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.

Thursday, 9 April 2015

Buzzzzzzz!!!!!

There was definitely a buzz in the garden today. The usual Anthophora plumipes males were now joined by the first female of the year (above), feeding on the Pulmonaria. The Pulmonaria, unfortunately, was in the shade, so I couldn't take as sharp photos as I would have liked. A male Osmia bicornis (previously rufa) was patrolling the grape Hyacinths and a female Andrena fulva made a brief appearance. Just on cue, as the Cherry, a favourite of this bee, started to bloom yesterday.
 A Green Shieldbug was out sunbathing, also the first of the year. Many young wolf spiders were out too in the sun, stalked by my young cat, who likes to hunt and eat them, to my dismay. A Peacock butterfly passed by, but didn't settle.
Unidentified Andrena sp. on a dandelion.
Male Osmia bicornis
Male Anthophora plumipes.
Green shieldbug
Flea beetle, Altica sp.



Tuesday, 7 April 2015

A late start of spring

Despite the mild winter, spring is taking a while to start. It has been very windy and cool of late. The last few days have been noticeably milder and still, almost warm when the sun came out. My first Anthophora plumipes male came out on the 12th of March, a bit late, but not unusual. Then there has been a few queen bumblebees and honeybees. The striking thing is that I haven't seen a butterfly this spring yet. A queen wasp bumped against the conservatory window a few days ago, but I couldn't identify it to species. Today, I found a very sluggish queen Common Wasp, Vespula vulgaris, inside the conservatory. Spring is slowly, but surely, on its way.

Monday, 16 February 2015

Garden Centre Spider (II)

Another visit to the garden centre. I spend much of it looking up most, in search for the Garden Centre Spider, Uloborus plumipes. I must have been a funny sight. My efforts are rewarded quickly. First, and most obvious I spot the webs, stretched across the plumbing by the glasshouse roof. They are laid almost horizontally and is an orb web. This one had a stabilimentum, a decoration in the centre of the web, in this case a linear one.
The spiders were a bit harder to find. After a while I saw some piece of debris hanging from some web, see the spot in the middle of the photo?
Zooming in, it revealed itself a a superbly camouflaged spider. It is hard to think it is a spider from a distance. Once I had spotted one, more followed, and I counted five in a relatively small area. 
The nicer thing, though, was to find its spiky egg sac too.
Sorry for the poor photo quality, but the spiders were 3 m above me and the light already fading.

Sunday, 8 February 2015

Sunbathing Nursery web spider

A sunny day, we visit the wildlife garden. We find little in the way of invertebrates, but, as we are about to leave, on the south facing Ivy, I spy this young Nursery Web spider, Pisaura mirabilis, which makes my day. First she is sitting like some wolf spiders or crab spiders, sometimes sunbathe, with their front legs curled up, looking very relaxed. Then she seems to detect my presence, and it stretches out her front legs in the more typical position of the species (above).