Thursday, 16 April 2015

Awesome bee flies

Bee flies, Bombylius major have emerged in the warm weather and I have come across them in several places. Bee flies are early spring fliers, the peak of adult activity is in April and May. They are found throughout the UK, where this species seems to be expanding north. Thee are some cool facts about them.
A male at rest.
Parasitism. Bee flies are parasitoids of several species of ground-nesting solitary bees, including Andrena mining bees. Their larvae crawl into the bees' nests and feed on larvae of the host bee once it is fully developed. Only large populations of mining bees are able to sustain a parasitoid population, so the presence of the bee fly is an indicator of healthy mining bee populations.
Female loading her sand-brush
Egg shooting. Bee flies collect sand or dust at the tip of their abdomens (which looks a bit like a brush) to coat their eggs before laying, as the one above is doing. Why? It is unclear if it is to camouflage them or to make them heavier. Females lay eggs in a curious way. Instead of just getting into the bee nest to lay, they fly low over bee aggregations, and throw their eggs against dark spots resembling nest entrances, including shadows swinging their bodies against it. Bee flies can afford some inaccuracy when egg laying though, as females can lay thousands of eggs per day. Their unusual egg laying behaviour might have something to do with the fact that they are soft-bodied insects, and could be too susceptible to the bee's sting to actually risk a one-to-one confrontation with the female bee. This is how they do it, note the sand-brush at the tip of the abdomen:


Mimicry. As their name strongly suggests, Bee flies are flies that look like bees, that is they are bee mimics like many hoverflies: they are similar in size to a honeybee, brown-tawny and as furry, with quite long hairs, as a bumblebee. It is unclear though if they mimic bees to get close to their nests unnoticed or to avoid predation from insect eating birds or other predators. Other mining bee parasites do not resemble bees at all (I'm thinking the wasp-like Nomada bees) and actually get inside nests to lay eggs.
Look into their eyes. You can tell male and female bee flies in the same way that hoverflies: males eyes are larger and actually meet a the top of the head, while in females they are smaller and separated by a hairy patch. This suggests that males use the sense of vision to look for females. Males actually hover in particular spots some times high up, near flowers, possibly to meet females.
 
male
female
Male feeding on Lungwort showing the fully extended tongue
Look at that tongue! One of the most impressive features of bee flies are their proboscis. These spear-like, non-retractable structure at the front of their head looks positively dangerous (like a giant mosquito!), however, it is harmless, its only purpose is to allow the fly to reach and suck nectar from flowers with deep, narrow corollas. Their mouth parts can be extended further as they feed to as long as their total body length.
A male feeding on grape hyacinth on Monday
Fantastic fliers. Bee flies are very fast and agile fliers, they hover a lot and can fly in any direction, including backwards. They don't settle to feed on flowers like hoverflies, instead, they behave more like a Hairy footed flower bee, or a Hummingbird Hawkmoth: their wings never stop moving when they feed from flowers, they are actually virtually invisible. They use their spindly legs to stabilise themselves in front of the flower. Males will hover at height, as many hoverflies do, and spin when they meet females.
Bee fly feeding on primroses on Monday
Pollinators. Bee flies feed on early spring flowers: Primroses, Grape-hyacinths, Forget-me-Nots, Violets, Lung-wort, Lesser Celandines and Wood Anemones. They will also feed on Blackthorn and sallows. Bee flies not only feed on nectar, they also consume pollen, with females feeding on pollen to a larger extent than males. They can be effective pollinators of these early plants.
A basking Bee fly yesterday.
Basking. Bee flies are active in warm, sunny days, and they like to bask to thermoregulate, sitting still, with their wings kept open at an angle. Then, you can try and identify the species as the wing patterns - hard to see in flight - can be diagnostic. The most common species, the large bee fly, Bombylius major, has a distinctive dark edge at the front of their wings.

More information
An identification sheet of British Species by the BRC. Click here.

Natural History Museum page. Click here.

Boesi, Roberto, Carlo Polidori, and Francesco Andrietti. "Searching for the right target: oviposition and feeding behavior in Bombylius bee flies (Diptera: Bombyliidae)." Zoological Studies 48.2 (2009): 141-150.

Jacquemyn, Hans, et al. "Biological flora of the British isles: Primula vulgaris Huds.(P. acaulis (L.) Hill)." Journal of ecology 97.4 (2009): 812-833.

12 comments:

Phil said...

Brilliant post about a wonderful insect. Watched one today feeding on bluebells, hovering underneath and holding the edge of the flower, then probing upwards.

Midmarsh John said...

Great photos.

I was trying to photo and video these for my blog a few days ago. I have noticed their numbers increase over the past few years.

Africa Gómez said...

Thank you Phil! It is amazing what having this tongue allows them, they act more like bees than like flies too!

Africa Gómez said...

Thank you John, yes, I saw my first one two years ago, and, fortunately, they seem to be staying around and I see more each year too.

leafencounterwp said...

How very interesting. I thought the bee fly somehow laid their eggs directly onto the bee, as I've seen the fly chase the bee when both are hanging around the same flower patch....

Africa Gómez said...

Hi Leafencounterwp, An interesting observation too. Maybe Bee-flies chase bees to find their nesting aggregation? I

leafencounterwp said...

I'll have to keep a sharper eye on them, see where they go - but they fly so fast, it's quite easy to lose sight of them!

leafencounterwp said...

Further to the fly chasing the bee activity.. I was chatting with the person I'd originally observed this behaviour with, and told him about this post.. He wondered if the fly might also flick its eggs at the bee in order that the bee would unknowingly carry the eggs directly into its nest.. ?

Africa Gómez said...

Hi Leafencounter, interesting hypothesis! however, the egg flicking behaviour has been studied in detail, and not aimed at bees, instead to their nests (or shadows, which the bee-fly interprets at nests. The writer of the article on egg flicking said a bee fly aimed eggs to the crack between his shoe and the soil!

RayHolden said...

I've learnt a lot from this article!

Although I'm yet to see any in S. Yorkshire, I see them in London and the SE in early/mid April.
The most common early host plant I find is Borage - that is where I first find them (on April 6 this year https://flic.kr/p/r33dhJ ) ,
with Grape Hyacinth/Muscari favoured as they venture further afield.

Africa Gómez said...

Hi Ray, I'm glad you enjoyed the post. I saw them in Hull in 2013 for the first time and not last year. This year I have seen them in several places in East Yorkshire, and several people have noticed this too. Maybe you'll get them near you in the not too distant future! And thank you for the link at Flickr!

lotusgreen said...

I'm so glad to discover your blog. I'm in Berkeley, California, and am trying to learn more about the less-seen (by me, anyway) stages of like moths, butterflies, ladybugs, etc. The ladybugs, I have seen the larvae and the pupa, and even the shedding of the pupa, but never the eggs. So much to learn! Thanks for being here!