Mastigoproctus giganteus. Used with permission. (c) Bryan E. Reynolds.

Form and Function

Mastigoproctus giganteus pedipalps. Used with permission. (c) Bryan E. Reynolds        Mastigoproctus giganteus are typically 3.5 cm to 7.5 cm long when fully grown. (Drees and Jackson 1999, Hembree 2013). Like all Arthropods, they possess a hardened cuticle, segmented bodies, jointed limbs, and have the feature of molting (Budd and Telford 2009). See Classification for more phylogenetic details of M. giganteus.
        M. giganteus has a set of large pincers as their mouthparts called pedipalps, which they use to crush their prey and dig burrows in the surrounding soil. Their rear three sets of legs are used for walking and the foremost pair are thin appendages used as sensory structures for feeling the Vinegaroon’s surroundings (Drees and Jackson 1999, Punzo 2007).
        Female Vinegaroons are generally larger than males (Punzo 2007), but males have much larger pedipalps (Weygoldt 1970). M. giganteus reproduces through sexual reproduction and the females carry their eggs in a clear sac attached to the female’s Female Mastigoproctus with egg sac. Taken from Wikipedia Commons.gonophore. After the larvae develops, the young whipscorpions will climb onto the abdomen of their mother and stay there until they have developed enough to live independently (Schmidt 2009). See Life History and Reproduction for more details on this process.
            M. giganteus secretes a chemical spray that has been shown by several scientific studies to be 83-84% acetic acid, 11% water, and 5% octanoic acid with only trace elements of other chemicals (Eisner et al. 1961, Schmidt et al. 1999). You are most likely familiar with acetic acid, as it is the primary component of vinegar—thus the common name Vinegaroon. While acetic acid is harmless to be ingested or in the mouth in small concentrations, at 84% it can irritate and burn, and more importantly, it can be severely damaging to the sensory or respiratory systems of other organisms. At these points, the chemical compound can directly contact nerve endings and has very little chance of being diluted. The chemical spray is used for protection, and is not thought to be used as a predation strategy by the Vinegaroon (Eisner et al. 1961, Schmidt et al. 1999). To learn more about M. giganteus’s predation habits, visit the Interactions page.
Mastigoproctus giganteus preparing to spray. Used with Permission. (c) Bryan E. Reynolds         The chemical spray of the Vinegaroon is secreted by the pygidial gland, which consists of two thinly walled sacs that sit in the abdomen of the organism, and are connected by ducts to two controlled slits in a knob at the base of its tail (Eisner et al. 1961, Schmidt et al 1999). The spray is released when M. giganteus comes in direct contact with a predator. The acidic chemical concoction is discharged from the opening of the slits at the base of its signature whip-like flagellum, which extends from its rear (Eisner et al. 1961, Kern and Mitchell 2011). The spray is released as a mist of fine droplets, and is usually aimed on the portion of the M. giganteus’s body that is being attacked (Eisner et al. 1961, Schmidt et al. 1999). This way the spray is most likely to come in contact with the head, and most importantly the sensory systems, of the attacker, where it will be most effective. The spray is aimed by the large knob at the base of the flagellum and has a maximum range of around 80 cm (Eisner et al. 1961). To see a video of M. giganteus releasing its spray, click HERE. Since the spray is released from the base of the tail, the purpose of the long tail has often been brought into question. However, it has since been determined that because the rear of M. giganteus is the weak point in its hardened armor, the whipping tail can serve as protection by preventing predators from accessing the posterior of the Vinegaroon (Schmidt 2009).
        It has been suggested that chemical defenses in arthropods arose as a defense mechanism specifically because of the selective pressure of vertebrate predators, who are much quicker and more agile, making arthropods that are not equipped with defenses an easy target for these vertebrates (Evans and Schmidt 1990). This is most likely the reason the chemical secreting, pygidial gland arose in
M. giganteus.

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