Seasonal and spatial changes in blowfly production from small and large carcasses at Durham in lowland northeast England

Colonization by blowflies (Diptera: Calliphoridae) of mouse carcasses expos ed in open agricultural land near Durham (54 degrees 45'N) changed from ear ly spring monopolization by Calliphora vicina R.-D. to a summer pattern of multiple species exploitation by this species together with Lucilia caesar L., L. illustris Mg., L. silvarum Mg., L. sericata Mg. and L. richardsi Col lin. In a garden at the edge of Durham, mouse carcasses were dominated by C. vic ina from spring to autumn. Difference in mouse colonization between the agr icultural and garden sites seemed to reflect differences in the blowfly spe cies present, as measured by baited trap catches at the sites. In sets of C. vicina reared from mice under conditions of competition for l arval food, it was found that resulting females were significantly larger t han males, size being measured as mean wing length. Blowfly production from three sheep carcasses exposed successively at the a gricultural site was dominated by C. vomitoria L, and L. caesar, but also p roduced other Lucilia species in small numbers, including L. sericata. Thes e L. sericata females from sheep that had died from causes other than myias is included full-sized specimens, in contrast to those produced from mouse carcasses that were all undersized individuals. As L. sericata females trap ped on sheep pastures are predominantly full-sized, this suggests that larg e carcasses may, in part, be a source of the L. sericata population that at tacks sheep as a myiasis agent. The nature of large carcasses as possible s ources of L. sericata in lowland Britain is discussed.