INTRODUCTION

Almost two millennia ago, the wonders of tick osmoregulation and excretion were commented upon by Pliny the Elder (AD 23–79) in his 37-volume Historia Naturalis when he wrote: ‘a tick simply filled to bursting point with its victim's blood and then died because it had no anus’ (from Hillyard, 1996). A millennium and a half later, the Reverend Dr Thomas Moufet (1553–1604) also noted in his Insectorum sive Minimorum Animalium Theatrum that ‘[Ricinus] is filled with food abundantly and yet there is no passage for any excrement’. Quite correctly, these ancient natural historians observed the tremendous increase in body size of feeding female ticks and then suddenly these engorged ticks would detach and fall to the ground, barely able to move with their enormous rounded bodies, and unwilling to reattach. However, the conclusions of Pliny and Moufet were incorrect that this apparent onset of tick ill-health was due to an inability to excrete caused by the lack of anus or that these inactive engorged females would die as a result. Indeed, if Pliny and Moufet had continued their observations of ticks for a few weeks, they would have seen that these engorged females (most likely Ixodes ricinus) would deposit several thousand eggs before dying, thus completing the life cycle. Ticks do possess an anus and excrete a small amount of nitrogenous waste (mainly guanine).