Introduction

All scorpions hunt for prey to survive. Scorpions aren't picky eaters. They'll go for anything their size or smaller. A scorpion might even take a prey that's larger than it is, using its venom to kill or paralyze it. It all depends on where a scorpion lives, what its foodsource is and its species, but generally we're talking spiders, insects, small mammals and birds and even lizards and snakes! Rather than using vision or audition to locate their prey, scorpions have been found to use specialised neurosensory systems. For example, the pectines below the scorpion's body have been suggested to pick up chemical signals that resemble pheromones, in order to sieze their prey. In addition, all parts of the scorpion's body is covered with coarse hair - but not all are involved in traction and location of prey. They possess a few specialised hair, called the trichobothria (singular : trichobothrium), are receptive enough to be able to allow the scorpion to hunt for prey. The trichobothria are known to respond to movements and the vibration of air, and the strategic location of trichobothria on the padipalps of the scorpion aids them in the detection of other scorpions and prey items. Interestingly, different species of scorpions have a different placement of trichobothria which remains consistent within the same specie. As such, the location and number of trichobothria have been used by taxanomists to distiguish the various taxa, genus or species. There had been a classification of sensory hairs in 1964, into 4 main categories (excluding the trichobothria) : TYPE 1 : Thin, about 0.2 mm long, not visible to the naked eye ; found widely over the body, covering the telson extensively. TYPE 2 : Thin, about 1 mm long, barely visible to the naked eye ; found in all parts but mainly covering the pectines, intersegmental membranes of the measoma, pedipalps, telson and legs. TYPE 3 : Only about 5-6 in number, 0.5 to 1 mm long, invisible to the naked eye ; found only on the dorsal side of the legs. TYPE 4 : Coarse, curved and spiny, 1-1.5 mm long, covering the tarsi of the legs. The type 1 hairs have been reported to be thermal receptors and the type 3 hairs are the humidity and tactile receoptors. These hairs are in fact the main instruments of navigation scorpions have. Do the scorpions have a strategy in catching their prey ? No. Not exactly. Most of them are "sit and wait" predators that ambush unwary victims. They would wait near their burrows, and springout suddenly when any potential movement comes close - this is probably "sensed" by the scorpion's sensitive hairs. Most of the scorpions will consume and digest their prey at the site of capture and eventually return to their burrows. However, some odd-ones-out do exist. Buthus occitanus have been reported to return to their burrows with subdued prey. Other scorpions have a more active approach to obtaining food - by hunting, mostly at night when it is cooler and they are less prone to dehydration. Tree-dwelling (arboreal) scorpions such as Uroplectes vittatus and U.otjimbinguisis have been observed to have moved around at night about the branches of acacia trees, looking for food. The Bark Scorpions (Centruroides sp.) have also be known to go round chasing prey.

Protection

Scorpions aren't without enemies either. They're well-protected against any attack: think pinchers, think armor and think scorpion venom, but some creatures are either immune to their stinges or have skins so thick the venom doesn't have any effect. Other animals have come up with different tactics to ward of scorpion attacks and make meals out of them. The list of predators is almost the same as the list of prey: again mammals and birds, insects, spiders, frogs and salamanders.

Scorpions eating scorpions?

And scorpions! Big scorpions eat little scorpions and female scorpions eat male scorpions in some species, and in others it's the male who eats the female after mating. Scorpions will even eat other scorpions of the same species! Because scorpions can live in areas where other species are few, like a desert, sometimes scorpions will be a scorpion's main foodsource! Such cannibalism is not uncommon, then. Even among mother-and-child scorpions, the mother will cannibalize any young that is considered weak. Such maternal cannibalism have been observed to occur either when the young fall off her back and is unable to re-mount the mother, or when the mother is very stressed due to undue disturbance. So, if scorpions of the same species munch on each other, the the belief that they are immune to their own venom is untrue ? No. Scorpions ARE immune to their own venom, but only to a certain extent. Shulow and Levy (1978) has found out that the Buthid scorpion Leiurus quinsquestriatus, normally called the "Deathstalker", is very resistant to its own venom. For death to occur, the scorpion would need to be directly overdosed in a short period of time. For Leiurus quinsquestriatus, it has been found that the quantity of venom that is required for death to occur would amount up to 18 stings by an average adult of the same species. This might not be very possible, since the probability of the attacking scorpion getting a "hit" each time, for 18 consecutive times, is very low. How then, can scorpions cannibalise each other ? This is done when the larger scorpion overturns the smaller one, and stings it directly into an abdominal ganglion - this results in instant death. But is cannibalism a rare occurance, or is it normal at all ? From various data, it seems that it is commonplace for scorpions to eat each other. A study on the diet of Parauroctonus mesaensis by Polis (1979, 1980b) showed that scorpions were the 4th more commen prey item in their diet, and an average of 9% of their diet ! Hence, it seems that scorpions do live in a terrible world of being eaten frequently by their own friends !

References

Polis, G.A. 1979. Prey and feeding phenology of the desert sand scorpion Parauroctonus mesaensis (Scorpionidae; Vaejovidae). Journal of Zoology (London) 188;333-46. Shulov, A., and G.Levy. 1978. Venoms of Buthinae. A, Systematics and Biology of Buthinae. In Bettini, ed., pp.309-12. Abushama, F.T. 1964. On the behaviour and sensory physiology of the scorpion Lieurus quinsquestriatus (H&E). Animal Behavior 12(1):140-53.