Prey and Feeding Behavior
Scorpions are nocturnal predators whose prey consists mostly of insects, spiders, and other scorpions. As predators, they tend to be generalists, capturing and eating whatever subduable prey comes their way. One scorpion species from the sand dunes of southern California, Smeringurus mesaensis, was found to eat over 100 different prey species in a five-year period, including beetles of many types, winged termites and ants, wasps, bees, moths, true bugs, crickets, roaches, flies, spiders, and scorpions (of the same and other species)(Polis 1979). Some of the larger scorpions may occasionally take small vertebrates, such as lizards and mice. Scorpions are important consumers in some communities. Scorpio maurus was reported to eat an annual average of 11% of the Israeli isopod population (Shachak & Brand 1983), Urodacus yaschenkoi 7.9 kg/ha of invertebrate prey in Australia (Shorthouse & Marples 1982).
Although scorpions are noted for cannibalism, the frequency of this phenomenon in nature is directly correlated to their population densities (abundance) and the species of scorpion involved. In some sand dune habitats where densities are very high (up to 1600 scorpions/acre), scorpions of the same or different species may constitute about 10% of the diet for S. mesaensis (Polis 1979); in other areas where scorpions are not as abundant, cannibalism is rarely observed. It is also interesting to note that scorpions of a few tropical species are quite tolerant of one another, permanently living together in colonies of overlapping generations and sharing prey (Polis & Lourenço 1986). Species of Centruroides in the American Southwest are frequently found together under the same rock or log, and are known to aggregate in fairly large numbers during the winter (McAlister 1965).
The methods by which scorpions locate and capture their prey are quite sophisticated. Although scorpions can see fairly well, detecting nearby shapes on dark nights (Fleissner, 1977), it is generally accepted that they mostly utilize other sense organs for prey detection. The first of these are fine hairlike trichobothria that are distributed on their pedipalps. These trichobothria are so sensitive that they are moved by air-borne vibrations (such as those a flying insect would generate), which trigger a nerve impulse that alerts the scorpion. Scorpions have been observed reaching into the air with their pedipalps when moths are fluttering nearby and more than a few captures have been witnessed by blacklighting researchers.
The other sense organs of critical importance to prey detection are called slit sense organs. The slit sense organs have been well-studied in sand specialists, but little is known of their functioning in scorpions inhabiting other substrates. The organs are located near the tips of the legs and cannot be seen with the naked eye. They work much like seismographs, gathering and interpreting compressional waves in the soil or sand that would be generated by a walking insect. These small organs can provide the scorpion with information regarding the direction and distance at which potential prey are situated.
Scorpions with slender pedipalps are prone to sting their prey, whereas those with robust pedipalps tend to crush prey mechanically, reserving the sting for large or strong prey. All use the pedipalps to manipulate prey, tearing pieces off with the chelicerae to be digested in a preoral cavity before being sucked into the gut.
Fleissner, G. 1977. The absolute sensitivity of the median and lateral eyes of the scorpion, Androctonus australis L. (Buthidae, Scorpiones). Journal of Comparative Physiology 118A: 109–120.
McAlister, W. H. 1966. The aggregating tendency of Centruroides vittatus Say (Arachnida, Scorpionida). Texas J. Sci., 18:80-84.
Polis, G. A. 1979. Prey and feeding phenology of the desert sand scorpion Paruroctonus mesaensis (Scorpionida, Vaejovidae). J. Zool., London, 188:333-346.
Polis, G.A. & Lourenço, W.R. 1986. Sociality among scorpions. In: Proceedings of the 10th International Congress of Arachnology, Jaca 1: 111–115.
Shorthouse, D.J. & Marples, T. 1982. The life stages and population dynamics of an arid zone scorpion Urodacus yaschenkoi (Birula, 1903). Australian Journal of Ecology 7: 109–118.
Sissom, W.D., Polis, G.A. & Watt, D.D. 1990. Field and Laboratory Methods. In: Polis, G.A. (Ed.) The Biology of Scorpions. Stanford University Press, Stanford, CA, 445–461.