It looks like a bee and sounds like a bee... but it's not a bee

I've written about mimicry of bees by flies before, in context of syrphid flies. Syrphid flies are generally considered Batesian mimics, which means, broadly speaking, that they mimic a more harmful creature. In the case of syrphid flies, they are mimicking stinging insects like wasps and bees, and thereby get to piggyback on the anti-predator defenses of those species. This kind of mimicry can only work if the creature being mimicked signals its ability to harm a predator in some way that can be imitated.

What I'm writing about today is a bit different. I managed to snap a picture of a bumble bee-imitating robber fly last week in my local ravine park. Although it's possible that the bumble bee-imitation confers some anti-predation advantages to the robber fly through Batesian mimicry, something else is probably also going on here: Wicklerian-Eisnarian mimicry. The idea with this kind of mimicry is that an organism imitates a less harmful one in order to avoid detection by its prey. Robber flies prey on other insects, including bees; looking a lot like a bumble bee is probably a pretty good way to get close enough to their prey to kill them, since bees are nectar and pollen eaters rather than insect eaters. From the perspective of many insects, a bumble bee is no particular threat, while a robber fly is definitely worth avoiding.

There are many other types of mimicry besides these two, as well. I was rather pleased to get a picture of a bee mimic that isn't a pollinator but rather a predator. Pretty neat! They also sound a lot like bumble bees, interestingly, so the mimicry goes beyond visual cues in the case of this robber fly, which I think is in the genus Laphria, and which has caught an emerald ash borer (Agrilus planipennis). Robber flies consume their prey by piercing their bodies with a hardened tube that serves as their mouth, through which they inject their prey with some digestive enzymes and then suck out the delicious bug juice that results.

Laphria sp. consuming Agrilus planipennis (sorry for the crummy cell phone camera photo)

Mmm, bug juice.

Syrphid Flies - Syrphidae

I have mentioned syrphid flies before on my blog, usually when mentioning the pollinators of a given plant. But what's a syrphid fly?

"Syrphid fly" refers to an entire family of insects, the Syrphidae, which are bee and wasp mimics. They resemble bees or wasps, which confers some of the natural defenses and safety that would be accorded those more dangerous species that they emulate.

Many syrphid flies are nectar and pollen eaters, and so will be attracted to flowers and provide pollination services. Many of these species are not nectar-robbers but pollinators, though we don't necessarily think first of flies when we think of pollinators.

This family is quite large and diverse. I am not, for the most part, able to identify particular species of syrphid fly. Sometimes it is obvious that two individuals belong to different species; other times, it takes close observation.

There were quite a lot of syrphid flies visiting the flowers of the insect gardens in the Montreal Botanical Gardens. They were mostly of the same size and shape, so probably the same genus. It wasn't until later when I was looking at my photographs that I realized that there were multiple species. Take this one here:

Syrphid fly

 This one has dark eyes, and a stripey abdomen which transitions from yellow to red at the tip.

Syrphid fly

This second one (I posted this photo yesterday for the discussion of Rudbeckia hirta), on the other hand, has red eyes, and a yellow patterned abdomen.

Likely these are two different species (I say likely because I am not certain of this; it is theoretically possible that there might be extreme polymorphism in a single species, but unlikely).

As I was looking through the photos another thing jumped out at me. In that first photo, the syrphid has a strange, bulgy yellow protuberance between its eyes. I wondered what it was: mouth parts? A sensory organ of some sort?

So I trotted down to reddit and asked the helpful entomologists on /r/whatsthisbug about it. I was told that that yellow protuberance is actually the antennae, which are frequently heavily modified in syrphid flies. So. Syrphids can have very strange-looking antennae indeed.