It's an Elm Zigzag Sawfly Larva! - Observation of the Week, 5/31/20

Our Observation of the Week is this tiny Elm Zigzag Sawfly, seen in Germany by @karsten_s!

“Since my earliest childhood I have been very interested in nature and till today I'm a passionate fish-keeper,” says Karsten Schönherr. He’s made several trips to South America fo research fish, and is currently focused on “the Lithoxini, a group of catfish that lives in the river rapids of the Guyana shield with several still undescribed species.”

With a trip to South America not possible at the moment, Karsten tells me he’s now focusing on local flora and fauna in Germany, utilizing his camera’s macro and telephoto lenses to help him out. “I'm basically broadly interested in mostly everything that I can capture with my camera but particularly focusing on plant-animal interactions, parasitic/parasitoid relationships, Hemiptera, Lepidoptera & Tenthredinoidea,” he says. 

That third taxon is also known as “typical sawflies”, which is what you see above. Karsten found it while on a bike ride, when he stopped along the river Neckar. 

[I] took my camera with the new macro lens (Pentax Lumix DMC-GX80, Olympus Makro 30mm) and checked in the trees nearby if I can find anything interesting to photograph. Obviously there was also this elm tree… I was right away amazed by this regular feeding pattern and tried to make some good pictures. Light conditions were excellent.

Native to eastern Asia, elm zigzag sawflies were first documented in eastern Europe in 2003, and have since spread across the continent and to Britain, where they were first confirmed in 2017. Its common name originates from its larval host plant (members of the genus Ulmus) and distinctive eating pattern, as it devours leaf material in a back and forth manner, at first between the leaf’s main veins. Older larvae tend to not leave such distinct zig zags. After gorging themselves on elm leaves for 15-18 days, the larvae will then pupate for 4-8 days and emerge as small, dark-colored adults with light-colored legs. No males have ever been found, and it’s believed this species reproduces by parthenogenesis.  

“I stumbled onto iNaturalist website while I was searching for reference pictures of catfish of the families Loricariidae and Callichthyidae,” Karsten (above, in Peru) tells me. 

Step by step I also used it to explore local nature and get a better understanding of nature just outside my doorstep. It's a perfect tool to get into contact with the respective experts and convert a nice picture of an insect larva into something more meaningful. Once you know the correct name you can easily find more information about it and how it interacts with other organisms you have observed. It can be a starting point to explore and understand a tiny puzzle piece of the amazing diversity, complexity and beauty of nature…

Hopefully with observations like this more and more people are getting interested in nature and conserving this treasure for us and the generations to follow.

- by Tony Iwane. Photo of Karsten by Norman Behr. Some quotes have been lightly edited for clarity and flow.

- Here’s some nice footage of an elm zigzag sawfly doing its thing. 

Posted on June 1, 2020 12:16 AM by tiwane