When you’re out in your garden or on a nature trail have any little metallic green insects caught your eye? Often it’s the shiny reflection that first captures my attention. If you start looking closely, you will probably see several different types of critters that could be considered “little green jewels” on the plants around us.
Although Japanese beetles have a metallic green sheen, they aren’t all that little and quickly cause noticeable damage to the plants they feed on – so they definitely don’t count as a “jewel” to be viewed with appreciation. The insects that have caught my attention are much smaller, less numerous, are stunningly attractive if you can get a close look at them, and lead rather interesting lives.
There are two species of green leaf weevils in the genus Polydrusus that occur in our area. They are only about ¼ inch in length and their bodies are completely covered with round, shiny, emerald green scales that give them a rather granulated appearance. Both of these European introductions feed on the foliage of many different types of deciduous trees such as birch, apple, poplar and maple as adults.Their larvae feed in the upper soil layers on the fine roots of the same tree species the adults feed on. The impact of the larval feeding isn’t known, but the nibbling of the adults on the leaf margins rarely causes problems, except possibly on very young trees. P. sericeus, the green immigrant leaf weevil, has more conspicuous linear black grooves on its elytra, has relatively larger eyes, and is slimmer than its relative P. impressifrons, the pale green weevil. P. sericeus is a generalist feeder, but birch is its preferred food. They are sometimes found on fruit crops, and because they are noticeable people may be concerned that they are pests, but they’re generally just moving in from other trees and won’t cause any significant damage.
Watch flowers for bees about 3/8 inch long with a metallic green head and thorax. This is a pollen-feeding halictid bee which is one of many bees that are important as native pollinators, especially in light of the decline of the domestic honeybee. Only the females collect pollen, using brushes of hairs called “scopae” on the hind legs to store the grains for the trip back to their nest.
A green bee that also has a black and white striped abdomen is likely Agapostemon virescens. Both males and females of this species have a striped abdomen, whereas only the males of other species in this genus have stripes (the females of other species are wholly metallic green, but also rather hairy). There are several species of these ground nesting bees in Wisconsin. They are typically communal nesters with up to several dozen females sharing the nest, depending on the species.
They dig a common burrow entrance, usually with a little mountain of excavated soil nearby. The tunnel usually goes straight down into the ground for a ways before branching off laterally in many places. These side tunnels may also be branched, and at the end of each tunnel is a single cell. The females provision their own cells with pollen that they’ve collected from lots of different types of flowers, and then lay an egg in the cell. The larva that hatches will complete its development by eating that provisioned pollen, with no further contact with its mother. Gardeners are often unwittingly responsible for habitat destruction for these types of ground-nesting bees, when we mulch everything in sight. That’s great for moisture retention in the soil and suppressing weeds, but mulch may impede these digging insects from finding a place to make their homes and raise their young.
Finally, you may have noticed small, skittish flies sitting on leaves of various plants that quickly dance away when something approaches. If you move slowly you may be able to get close enough to see their long legs, big eyes, and wings held out to the sides before they flit away. These are dolichopodids, or long-legged flies, part of
a large family of true flies with more than 7,000 described species worldwide. Most have a metallic sheen in hues of green, blue, copper, gold, or silver and many have patterned wings. They are predators or scavengers of other smaller insects, both as adults and larvae, so you can appreciate them as beneficial insects in the garden!
They are also common, but frequently overlooked, in grasslands, woodlands and wetlands. But they are also not well known and it’s not easy to identify them, so getting a positive ID is usually not practical.
I find a little ¼ inch green one, probably in the genus Condylostylus, sitting on the leaves of my bean plants every year in the vegetable garden (as well as on other plants elsewhere in the yard). There are many others around commonly, including larger, non-colorful species.
These are just a few of the many interesting insects that occur right under our noses. If you start looking, you can probably find many other tiny insects that would qualify as interesting “jewels” of the garden!
– Susan Mahr, University of Wisconsin – Madison
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