseph 1973) . These spiders are tolerant of individuals from othe r nests (Kullman 1968), and migration among colonies in close proximity has been observed (Bradoo 1972) . 'Current address : Dept . of Entomology, Comstock Hall, Cornell University; Ithaca, New York 14853 USA Little is known about dispersal, population structure or mating in S. sarasinorum . Another cooperative species of Stegodyphus, S. mimosarum, is known to balloon (Wickler & Seibt 1986) . Jambunathan (1905) and Jacson & Joseph (1973) both record ballooning by immatures o f S. sarasinorum, but this has not been examined to determine ballooning's importance in the dispersal or colony foundation of S. sarasinorum . Bradoo (1972) reports that new colonies wer e established by spiderlings that left the main colony to form daughter colonies connected to the mother nest by common web sheets . Brado o (1980) reports that new colonies were also forme d by gravid females who had left the original nes t and formed new nests in which to keep thei r cocoons . In this study we used protein allozyme electrophoresis to examine genetic variation withi n and among colonies of S . sarasinorum collected from two sites in south central India .