Predators & Parasites
Although scorpions are quite formidable creatures armed with venom and pincers, they fall prey to many different kinds of animals. Recent surveys of the literature (Polis, et al., 1981; McCormick & Polis 1990), have revealed over 100 different kinds of scorpion predators, ranging from web-building spiders and centipedes to a variety of lizards, birds, and mammals. Many scorpions are notoriously cannibalistic or feed on other scorpion species in their community. Among invertebrates, the predator-prey relationship is generally size-determined: the larger animal will eat the smaller one. For example, a large centipede might subdue a smaller scorpion; however, a large scorpion will most likely subdue a smaller centipede. The same is also true for scorpion-scorpion encounters.
For obvious reasons, many vertebrates that feed on scorpions often attack and break the tail of the scorpion before eating it. Tail-break behavior has been reported in grasshopper mice, elf owls, and shrews, to name a few. Pallid bats (Antrozous pallidus) of the Southwest are known to land next to a scorpion, crawl over to it, break the tail in capturing it, and then fly off to find a place to feed. Dramatic film sequences showing predation by these bats, as well as by meerkats (in South Africa) and “sand-swimmer” snakes (Chionactis sp. in the Sonoran Desert) have been relayed to the general public in TV nature programs. Many predators of scorpions, including meerkats and Chionactis snakes, are also immune to the venom. Lastly, it should be noted that the large black scorpions of Asia and Africa are often eaten by native peoples.
Mortality is highest immediately after birth, lower for individuals of intermediate age, and high for adults. For example, 65%, 30%, and 60% per year for the Australian Urodacus manicatus (Smith 1966). Mortality is particularly high among males due to increased mobility during breeding season and cannibalism by females. Biased adult sex ratios of 1.2-1.4:1 are typical (Polis 1990).
It is common to overlook parasites in studying ecological interactions, and scorpions are known to have their fair share (McCormick & Polis 1990). Nematode worms are occasionally found in their body cavities, but their most common parasites appear to be mites. These small mites, usually orange or whitish in color, attach themselves to the exterior of the scorpion, either directly to the body segments or to the softer membranes between the segments. The amount and nature of damage they inflict to the scorpion is unknown, but even scorpions fairly heavily parasitized appear healthy. There is another interesting parasite of scorpions. A recent report by Williams, et al. (1990) provided a detailed description of a tachinid fly whose larvae parasitize two species of scorpions in the western states; in both cases, the scorpions were found alive with two fly larvae living inside their abdomen. The developing larva consumes the internal organs of the scorpion, eventually killing it, and emerges from the carcass shortly after pupation.
McCormick, S. J.and G. A. Polis. Prey, Predators, Parasites. In: Polis, G. A. (Ed.) The Biology of Scorpions. Stanford University Press, Stanford, CA, 294-320.
Polis, G.A. 1990. Ecology. In: Polis, G.A. (Ed.) The Biology of Scorpions. Stanford University Press, Stanford, CA, 247–293.
Polis, G. A. , W. D. Sissom, and S. J. McCormick. 1981. Predators of scorpions: field data and a review. Journal of Arid Environments, 4: 309-326.
Shachak, M. & Brand, S. 1983. The relationship between sit-and-wait foraging strategy and dispersal in the desert scorpion Scorpio maurus palmatus. Oecologia 60: 371–377.
Smith, G.T. 1966. Observations on the life history of the scorpion Urodacus abruptus Pocock (Scorpionida), and an analysis of its home sites. Australian Journal of Zoology 14: 383–398
Williams, S. C., P. H. Arnaud, Jr., and G. Lowe. 1990. Parasitism of Anuroctonus phaiodactylus (Wood) and Vaejovis spinigerus (Wood)(Scorpiones: Vaejovidae) by Spilochaetosoma californicum Smith (Diptera: Tachinidae), and a review of parasitism in scorpions. Myia, 5: 11-27.