The Birds and Bees of Oaks Bottom — field guide

Green Sweat Bee

Agapostemon sp. · family Halictidae · about 10mm

When: April – October | Where: the meadow, the bluff trail, and any garden with open flowers

The two sexes look like different species

This is the bee I would point at if someone asked why a field guide should show both sexes. Most guides pick one and move on. Look at what that would cost you here.

Female green sweat bee, metallic green from head to tail — **The female** — metallic green from her face to the tip of her abdomen. Photographed on an overcast afternoon, which is the only reason the colour survived.

Male green sweat bee with a green head and thorax and a gold-and-black striped abdomen, on a pale aster — **The male** — green head and thorax, but a gold-and-black striped abdomen. Same species. Nothing behind him but open sky.

Green from head to tail means female. A striped abdomen means male. There is no overlap and nothing subtle about it — which is why anyone shown only one of these photographs would walk away with half the animal.

How to tell it apart

From other metallic bees: she is entirely green, and a solid, unmissable green — not a faint sheen. The small metallic sweat bees in the same family are duller, often bronzy or blue-tinged, and considerably smaller. If you can see the colour clearly from a few feet away without leaning in, it is this one.

From a fly: two pairs of wings, not one, and long segmented antennae rather than short bristles. Hoverflies mimic bees convincingly and are common on the same flowers.

Two things worth knowing

The name is literal. Sweat bees are called that because some species in this family will land on human skin to drink perspiration — they are after the salt. They are not aggressive about it and they very rarely sting.

They are solitary bees that live next door to each other. Agapostemon often nest communally: several females share one burrow entrance in bare ground, then each digs and provisions her own cells off the shared tunnel. No queen, no workers, no shared labour — just a common front door. It is an apartment building rather than a colony.

Photographing her

It took me five sessions of about three hours each to get a photograph of the female I was happy with, and the thing that finally worked was an overcast day.

A metallic bee behaves like polished metal rather than like a feather. In direct sun, a small hard light source blows the green into pure white highlights and the colour disappears into them. Cloud turns the entire sky into an enormous soft source, and instead of one blown hotspot the colour reads right across the curve of her body.

If you are using flash, a large diffuser held close does the same job on demand — it is a portable overcast sky. That is the trick with any iridescent insect: make the light source big.

Prints and downloads: the female on cosmos · the male on an aster

Read more: The Bees Next Door — the longer piece on the native bees of this neighbourhood, with fifteen other species.