Acta Veterinaria Scandinavica 2008, 50:14 http://www.actavetscand.com/content/50/1/14 the moose population (at least up to 66°N), including the Helsinki area. The specimens, preserved in 70% ethanol, were investi- gated using existing keys and descriptions [1,2]. Results and discussion The three larvae were about 26–27 mm long and 7 mm wide, and therefore definitively in their third and last instar. According to descriptions published [1,2], the third instar larvae of C. ulrichii is distinguished from C. stimula- tor and C. trompe by having spines irregularly placed on the anterior dorsal side. The spines on C. stimulator and C. trompe are placed in regular rows similar to those on the ventral surfaces. The posterior peritremes were also dis- tinctive. All the larval characters coincided with the description of C. ulrichii (Figures 1 and 2). Generally, all Cephenemyia species are very host specific and thereby also well adapted to their hosts. This host spe- cificity is a product of the fine balance between parasite and host, and the adaptations made by the parasite to sur- vive in the host [12]. In most cases, when an unusual host has been successfully attacked by an oestrid, the parasite will normally not develop properly. This, however, depends in part of how closely the aberrant host is related to the usual host. In the present case, roe deer and moose belong to the same family (Cervidae), although they differ considerably in size. Third instars of C. ulrichii reach a length of 40 mm, whereas the specific throat bot fly larvae of roe deer, C. stimulator, reaches a length of 30 mm [1,2], probably reflecting a restriction imposed by the size of their host. The larvae in the present study seemed to be nearly fully grown and were probably ready to exit the host for pupa- tion in a few weeks. The date of the find, 4 June, is proba- bly in the middle of the exit period of the larvae. We therefore suggest that these larvae would have succeeded in developing in this aberrant host. The smaller size may either be because the larvae were not fully grown, or that the unusual and smaller host prevented the larvae from growing larger. If C. ulrichii larvae in roe deer are not able to reach full size, we could expect failure in pupation proc- ess or high mortality/deformation in the adult stage. It has also been observed that if larvae are taken from the host before they are mature, they often fail to pupate [13]. In the Oestridae, some species have only one host species, whereas others parasitize two or more (often closely related) host species [14]. There are several cases reported of other oestrids with seemingly successful development in unusual hosts. The reindeer warble fly, Hypoderma tarandi, has been found to develop into mature larvae in red deer [15], in moose [15,16], and in musk ox (Ovibos moschatus) [17,18]. C. ulrichii is regarded as very host spe- cific for the moose [1,2], and development in aberrant hosts has apparently never been reported before. The only published reports we can find where C. ulrichii has attacked other species than moose, are a case in which first instar larvae were found in the conjunctival sac in the eye of a human [19], and another case where 39 young larvae were deposited by a female C. ulrichii on the upper lip of a human [1]. In continental Europe, several large surveys on the throat bot flies on roe deer have been performed (e.g. [20]), but only C. stimulator has been reported. Rein- deer throat bot fly larvae have been found in the nasal cav- ities of dogs in Sweden [21]. Further, a middle-aged woman with ophthalmomyiasis described that while picking forest berries in eastern Fin- land, she got a big fly in her eye, which was subsequently affected. Following removal, the parasites were morpho- logically identified as 1st instars of probably C. ulrichii (Sakari Jokiranta and Sauli Laaksonen, unpublished). Conclusion These unusual oestrid – host relationships in Cervidae and other animals, including humans (see review [22]), lCFueisgpcuhaerpnere1moluyisa, dulorircshaiil tvhieirwd instar larvae from roe deer Capreo- Cephenemyia ulrichii third instar larvae from roe deer Capreo- lus capreolus, dorsal view. Note irregular rows of spines on the anterior dorsal side. Anterior end is the thicker one. lCFueisgpcuhaerpnere2moluyisa, vuelrnicthriailthviredwinstar larvae from roe deer Capreo- Cephenemyia ulrichii third instar larvae from roe deer Capreo- lus capreolus, ventral view. Note the more regular rows on the anterior ventral side. Page 2 of 3 (page number not for citation purposes)