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Herms (W. B.). The Pajaroello Tick {OrnitJiodorus coriaceus, Koch), 

 with special reference to life-history and biting habits. — Jl. of 



Parasitology, Urbana, III, ii, no. 3, March 1916, pp. 137-142, 1 fig. 



The venomous Pajaroello tick is much feared in the mountainous 

 portions of Santa Clara and San Benito Counties, Cahfornia. The 

 accounts all agree in the essential detail that the bite results in an 

 irritating lesion which is slow to heal and often leaves an ugly deep 

 scar. In August 1913, living specimens taken near Mount Hamilton 

 were identified as Ornithodorus coriaceus, Koch, described in 1844 

 from a single female specimen from Mexico, which is probably the 

 original habitat. This Argasid superficially resembles 0. moubata, 

 Murray, which transmits relapsing fever in Africa. Since August 1913, 

 its complete life-history has been worked out. The larvae from 323 

 ova, deposited by one female on 9th March 1914, hatched in about 21 

 days at a temperature averaging 79° Fahr. They were placed on the 

 ear of a rabbit on 2nd May, and, among others, one was recovered fully 

 engorged on 11th May. Its first moult occurred on 21st May, giving 

 about 51 days for the larval stage in this instance. The second moult, 

 without a second engorgement, took place on 15th June. The nymph 

 became fully engorged in about twenty minutes on 2nd July, the third 

 moult occurring on 12th August. Becoming fully engorged again 

 on 11th October, the fourth moult took place on 23rd December. 

 Engorging again on 16th January 1915, the fifth moult took place 

 9th March and the mature tick, a female, appeared. On 27th March it 

 became fully engorged on a mouse and was placed with a male 

 on 16th April, pairing taking place on 17th April. The first 

 oviposition consisting of 428^ eggs took place on 10th June 1915. 

 Thus the period from egg to egg in this individual covered 

 exactly fifteen months. This time may be reduced very considerably 

 by applying the ticks to a suitable host at shorter intervals and in 

 the case of one male sexual differentiation was accomphshed in 159 

 days, as against 343 days in the above instance. Under natural 

 conditions it seems quite probable that there is one generation eack 

 year and that two years may be necessary in many instances. Although 

 the incubation period at a given sustained temperature suft'ers little 

 variation, e.g., at 79° Fahr. it is 21 days, the length of time required 

 for the other stages varies considerably. The minimum length of the' 

 larval period was found to be 19 days. The number of moults varies 

 from four to seven. The length of time a female may remain fertile 

 without further pairing is at least two years. No little difficulty was 

 experienced in rearing this tick. The ear of a rabbit is best suited for 

 feeding the larval stages ; later stages are best fed by placing the 

 ticks either on a rabbit or on a mouse, holding these until the fully 

 engorged ticks drop off, this process requiring from 15 to 20 minutes. 

 The venomous nature of the bite of this tick as affecting man, monkey 

 {Macacus rhesus), rabbit and mouse is described. In the animals the 

 injury did not prove severe. A detailed account of two bites suffered 

 by Mr. W. L. Chandler is given. Considerable irritation and swelUng 

 was produced and for several weeks both lesions exuded a clear 

 lymph from beneath a scab, which remained in evidence for two or 

 three months. Mr. Chandler reported these ticks as very numerous in 

 some locahties. Their presence and number seemed to be determined 



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