Little reed beetle (Plateumaris pusilla)
This week’s crawly reminds us that if we take the time to look close at nature – really, really close – we will be rewarded.
Meet the little reed beetle (Plateumaris pusilla) also known as the tiny swimming reed beetle.
At just barely over one-quarter of an inch in length, the “tiny” part of their moniker is sure accurate.
The “reed” and “swimming” parts of their common name give you a lot more information on these wee metallic beauties.
Little reeds are in the Subfamily Donaciinae AKA aquatic leaf beetles. So if you want to spot one of these jewel-like beetles you will need to spend time along the margins of ponds, streams and lakes. That’s not a tricky task here in our area.
Of course, as nature loves a niche, not just any pond, stream or lake will do.
Reed beetles are either monophagous or oligophagous.
No need to break out your Merriam Webster’s (though you can if you want to) – monophagous (mon-off-eh-gus) means eating or using only one type of food. Oligophagous (oh-liff-eh-gus) means eating only a few specific kinds of foods.
Both are a fun tongue twister-y way of saying these pretty, bitty beetles have host plants.
The favored fare of reed beetles – including our pictured little reed beetle – are either sedges (Cyperaceae) or reeds (Juncaceae) with sedges the clear favorite.
Fear not: The little reeds’ narrow diet will not cause them to have problems finding that favored food. We have 169 different species, subspecies and varieties of sedges growing here in the Pacific Northwest.
Now we’ll delve into the lifestyle of the little reed and it is truly amazing and unique!
Although they can fly, adult little reed beetles are never far from sedgey waters. Adults feed on nectar, so they will flit from flower to flower pollinating as they go.
When it’s time to get working on the next generation, females (who are slightly larger than the males) will use their nifty shovel-like, flattened ovipositor to lay eggs on the stems of the host sedges (another common name is spade reed beetles).
When the eggs hatch, the little larvae scootch underwater and feed off the host plant, hiding in the sediment around the plant roots.
But wait, there’s more! The kiddos also tap into the plant stems for oxygen, creating their own snorkels as it were.
When it’s time for teeny tiny reed beetles to build their cocoons for their final morph into adulthood they have quite a different method of weaving that other larvae who spin silk or similar material.
Tiny reed beetles build snug cocoons around themselves with secretions produced by symbiotic bacteria which live in the foregut of the larvae (in people that’s the area between your esophagus and the opening to your tummy).
It’s like reed beetles have a live-in and super handy probiotic!
As adults, males don’t host any of the nifty bacteria; they don’t need to. Adult females, however, host the bacteria further down the digestive line, so they can deposit the bacteria on their eggs and the next gen will have the bacteria once they hatch.
Seriously! All this awesomeness in one tiny and very sparkly metallic beetle! Keep an eye on a sedge or reed near you this summer!
