Sting Use in Two Species of Parabuthus Scorpions (buthidae )

Scorpions sometimes capture and crush prey with their pedipalps and do not use their sting t o inject venom . Experiments were conducted to test the hypothesis that sting use is selective, resulting in conservation of venom . Sting use in relation to prey size and activity was studied in two African scorpions, Parabuthus liosoma and P. pallidus . Restrictive use of the sting was observed in both species. Decreased use of the sting occurred with decreasing size/resistance of the prey . Also, prey were not stung immediately after being seized , but only after resisting capture . The scorpions did not sting non-resistant prey . These results support the notion that sting use depends upon the size, morphology and resistance of the prey as determined during initia l interactions with the scorpion . Scorpions are notorious for their stinging behavior and powerful venoms. Sting use plays an important role in prey capture and defense (Vachon 1953 ; Cloudsley-Thompson 1958 ; Stahnke 1966). As yet, there have been no controlled and quantitative studies of sting use, but investigators have suggested a variety of factors that ma y be correlated with sting use . It appears that scorpions with large, powerful pedipalps seldom use the sting, while species with small, slender pedipalps readily sting their prey (Stahnke 1966 ; Baerg 1961 ; McCormick & Polis 1990) . Casper (1985) proposed an ontogenetic change in sting use by Pandinus imperator Koch. Young individual s stung prey readily, while older and adult individuals were never observed to employ the sting . Similar results were reported by Cushing & Matherne (1980) for Paruroctonus boreus Girard . Le Berre (1979) noted decreased sting use with smaller prey in Buthus occitanus Amor., and similar observations were reported for other species (Pocock 1893; Vachon 1953 ; Cloudsley Thompson 1958 ; Baerg 1961 ; Biicherl 1971 ; Polis 1979) . The purpose of this study is to examine stin g use during prey capture by two East African buthids, Parabuthus liosoma Hemprich & Ehrenberg and Parabuthus pallidus Pocock . Both species used their stings selectively, depending upon the size, morphology and resisting behavio r of the prey. Results are discussed in terms of the costs and benefits of venom injection during pre y capture . METHOD S Natural history . —Parabuthus liosoma and P . pallidus are found in several countries in Eas t Africa (Probst 1973) . Adults of the former species are of medium size for scorpions and have a yellow to yellowish-red body, except for part of the cauda and telson which are dark red/brown . They have small, slender pedipalps and a thick, powerful cauda. Similar coloration and morphology is present in P . pallidus, but these are slightly smaller and lack the darkened distal part of the cauda . There are no previous reports on the life history or behavior of these species . Materials .—Individuals of P . liosoma and P . pallidus were collected in the vicinity of Isiolo , Kenya in May and June, 1988 . The animals were found in the same semi-arid area under stones along roadsides, but no more than one scorpio n was ever found beneath a single stone. The substrate consisted of compacted sand with occasional grass and bushes . The scorpions were taken to Norway, wher e 11 individuals of P . liosoma and 12 individual s ofP . pallidus were used in the experiments . The specimens were of unknown age and ranged in length (proand mesosoma) from 18-32 mm (x = 25 .1 mm, P . liosoma) and 13-31 mm (R = 21 .3 mm, P. pallidus) . Specimens were kept individually in terrari a (32 x 20 cm), with a substrate of sand and som e stones . The temperature was held at 24-30 °C , and the light/dark period was 10:14 hr . Water was provided weekly by misting . Animals were