BR. J. ENT. NAT. HIST.,4: 1991 65 MATE-GUARDING IN EPHYDRA RIPARIA FALLEN (DIPTERA: EPHYDRIDAE) I. F. G. McLean 109Miller Way, Brampton, Huntingdon, Cambs. PE18 8TZ. OnS.viii.1989attheedgeofasaltmarshpoolnearAldeburgh, Suffolk(TM461546) 1 found a pair of flies belonging to the family Ephydridae with the male mounted on the dorsal surface ofthe female. 1 took five close-up photographs ofthese flies, one ofwhich is reproduced here (Plate III Figure 4). While observing the two flies through theviewfinderofthecamera I noticed that themalewas not in copulawith thefemale, but ratherridingon herdorsalsurfaceinaposturecharacteristicofmate- guarding behaviour. After spending perhaps 5 or 10 minutes stalking and photographingthe flies, theywerecapturedandsubsequentlydeterminedasEphydra riparia Fall., using the key by Collin (1963). A variety ofmate-guarding strategies are reviewed by Thornhill & Alcock (1983) including some adopted by members of the Diptera. I have not been able to trace any pubhshed references to mate-guarding in Ephydridae, though observations of matingbehaviourin whataretypicallysmall fliesarelikelytobedifficult. Recently, Dyte(1988)published adetailedaccountofmate-guardinginHydrophorusoceanus (Macq.) (Diptera: DoHchopodidae) another saltmarsh species, where the males are muchsmallerthanthefemales andpossess raptorial forelegswhichgraspthethorax ofthefemale.Additionally,amale-biasedsexratiowasrecordedinH. oceanus, which is in accordance with other insects which adopt mate guarding behaviour. Ephydra ripariadoesnothaveanyobviousmorphologicaladaptations formateguardingandthe sexesareofasimilarsize. Itwouldbeofinteresttoinvestigatethesexratiointhisspecies andto make moredetailed observations ofthe pre- and post-copulatory behaviour. References Collin, J. E. 1963. The British species ofEphydra(Dipt., Ephydridae)Entomologist'sMon. Mag. 99: 147-152. Dyte, C. E. 1988. Mateguardingand sexratio inHydrophorusoceanus(Macquart)(Diptera: DoHchopodidae) The Entomologist 107: 122-126. Thornhill, R. &Alcock, J. 1983. Theevolution ofinsectmatingsystems. Harvard University Press, Cambridge, Massachusetts. PLATE III. 1-3. Some interesting European spiders. F. M. Murphy. 1991. Br. J. Ent. Nat. Hist. 4: 69-76. 1.Macrothelecalpeiana. 2.Patpimanusorientatiseating Tegenariaagrestisinthe letter's web. 3. Lycosa tarantula. 4. Mate-guarding in Ephydra riparia Fallen (Diptera: Ephydridae). I. F. G. McLean. Br. J. Ent. Nat. Hist. 4: 65. Pentax ME Super, 100mm f4Takumar macro lens setatf32, total 150mm extension with -I-3 diopter close-up lens, Olympus T28 twin-head macro flash, Agfa CT100 colour reversal film.