Summary
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1.
The response of many scorpions to a light touch is a vigorous convergence of the sting and the pedipalps towards the stimulated point (defensive strike response). They respond to a puff of air by pulling the pedipalps in towards the mouth, erecting the tail and scuttling backwards (defensive withdrawal). Response times of 20 to 150 msec have been measured for these two reflexes.
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2.
The defensive strike appears to be initiated by small receptors scattered over the surface of the legs and other parts of the body, and not by conspicuous structures such as long hairs and lyriform organs, nor by any variety of joint receptor.
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3.
Lesions in the cephalothoracic mass can unilaterally abolish the defensive strike while sparing locomotory and leg withdrawal movements. Sectioning one of the two connectives immediately behind the c.t.m. has no effect.
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4.
The strike pathway is characterized by strong resistance to habituation, graded response, and (at least in one species) longitudinal lability indicated by independent movement of the tail and pedipalps. Thus, in spite of its rapidity, the defensive strike does not closely resemble the evasive responses of the cockroach and earthworm.
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5.
Bilateral stimulation elicits a symmetrical response. Other attempts to modify the response, for example by altering or disrupting the proprioceptive input, have failed.
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This work was performed while one of us (J. P.) was a Fulbright Lecturer at Sri Venkateswara University. Dr. R. P. S. Reddy, Museum National d'Histoire Naturelle, Paris, kindly identified the species used in these experiments. We are grateful to T. H. Bullock, J. A. L. Cooke, G. A. Horridge and especially D. C. Sandeman for critical reading of the manuscript.
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Palka, J., Babu, K.S. Toward the physiological analysis of defensive responses of scorpions. Zeitschrift für vergleichende Physiologie 55, 286–298 (1967). https://doi.org/10.1007/BF00349604
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DOI: https://doi.org/10.1007/BF00349604