Calliphoridae

Blowflies (2) - 'greenbottles'

DIPTERA > BRACHYCERA | Higher Diptera

MUSCOMORPHA > SCHIZOPHORA > Calyptratae > Oestroidea > Calliphoridae > Luciliinae

It seems rather strange now to think that through virtually all of my adult life I've simply referred to the colourful metallic green flies that would regularly be found in the kitchen when I was growing up as 'greenbottles'. That's what my mother called them and, as with 'bluebottles', I'd never given any consideration to the fact that there could be different species. Obviously, that changed once I started becoming interested in Diptera yet, even with my new knowledge, I get the impression that a lot of people who observe flies don't try to identify them and are happy that they can collectively be called 'greenbottles'.

There are seven described species on the British List but, despite being widespread and easily recognisable as 'greenbottles', they are poorly recorded. This is quite surprising given that they can mostly be identified from external morphology although, that said, there are quite a few features that are probably not going to be clearly visible in photos. And, of course, I'm referring here to putting a name to the species for personal use, not official recording where the specimen would need to be properly examined under a microscope.

The males of most species can usually be identified with a reasonable degree of certainty, but many of the females will require closer examination. In conjunction with some of the important features noted below it's also useful to pay attention to where these flies are seen as well as the general habitat can provide a good indicator. Not all the time, but it can certainly help with some species.

Although seven species are listed, there's one that's very rarely recorded, and that's Lucilia bufonivora, which is a specialised parasite of toads. If I ever see one, I'll add more information, but suffice to say that they're not a toad's best friend!

Before looking at the individual species, it's worth noting that the males can be separated into three groups simply by the distance between their eyes. The 'common greenbottle' Lucilia caesar has its eyes set very closely together, almost touching. In that respect alone, it could only be confused with Lucilia ampullacea. The equally common Lucilia sericata has much wider spacing with the distance between almost twice the width of the third antennal segment. A head on view is great for gauging the separation as you can directly compare the spacing with the antenna. This also applies to the other species, Lucilia illustris, Lucilia silvarum and Lucilia richardsi, which have eyes separated by roughly the width of the third segment, or in the case of the latter slightly more.

Another good visual feature is the colour of the wing base, known as the basicosta, which is a pale, creamy white colour in Lucilia richardsi and Lucilia sericata, but dark in all the other species.

Lucilia caesar - under-recorded, but the most frequently encountered Lucilia in most areas. Fresh individuals are iridescent green but, as with most of these species, the colour soon fades becoming somewhat coppery and then often turning bronze with age. They have a dark basicosta and two pairs of postsutural acrosticals. The males have a very narrow frons with the silvery-white orbits of the eyes nearly touching, a character only shared with Lucilia ampullacea. Females can't be officially distinguished from Lucilia illustris without partial dissection to examine the ovipositor, but large individuals with dark wing bases are almost certainly this species. Lucilia caesar can be found in various habitats where it can often be seen resting on vegetation or sunning itself in a sheltered spot.

Lucilia sericata - one of two species with a creamy-white basicostae although, in that respect alone, it can't be reliably separated from Lucilia richardsi without close examination of the genitalia. However, the females are distinctive as they have a particularly wide frons, noticeably wider than any of the other species, with the black interfrontalia being almost twice the width of the silvery-white orbital plates which themselves are broader than the width of the third antennal segment. They can also be recognised by having a conspicuous pale grey dusting on the tergites and a single anterodorsal bristle on the mid-tibia. The males also have wider spaced eyes than any of the other species, separated by almost twice the width of the third antennal segment. Lucilia sericata is a generally widespread species that prefers sunny and open habitats, particularly in urban or suburban areas, but also around farms where it is often associated with sheep. It is also frequently found on rubbish dumps, dead animals, faeces, meat and fruit, and is the most likely 'greenbottle' species to find indoors.

Lucilia richardsi - a poorly recorded species with females that are very similar to Lucilia sericata except that they have a distinctly narrower frons and eye spacing. The males' eyes are also more closely set, separated by slightly more than the width of the third antennal segment. They also have a pale-coloured basicosta but, apart from the difference in their eye spacing which can be subjective, they can be distinguished from Lucilia sericata by having two anterodorsal bristles on the mid-tibia. The females have less heavily grey dusting on the tergites and, apparently, proportionally longer antennae than typically evident in Lucilia sericata. Although this species is regarded as widespread and frequent on downland and, as such, should be found in Dorset, the last official recorded sighting was over fifty years ago. So, could I have photographed one in the garden - well, the pale basicosta, more closely separated eyes and, importantly, two rather one anterodorsal bristles, suggests that I did.

Lucilia ampullacea - officially, you'd need to check the lack of a coxopleural streak on the side of the thorax in front of the rear spiracle to reliably confirm the identity of this species. But, visually in the field and subject to the light, they can often be distinguished simply by their general appearance as they tend to retain a bluish, somewhat teneral, colouration. Otherwise, the males resemble Lucilia caesar, but without the large genital capsule of that species. It is the most shade-loving Lucilia and the most likely species to be found in wooded areas or around scrub.

Lucilia silvarum - commonly known as the Marsh Greenbottle as it has a strong association with wetlands or any other damp places where there are amphibians which their larvae parasitise so, in that respect, it could well be found in similar habitats to the Toad Greenbottle, Lucilia bufonivora. It's a localised, rarely common species, with few records even though it has some key features that should make it relatively easy to identify. It has dark wing bases the same as a couple of the other species, but can be pretty much distinguished by usually having three rather than two pairs of postsutural acrosticals - the same as Lucilia sericata, except that species has creamy-white basicostae. But, it's also different in that the first visible tergite (tg1+2) is distinctly blackish, a feature that as far as I'm aware is only shared with Lucilia bufonivora. The males' eyes are separated by roughly the width of the third antennal segment, and the females have a frons that's about one third the width of the head which is roughly the width of an eye.

Lucilia illustris - although averaging a little smaller than Lucilia caesar, the females of these two species cannot be confidently separated without internal examination as previously noted. The males though, have a combination of dark basicostae with a relatively wide frons where the silvery-white orbits are clearly separated by the black interfrontalia. Interestingly, Lucilia illustris is the third most frequently recorded species after Lucilia caesar and Lucilia sericata yet, in theory, it's probably the most difficult species to identify from photos.