Bee With a Green Head: What You Are Actually Looking At

Metallic green almost always means one of three things: a sweat bee, an orchid bee if you are in the American tropics, or — surprisingly often — a fly. The first is by far the most likely in a temperate garden.

Telling them apart

The quickest test is the eyes. A fly’s eyes are enormous and often meet over the top of the head. A bee’s are small and set at the sides, leaving an obvious face between them.

The second quickest is hairiness. Bees carry pollen and are built for it — even the sleek ones have branched hairs. A bottle fly is smooth and hard-looking, like enamel.

Sweat bees, properly

Halictidae is a large family, and the metallic green members are the ones people notice.

• Size: small. Quarter to half an inch — much smaller than a honey bee.
• Nesting: mostly in the ground, in bare well-drained soil, sometimes in rotting wood. Some are solitary, some share a nest entrance in loose communal groups.
• Season: active early spring to late autumn, which is the point — they cover the gaps at either end of the year when honey bees are not flying.
• Behaviour: non-aggressive, do not swarm, do not defend a hive because most of them do not have one.

The sting, and the landing

They land on people for salt and moisture in perspiration — hence the name. They are after the sodium. It is harmless and most noticeable on hot days doing physical work outside.

The sting itself is very mild — commonly rated at the bottom of the scale, well below a honey bee, and gone in a few minutes. Males cannot sting at all, which is true of every bee species: the sting is a modified egg-laying organ.

Why they are worth having

Sweat bees are serious pollinators, and in several respects better than honey bees for a garden:

• They fly in cooler and duller conditions than honey bees will.
• They are active earlier and later in the season.
• They pollinate a wide range of wildflowers, fruit and vegetables, including some crops honey bees handle poorly.
• They are native, unlike honey bees across most of the Americas.
• They carry pollen loose and dry on body hairs, which makes them messier and therefore better at transferring it.

Encouraging them

The important part is the one most gardens get wrong.

• Leave bare soil. Most sweat bees are ground nesters, and they need sunny, well-drained, undisturbed bare patches. A garden mulched to the last inch has nowhere for them to nest, and a bee hotel drilled for cavity nesters does not help them at all.
• Leave a dead log or stump for the wood-nesting species.
• Skip the insecticides, particularly systemic ones, which persist in pollen and nectar.
• Plant a long succession of open flowers — asters, coreopsis, sunflowers, goldenrod, mint-family herbs, native wildflowers. Small bees need shallow, accessible flowers.
• Do not fill in their holes. Small neat holes in a dry sunny bank in spring are usually ground-nesting bees, not an infestation.

If they are genuinely a nuisance

Rarely worth acting on, but if a communal nesting patch is in a spot people use constantly:

• Water the area. Ground-nesting bees want dry soil, and regular irrigation makes a site unattractive without killing anything.
• Mulch or plant over that specific patch, leaving bare soil somewhere else.
• Wait. Most are active for a few weeks, and the adults you see now are gone before long.

Insecticide is the wrong answer for an animal that is not defending a hive, stings barely, and is doing more for the garden than most things in it.