L I B R.ARY OF THE U N IVER.SITY Of ILLINOIS cop. 2 '.AiUKAL HISTORY SURVEY STATE OF ILLINOIS William G. StraHon, Governor DEPARTMENT OF REGISTRATION AND EDUCATION Vera M. Binks, Director ECTOPARASITES OF THE COTTONTAIL RABBIT In Lee County, Northern Illinois Lewis J. Stannard, Jr. Lysle R. Pietsch *fT!Hh>i NATURAL HISTORY SURVEY DIVISION Harlow B. Mills, Chief Biological Notes No. 38 Prinfed by Authori+y of the State of Illinois Urbana, Illinois June, 1958 OCT : 1358 l.. Collecting varied in intensity according to the time that could be given to the study. The senior author sorted, identified, and counted the ectoparasites. Occasionally a rabbit was caught several times within a season. For example, a rabbit designated as Peter II was caught nine times in July and August, 1952, and each time all the ectoparasites found on it were removed and preserved. Other rabbits. No. 57 and No. 307, were caught five times each; several were caught four times; and as many as 30 were caught two or three times within a 2-month period. Additional material from rabbits from southern Illinois (Jackson and Union counties) was gathered by Dr. W'illard D. Klimstra of Southern Illinois University and Glen C. Sanderson, the latter employed jointly by the Illinois Department of Conservation and the Illinois Natural History Survey. These collections, together with those gathered from many other areas by Survey staff members, were compared with the data obtained from Lee County in northern Illinois to secure informa- tion on the differences in the seasonal behavior of rabbit ectoparasites within the various climatic zones of Illinois. Illinois, a long state, extends about 3R0 miles from north to south and embraces several climatic and life zones. Cottontails in Illinois are the normal hosts to at least seven species of facultative or obligate ectopara- sites, exclusive of chiggers and other small mites. In- frequently, perhaps accidentally, rabbits of Illinois may acquire other species of ticks and fleas that regularly feed on other mammals, such as ground squirrels, mice, and moles, but these ectoparasites do not usually per- sist on rabbits. Rabbits in the western part of North America are hosts to several more, most of them different, species of ectoparasites than are rabbits in the eastern part, table 1. Often where one species of ectoparasite drops out at the edge of its range, another biologically equiv- alent species takes over and continues into the adja- cent geographical range. There is a sudden change in the kinds of species of ectoparasites on rabbits at about the 100th meridian. Cottontails in Illinois are infested by every rabbit ectoparasite known east of the lOOth meridian except the flea l/oplopsvllus (F.uhoplo- psyllus) e^lacialis affinis (Baker). To date, no speci- mens of affinis have been taken in Lee County or else- where in Illinois. TICKS Haemaphysalis leporis-palustris (Packard); conti- nental rabbit tick, rabbit tick; fig. 2. — When ranked ac- cording to numbers of individuals collected within a period of a year, the continental rabbit tick stands as the principal ectoparasite of cottontails in Illinois. This tick is also apparently the chief carrier from rabbit to rabbit of the organism, Pasteurella lularensis, that produces tularemia, a disease which is invariably fatal to rabbits (Green 1939). Although the continental rabbit tick is common over much of North America and all of Illinois, fig. 3, and is collected frequently by biologists, many aspects of its life history are poorly known. Ke found and others have reported that individuals of this tick feed mostly on the rabbit's head, particularly on and in the ears, on the back of the neck, and some- times around the eyes and nose and under the chin. Hooker etal. (1912) were among the first to publish detailed biological information on this tick. According to their findings in Texas, "The three stages of the rabbit tick have been taken from hosts in nature during all seasons of the year." According to a number of authors, the continental rabbit tick in areas north of Texas, specifically in Okla- Table l.—Distribution of the common ectoparasites of rabbits in the United States, exclusive of chiggers, small mites, and nest inquilines. Species Found Elast of 100th Meridian Species Found West of 100th Meridian Croup North South Ticks Haemaphysalis leporis-palustris Ixodes denlatus Dermacentor variabilis Haemaphysalis leporis-palustris Ixodes spinipalpis Dermacentor andcrsoni Otobius lagophilus Haemaphysalis leporis-palustris Ixodes neotomae Dermacentor parumapertus Ornithodoros turicata Fleas Cediopsylla simplex Odontnpsyllus multispinosus lloplopsyllus glacialis affinis (Apparently rare east of Missis- sippi River; taken from imported Kansas cottontails in New Jersey, Burbutis & Mangold 1956) Cediopsylla inaequalis Odontopsyllus denlatus Hoplopsyllus glacialis affinis Cediopsylla inaequalis Odontopsyllus dentatus lloplopsyllus glacialis ctffinis Hoplopsyllus foxi Bot Flies Cuterebra buccata Cutcrcbra horripilum Cuterebra cuniculi Cuterebra leporivora Cutcrcbra Icpusculi Cuterebra leporivora Cuterebra Icpusculi Lice HaemoJipsus setoni Haemodipsus setoni Fig. 2.—HaemaphysaUs leporis-patustris, continental rab- bit tick, unengorged adult female. This tick is a vector of tu- laremia. The characteristic of sharply pointed, lateral angles near the base of the mouthparts (one indicated by arrow) is distinctive of this tick in all stages. homa, Missouri, Iowa, Montana, and Minnesota, is not equally abundant on rabbits at all seasons, and, further- more, one or more of the stages are often rare to absent at certain seasons. Even in Florida the continental rabbit tick is noticeably less abundant in winter (Ilixon in Eddy 1942). Apparently the more northerly the region the more markedly the populations of this tick fluctuate on rab- bits with the seasons. In Oklahoma (Eddy 1942) and in southern Missouri (Portman 1944), this tick occurs occasionally on rabbits even in midwinter. [3y contrast, in northern Missouri (Portman 1944), Iowa (Joyce & Eddy 1943), Montana (Cooley 1932), and Minnesota (Green et al. 1943), it becomes scarce on or entirely absent from rabbits during the coldest winter months. In Minnesota, Green et al. (1943) found that larvae of llaemaphysalis leporis-paiustris "suffer a relatively enormous loss as compared with the losses among older ticks, and that the total winter mortality can be ac- counted for largely on the basis of deaths of larval ticks." In Iowa, Joyce & Eddy (1943) reported an abrupt decrease to very few larvae on rabbits in November, an absence of larvae in December, and a low prevalence of larvae on rabbits in April, May, and June. Apparently in Iowa, as in Minnesota, many unfed larvae fail to survive the winter. Hooker el al. (1912) observed that under favorable conditions ticks in the larval stage could survive as longas258 days (about 8 months) without feeding. 'I'hey found, however, that most larvae survived for 2 to 7 months. In this study, we found that continental rabbit ticks came out of hibernation earlier in southern Illinois than in Lee County. An observation of winter activity was made by Glen C. Sanderson in Union County, southern Illinois. There he found, on December 21, 19.'i5, an adult rabbit tick feeding on a swamp rabbit, Sylvilagus aquat- icus aquaticus (Bachman). In southern Illinois, adults appeared regularly in some abundance on rabbits at the end of January. Our earliest records of the year for rabbit ticks in Lee County were of adults collected on February 25, 1953, and February 17, 1954. When the warmer weather of spring arrived, increas- ing numbers of both adults and nymphs of the continental rabbit tick were found attached to rabbits in Lee County, fig. 4. I3y mid-April copulating pairs were observed on theirhosts. By July the numbers of adults had decreased. Adults seldom were found on rabbits in Lee County in autumn or the first part of winter. Only one adult was found on these rabbits in fall. This specimen was taken on November 9, 1954. Although rarely on rabbits in autumn and winter, adults were present in the surround- ings and were taken repeatedly in September, October, and November from leaf mold. During the several winter and spring months in which we examined rabbits for ticks in Lee County, we found no larvae of the continental rabbit tick. We learned. Fig. i.— llaemaphysalis Icporis-palustris distribution in Illinois, based on Illinois Natural History Survey records. however, of a record of larvae from a towhee, Pipilo erythrophlhalmus, collected on May 14, 1951, at Zion, a northeastern Illinois town near the Wisconsin border. Dr. S. Charles Kendeigh, an ornithologist at the Univer- sity of Illinois, believed that, because of the late date, this towhee was a resident bird and had not recently arrived. It is possible that the towhee acquired the ticks at Zion rather than from some southern area. Seemingly, the larvae on the towhee survived a northern Illinois winter in an unfed condition. Larvae began to appear on rabbits in Lee County in the latter half of July or in August, table 2 and fig. 4. We have records of one earlier appearance, on June 25, 1954, in Lee County and one on July 5, 1946, in central Illinois, (IMIS collection*). Larval ticks reached the peak of their abundance on rabbits in Lee County in August and September. Heavy concentrations of larvae on rabbits ended abruptly in late October or early November, their disappearance coinciding with the beginning of deep frosts and colder weather. * Illinois Natural History Survey collection. Natural Re- sources Building, Urbana, Illinois. Table 2.— Number of larvae, nymphs, anH cottontails examjnetl in Lee County, Illinois; adults of the continental rabbit tick. Ha also, the average number of each stage emaphysalis leporis-pal ustris , taken from of the tick per rabbit examined. Number Average Number of Ticks of Num ber of Ticks Taken Per Rabbit Examined, Month Year Rabbits Examined 1952-1954 Larvae Nymphs Adults Larvae Nymphs Adijlts January 1952 — — _ _ 1953 9 0.0 0.0 0.0 1954 1 February 1952 _ _ 1953 113 1 0.0 0.0 0.1 1954 40 20 March 1952 _ ^ _ ^ 1953 11 89 123 0.0 8.0 11.2 1951 - - - - April 1952 _ __ 1953 5 14 133 0.0 2.8 26.6 1954 - - - — May 1952 4 2 6 1953 12 195 104 0.0 12.3 6.9 1954 - - - — June 1952 52 36 221 1953 9 17 142 0.01 1.5 6.7 1954 6 1 50 87 July 1952 13 2 1953 63 852 26 173 10.6 0.4 2.5 1954 4 6 23 August 1952 15 260 39 3 1953 8 173 5 7 19.6 4.0 0.4 1954 5 116 69 2 September 1952 77 2,433 922 1 1953 — _ — _ 31.6 12.0 0.01 1954 - - - - October 1952 74 7 64 n 1953 72 388 957 3.1 7.0 0.0 1954 19 117 146 November 1952 37 6 11 1953 38 21 63 0.3 0.88 0.01 1954 2fi 11 15 1 December 1952 _ _ _ 1953 2 0.0 0.0 0.0 1954 - - - - TOTAL 715 4,385 2,726 1,049 UJ o < en u 5 50 - i^ 40 z o o o q: 30 ui Q. OC UJ CD 20 - 10 - LARVAE WM NYMPHS ADULTS /^ ■^ sK-Vvy<>p;><><5< ^ <^ ^^ 5^ <^ A ;sr' ^" ;5- >:? c$^ -^ / / .CD' o^ ^ ^- ,o- - k/ O P <<7 Fig. 4. Lee County, —Monthly average of larvae, nymphs, and adults of Haemaphysalis leporis-palustris found on rabbits examined in Illinois, 1952-1954. The graph is based on data in table 2. Nymphs of the year appeared on Lee County rabbits from about the middle of August until about the middle of November, table 2 and fig. 4. They became most abundant in September and the first half of October. Like the larvae, the nymphs became scarce and disappeared from rabbits at the onset of cold weather, but, unlike the larvae, the nymphs commonly survived the winter in a state of hibernation and reappeared on rabbits in the spring. August 1, 1953, vvas our latest seasonal record for a nymph presumed to be of a generation started in the previous year. Because nymphs eventually transform into adults or perish, it is not surprising that a decline in the numbers of nymphs collected occurred in June. Illinois seems to be wholly in the region wherein continental rabbit ticks are generally absent from rab- bits in winter. In Lee County we did not find ticks on rabbits in December, January, or most weeks of Febru- ary, table 2 and fig. .4. In southern Illinois we have a few records of limited winter activity. We have no rec- ords, from any part of the state, of ticks being on their hosts during most weeks of January, the coldest month of the year. On the other hand, it is probable that during warm winter spells some of these ticks, especially those in southern Illinois, may be quick to come out of hibernation to feed. If it were not for literature records of larvae sur- viving the winter in Montana, Minnesota. Iowa, and possibly even Alaska (Philip 1930), we would have suspected from our data that extremely few larvae of the continental rabbit tick can overwinter in northern Illinois. Although some larvae survive, winter cold may take, directly or indirectly, a heavy toll of unted larvae. Apparently, some larvae do not survive much more than a few months in an unfed state (Hooker et al. 1912). Because the larvae in Lee County are probably at least 2 months old by late fall, many of those that have not found a host before the beginning of winter may be sup- posed to perish from starvation. The nonlethal starva- tion period possible for most larvae may terminate at about the time temperatures drop in winter. At this time larvae, numbed by cold and unable to seek a host, may die from lack of food rather than from cold directly. The extent to which cold alone or combined with other factors may adversely affect unfed larvae is an unsolved problem that is worthy of future in- vestigations. Low temperatures may influence adults as well as larvae. Adults of the continental rabbit tick, in both the north and south, go into hibernation or into a period ofrest even before the advent of cold weather. Possibly they require a period of rest or subjection to low temper- atures before they are able to feed, mate, and lay eggs. Such seems to be the case with adults of the eastern rabbit tick, Ixodes dentatus, which, according to Smith (1945), must undergo hibernation in the unengorged state for one winter before they will feed. Similar behavior may be inherent in the continental rabbit tick. If so, the termination of this rest period may come about during the winter. Because of a longer period of low tempera- tures in the north, adults there would necessarily wait longer before seeking a new host than would adults in the south. We made no observations on whether the photoperiod affected the activity of the adults. It is presumed that in Lee County most rabbits become hosts to rabbit ticks at some time, if not many times. For example, between August 11 and August 30, 1952, one rabbit, designated as Peter II, was infested with at least 60 ticks in the following sequence: August 11, 6 ticks; August 18. 13 ticks; August 21, 11 ticks; August 22, ticks; August 25, 10 ticks; August 27, 14 ticks; and August 30, 6 ticks. Other rabbits may encounter continental rabbit ticks as frequently as did Peter II. The proportion of rabbits in Lee County infested with the continental rabbit tick varied greatly with the season. During the periobit flea is the second most numerous ectoparasite of cot- ^ Fig. 8.— Cediopsylla simplex, common eastern rabbit flea, adult female. The presence of a heavy comb of toothlike spines below the eyes distinguishes this species from Odontopsyllus multispinosus. 10 tontails, second only to the continental rabbit tick. Unlike the tick, which is generally absent in the winter, this flea is present on rabbits throughout the year in Lee County. The life cycle and the numbers of generations of this flea per year are virtually unknown. Lwing ^ Fox (1943) stated that one specimen, reared in a vial, passed from the larval stage into the adult stage in less than 3 weeks in the month of April. In general, the common eastern rabbit flea tends to concentrate on the rabbit around the area of the ears. It occurs also on the face, top of the head, and back of of the neck. In rare instances, this flea was found on the back, and occasionally it was taken from some other part of a rabbit's body. Although we examined rabbits during only one entire spring season (1953), and our results should be checked against other collections made in the spring from a greater number of rabbits, perhaps it is worth while to note that a springtime increase of fleas of this species seems to occur on rabbits, fig. 10, In February, 1953, the average number of these fleas per rabbit infested had risen above the average number found in the preceding sunmier and fall. In March of the same year, a sharp increase in average number per rab- bit occurred on the 11 rabbits examined. These fle^s continued to be abundant during April and May on most of the small number of rabbits examined, table 3. For the entire study, the percentage of rabbits carrying these fleas was highest in the period beginning in No- vember and ending in May and lowest in midsummer, table 3 and fig. 10. Approximately 3,000 specimens of the common eastern rabbit flea were collected from rabbits in Lee Fig. 9.—Ccdiopsylla simplex, adult mnle. In this sex, part of posterior protrudes conspicuously. 11 County. Of these, 1,882 individuals were females and 1,060 were males. This distribution of the sexes gives a ratio of 100 females to 56.3 males, or about 2 females to 1 male. Month by month, the ratio remained about the same. The number of males and females carried on any one rabbit varied from many females per male to more males than females. However, when the total popula- tion of fleas present on rabbits each season was con- sidered, the same 2-to-l ratio was observed, even in the springtime when the fleas were suspected to be most actively breeding. Shaftesbury (1934) found a similar ratio of sexes, 100 females to 56.1 males, for this flea in North Carolina. His figures are based on a small number of specimens, 189. The highest number of common eastern rabbit fleas found on one rabbit was 101, collected March 25, 1953. This case was considered unusual; a few other rabbits harbored 70, 80, or even 90 fleas each, but most were less heavily infested. The average number of these fleas per rabbit examined was approximately i. Some rabbits were found to have uo fleas at all, but apparent- ly such a condition is temporary. Table 3.— Number of specimens of the common eastern rabbit flea, Cediopsylla simplex, taken from cottontails examined in Lee County, Illinois, and average number per rabbit infested; also, number and per cent of rabbits infested. Rabbits | Fleas Number Number Mean Per Cent Total Average Number Per Month Year Examined Infested Infested Number Rabbit Infested, With Fleas With Fleas 1952-1954 Taken 1952-1954 January 1952 — — _ 1953 9 8 90 43 5.7 1954 1 1 8 February 1952 _ _ 1953 113 65 70 439 7.4 1954 40 39 330 March 1952 _ _ 1953 11 11 100 366 33.3 1954 - - - April 1952 _ __ 1953 5 5 100 123 24.6 1954 - - - May 1952 4 4 13 1953 12 8 75 205 18.2 1954 - - - June 1952 52 27 104 1953 9 4 54 24 6.0 1954 6 5 86 July 1952 13 5 15 1953 63 24 40 100 4.0 1954 4 3 15 August 1952 15 11 24 1953 8 1 57 1 2.0 1954 5 4 8 September 1952 77 40 150 1953 — — 52 _ 3.7 1954 - - - October 1952 74 37 181 1953 72 39 56 142 4.6 1054 19 17 102 November 1952 37 31 105 1953 38 36 90 202 4.9 1954 26 25 147 December 1952 _ _ 1953 2 2 100 9 4.5 1954 - - - TOTAL 715 452 2,942 12 100 - -50 PER CENT AVERAGE NUMBER ■7 7 — ~r T >^ C" O T 1-40^ h- o o o UJ 1-302 tr UJ - 20 a: UJ CD log < UJ > < Fig. 10.— Monthly distribution (per cent of rabbits infested and average number on infested rabbits) of Cediopsylla sim- plex in Lee County, 1952-1954. The graph is based on 3-month sliding scale of data in table 3. It is interesting to compare the apparent seasonal fluctuations in populations of this flea with populations of other species. Evans & Freeman (1950), in a survey of small mammals occurring near Oxford, England, found that: "For each species of host, the monthly indices point clearly to a rise, not only in the number of fleas per host, hut also in the numbers of hosts in- fested, during the spring, with a maximum reached in the summer and a subsequent decline to a winter low. Such seasonal variation has been observed repeateilly, yet it is by no means clear how much this is due to a real decline in the numbers of fleas present in the breed- ing environment (the nests and burrows of the hosts), how much to a decrease in flea activity, or how much to changes in the numbers or activity of the host popu- lation." Recently, lloldenried et al. (1951) reported marked seasonal fluctuations in two species of fleas in California which have the same mammalian host. They found that the peak of abundance for one flea was in summer and the peak for the other was in winter. Whatever may be the reason for the apparent abrupt increase in numbers of the common eastern rabbit flea on rabbits in Lee County in spring, the time of increase coincides, perhaps significantly, with the main breeding season of rabbits. Presumably, more occupied rabbit nests are present in spring than at any other time of year, a condition which is favorable for the development of a maximum number of larval fleas. 13 Because this rabbit flea has been previously re- corJed in print from only one Illinois locality (Kohls 1940), additional records are marked on the accompany- ing map, fig. 11, to demonstrate its state-wide occur- rence on rabbits. Fig. H.—Cediopsylla simplex distribution in Illinois, based on Illinois Natural History Survey records. Odontopsyllus multispinosus (Baker); giant eastern rabbit flea; fig. 12. — The giant eastern rabbit flea is primarily an ectoparasite of cottontails. Here in Illinois and seemingly elsewhere, this insect is usually less numerous on rabbits than the smaller-sized common eastern rabbit flea. Nowhere throughout its range, from the east coast to about the 100th meridian, has the giant rabbit flea been found to be common. Shaftesbury (1934), in speaking of the North Carolina fauna, stated, "this latter species \_0. multispinosus^ might be rela- tively more abundant on some other kind of rabbit in some other locality." So far, no one has discovered this other kind of rabbit or this other locality. Rather, this flea appears to be the minor rabbit flea of eastern North America and may be scarce to rare on its rabbit host in all regions. In Lee County, this flea was observed only on the backs of rabbits, and most of the specimens were from the lower backs. Apparently the two rabbit fleas divide their rabbit host into territories; that is. the common eastern rabbit flea occupies the front region, head and ears, whereas the giant eastern rabbit flea occupies the hind region. The giant eastern rabbit flea was taken in Lee County during every season of the year. Ninetv-six adult specimens were obtained from 12 rabbits. Inasmuch as more than 700 rabbits were examined, the 12 rabbits infested by this flea represent less than 2 per cent of the population studied. To our knowledge, and as measured by relative abundance, this flea is of little consequence as a rabbit ectoparasite, except perhaps on rare occasions. Once, in late February, 1953, we found a rabbit harboring 74 specimens. Usually each infested rabbit had only one, two, or three individuals of this flea. In the collection of the Illinois Natural History Survey, specimens have been preserved from rabbits at Carbondale, Charleston, Cobden, Elkville, Starved Rock State Park, Urbana, and \'andalia, as well as in Lee County. The records given herein, fig. 13, constitute the first published records for Illinois. Opisocrostis bruneri (Baker). - Single specimens of this ground squirrel flea were taken from rabbits in Lee County on September 22, 1952, and on July 24, October 8, October 11, November 3, and November 8. 1953. This flea was once found on a cottontail in cen- tral Illinois in early April (INHS collection). Ctenophtbalmus pseudagyrtes (Baker). — Although this flea is usually found on moles (Fox 1940). it in- fests many other small mammals, including cottontails. We collected this flea twice from cottontails in Lee County, once on January 2, 1954, and again on October 26, 1954. Orcfiopeas howardii (Baker).- Ordinarily, this flea occurs on tree squirrels. We have two records of it from rabbits, one from Lee County on February 14, 1953, and the other from central Illinois on May 5, 1948. Epitedia wenmanni (Rothschild). — This mouse flea was taken in Lee County from a cottontail on November 9, 1954. BOT FLIES Cuterebra spp.; bot fly; fig. 14. - Bot fly lar\ae were occasionally noticed in open ruptures of the skin of rabbits, particularly in midsummer. In Lee County all but 1 of our 11 records of bot fly larvae were taken from rabbits in July; the exception, a large larva, was found on November 5, 1952. In summer both medium- sized and large larvae were found, even on the same day and on the same host. Cuterebra buccata (Fabriclus). — Six of the bot fly larvae collected from rabbits in Lee County were pro- visionally determined as Cuterebra huccata bv Dr. C. Sabrosky of the United States National Museum. One larva, of large size, collected from a rabbit in Lee County on July 9, 1953, pupated in soil provided for it 14 Vi, Fig. 12.— Odontopsyllus multispinosus, giant eastern rabbit flea, adult female. The absence of toothlike spines below the eyes and the presence of two rows of setae (instead of one row) on each abdominal tergite are features that distinguish this species from Cediopsylla simplex.. and emerged as an adult 2 months later, September 7. The reared adult was determined positively as buccata. Cuferebra cuniculi (Clark) and Cuterebra horripilum Clark. — In the collection of the Illinois Natural His- tory Survey, there are six other specimens of Lot flies; they were taken from Illinois rabbits in summer, 188.3- 1917. Some of these larvae are much larger in size than those found in Lee County and are presumably not Cuterebra buccata. Those that were reared to the adult stage were determined by the late C. T. Greene as cuniculi, a characteristically larger fly than buccata. According to our records, the pupa of cuniculi, unlike the pupa of tuccata, spends about 10 months in the soil. One larva taken in Urbana on July 22, 1890, emerged as an adult on May 22, 1891. Another larva collected from the same locality on August 4, 1890, emerged May 19, 1891. Several of the specimens of cuniculi from central Illinois were from the neck region of cottontails. One of the large unidentified bot fly larvae taken in Lee County may be cuniculi or the closely allied species, horripilum. rather than buccata. CKIGGERS Euschongasfia peromysci (Ewing); Trombicula (Eufrombicula) alfreddugesi (Oudemans); Trombicula (Neotrombicula) whartoni (Ewing). — (^higgers infest a wide variety of mammal and bird hosts. On rabbits they are most commonly attached to the inside of the ears, rhey occur frequently on cottontails in central and southern Illinois, but apparently rarely in the northern part of the slate. Where found in Illinois, Trombicula (Neotrombicula) v/hartoni infests cottontails in late autumn and winter, F.uschongastia peromysci in late winter, and Trombicula (Eutrombicula) alfreddugesi in late spring and summer. Pig. \^,—Odontopsyllus mulHspinosus distrib.ution in Illi- nois, based on Illinois Natural History Survey records. No chiggers were taken on rabbits in Lee County; possibly they were overlooked. CONCLUSIONS Ectoparasites of cottontail rabbits, particularly the continental rabbit tick, llaemaphysalis leporis-palus tris , are significant components of the wildlife of Illinois, and, as such, have had a decided effect on man's activ- ities in recent years. Because of newly gained knowledge of the seasonal behavior of the continental rabbit tick on cottontails, the Illinois hunting laws were changed in 1955. Ecke (1Q4R) and Veatter & Thompson (1952) had shown conclusively, as we found during our studies in Lee County, 1952-19S4, that those ticks which are vectors of tularemia iU'e absent from rabbits in late fall and most of the winter in northern and central Illinois. Postponement of the hunting season until late fall to avoid the tick season and the consequent hazards of tularemia was the logical course of action which fol- lowed the reports of such information. In our limited survey of ectoparasites of cotton- tails in Lee County, we observed the following funda- mental features of the intricate relationships between eclopiu-asite and host: (1) Adults of the continental rabbit tick rarely feed on rabbits in fall. (2) Ticks and fleas reach their greatest abundance at different sea- sons of the year, as if each of the two groups gains an advantage by a division of time on the host- (3) The eastern rabbit flea, Cediopsylla simplex, occupies the head region of its host, whereas the giant eastern rabbit f\ea,Odontopsyllus multispinosus, occupies the back of its host, as if each of the species gains an advantage by eliminating competition for space. (4) The variable wood tick, Dermacentor variabilis, as an adult, is ab- sent from rabbits when, in the same geographical region, it heavily infests other mammals such as opossmns and raccoons. (5) Only two species of ectoparasites, the continental rabbit tick and the common eastern rab- bit flea, are consistently numerous at certain seasons, whereas other ectoparasites, such as Odontopsyllus multispinosus and Ixodes dentatus,\\h\cU are supposedly equally restricted and equally adjusted to rabbit hosts, remain relatively rare most of the time. As is indicatedby the aforementioned observations, the behavior patterns of ectoparasites of rabbits are extremely complicated, \\hat factors, it may be asked, could cause one of the two ticks and one of the two fleas restricted to rabbits to be conmion and the others to be rare? Or what factors could cause the adult of the variable wood tick to infest almost every mammal the size of a rabbit or larger, but not be found on rabbits? Why do the ticks that are primarily ectoparasites of rabbits feed in the adult" stage only on rabbits, vet in the immature stages find birds as acceptable as rabbits? Surveys such as ours cannot provide answers to many questions; rather, they provide a few facts that suggest further questions. Thorough and detailed in- vestigations of the life history and environment of each ectoparasite and the habits and environment of the host need to be undertaken and correlated before much can be deduced as to the origins and the conditions for optimal survival of ectoparasites. Ectoparasites of cottontail rabbits, because they are easy to obtain and because preliminary studies on them have been made here and elsewhere, are worth- while subjects for future research. SUMMARY Seven facultative or obligate ectoparasites were taken from about 700 cottontail rabbits collected in Lee County, northern Illinois, in a period beginning in May, 1952, and ending in November, 1954. The continental rabbit lic\i. Haemaphxsalis leporis- palustris. the principal vector of tularemia, was the most common tick found. \ ery few specimens were col- lected from rabbits from late autumn to late winter. Adults of this tick were collected from rabbits from late winter to midsummer. They reached their great- est abundance on cottontails in spring. The adults rare- ly infested rabbits in autumn or early winter; they were 16 Fig. li.—Cuterebra sp., bot fly larva, dorsolateral view. Actual size about 1-1/4 inches. present, however, in leaf mold, even before cold weather set in. Larvae of this tick apparently suffered high losses during winter, and few were found in spring. In mid- summer, larvae of the new generation hatched and then reached the peak of their abundance on rabbits in Au- gust and September. Nymphs of the new generation reached their peak of abundance on rabbits in September and October. Un- like larvae, nymphs commonly survived the winter and reappeared fairly abundantly on rabbits in early spring. The proportion of rabbits infested with the conti- nental rabbit tick, in any stage, varied with the season. Ninety per cent of the rabbits examined harbored this tick in August and September, per cent in midwinter, 75 per cent in spring, and SO per cent in early summer. The variable wood tick, Dermacentor variabilis, the principal vector in Illinois of Rocky Mountain spotted fever, was found principally in spring, and even then not commonly. Possibly because of the behavior pat- terns of this tick and the rabbit, only larvae and nymphs were found feeding on cottontails in Lee County. The eastern rabbit tick, Ixodes dentatus, although almost exclusively restricted to rabbits, was found to be rare on cottontails in Lee County. The common eastern rabbit flea, Cediopsylla sim- plex, was the flea most often collected. It was found primarily around the head and neck region of rabbits. This flea infested cottontails throughout the year; it was most abundant in early spring and least abundant in late summer. It was observed to have a sex ratio of about 2 females to 1 male. The largest number of fleas of this species found on one rabbit was 101; the aver- age per rabbit examined was approximately 4. On a few rabbits no fleas were found. The giant eastern rabbit flea, Odontopsyllus multi- spinosus, which seemed to prefer to feed on the hind regions of cottontails, was taken occasionally at all seasons. It was not found to be abundant except in rare instances. Fleas of four additional species normally found on other mammals were taken several times on cottontails in the Lee County stuily area. These specimens had probably strayed to rabbits accidentally. Cuterebra buccata was the principal bot fly ob- tained from cottontails in Lee County. Larvae were found, mostly during the summer, in open ruptures of the skin of rabbits. One of the large unidentified larvae may prove to be cuniculi or horripilum. No chiggers were found on the rabbits examined. 17 LITERATURE CITED Bell, J. F., and W. S. Chalgren 1943. Some wildlife diseases in the eastern United States. 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Smith, Carroll N. 1945. Biology of Ixodes denlalus Neumann (Ixo>•» '<•■>•■ i ( • ' 5-; c . • : -; '" , ' ' F ,-' • "'■ ■ • i , . : • *■ i,j»' '>*■,■• '^-.r