#cluster fly

Cluster Fly - Pollenia sp.

When I first uploaded this drab looking specie of Fly to the blog last year, I had only found one on the leaves. With a name like “Cluster Fly”, you would expect many individuals grouping closely together and hanging around to enjoy the warmth of a new spring. While I can honestly say that the Flies I found weren’t exactly super close to each other, the warm afternoon weather caused many individuals to come outside and swarm around. It was hard to get a moment’s peace outside with Fly after Fly landing on me or nearby and needing to be shooed away. It wasn’t quite a cloud, but there could’ve been at least 20 Flies nearby, and maybe more if some flew away and others took their place! If this is what they’re like outside, just imagine what happens when they hide away in confined spaces during the winter such as inside houses! Have no worries because as pesky as Cluster Flies sound, they only enter houses to escape the cold. When winter arrives, they enter diapause and await the end of winter to become active again: with their metabolism slowed down, they won’t breed. Even if they wanted to breed indoors, Clusters Flies seem to rely on parasitizing earthworms with their eggs. Maybe if have any potted indoor plants you might want to check the soil if you’ve seen adult Flies near them. 

A bigger problem that’s been reported with Cluster Flies is if they were to die indoors they may draw other predators indoors in search of an easy meal. Before searching your homes (inside and out) for a potential cluster invasion, remember that there are always signs you can watch for and ultimately they aren’t as big a pest as other types of Flies. They don’t tend to spread filth (beyond any germs in soil) and they feed on pollen from flowers rather than rotting material or garbage. I’d still recommend you wash your hands after handling them, and speaking of handling them, this is the first time I’ve ever stuck a finger out to a Fly and it actively climbed aboard. These insects aren’t skittish and react much slower compared to Blowflies or Hoverflies. While this makes me appreciative for the closer look at them, I do fear for their safety if they are sluggish aren’t predators. Perhaps the summer broods have more speed to spare, but if there is evidence to support that, I have yet to see it. If I find any answers, I’ll create a follow-up post, but these Flies tend to be overshadowed during the summer by the other flower-loving Fly species.

@mildlavasauce submitted: zebra fly?? found in indiana, usa

Maybe we should call them zebra flies! They do have very nice stripes. It appears to be a common flesh fly, though, in the genus Sarcophaga, which is a really fun and spooky genus name. The different species look pretty dang identical though so I couldn’t say which one it is!

Bug of the Day

The other day when it was warm-ish, I went out to hunt for bugs to photograph, and the only live thing I found was this cluster fly (Pollenia sp.), sitting on top of a giant pile of snow, three feet from the door I came out of :-).

Cluster Fly - Pollenia spp.

Insect life has returned to Toronto’s outdoors once again! While we could stand to have a few more warm days in a row and more consistent sunny weather (with occasional rain), I think it’s fair to say that spring has arrived. At the very least, the insects are taking advantage of the sun and awakening to a new year. It’s only been a few days, but I’ve already seen many species remerge from the leaf litter and into warmth. There have been Firebugs, Honeybees (at flower retailers, very sporadic outside right now as there haven’t been many substantial blooming yet) and Flies, including the specie featured in today’s showcase: the Cluster Fly. This find actually represents a new family of Flies joining the blog: Polleniidae. It seems to once have been subfamily of Blowflies, but was made distinct recently. Year after year, Flies always seem to be the first family of insects that are observed after the thaw, buzzing around in search of resources and mates. There’s certainly plenty to go around since the thaw has exposed leaf litter and other buried, err, treasures. 

Though similar in appearance to Houseflies, Cluster Flies can apparently be distinguished their larger size and by the presence of light and dark patches on their abdomen. Zoom in to see for yourself. For a drab insect, it certainly has color that can be appreciated. Most of the individuals I’ve seen were zooming and buzzing around this foliage filled area, trying to remain in full sun exposure. Gotta stay warm when the wind moves the way it does. Though most Flies are skittish, these Flies didn’t seem too bothered being watched by a human. Though solitary right now, their common name comes from their habit of aggregating at windows come springtime in an attempt to return outside. They try to enter houses as cold weather comes and stay warm in attics. Though an infestation wouldn’t be a pretty sight, it is fortunate that they aren’t a bother to humans otherwise (aside from the occasional feast on food). They don’t lay eggs in houses, instead exclusively laying their eggs in soil so their larvae can feed on earthworms. There’ll be plenty of those as moisture and vitality return to the soil.

AKA grass flies or attic flies. Probably Pollenia pediculata, although New Zealand has at least 30 species - quite diverse compared to the rest of the world.

The family Polleniidae are widespread, and not very well understood. Most species that have been studied are parasites of earthworms, but a few have been recorded from caterpillars and bees.

In cold weather Cluster Flies seek refuge in attic spaces and similar protected areas, emerging again on warm days only to get trapped en masse at the windows.