Sawfly Sunday: Cimbex americana Leach

Wildflower Wednesdays and Sawfly Sundays have been on hold the last few weeks because writing lectures and teaching 14 hours a day at the Museum of Biological Diversity in Columbus, Ohio, have taken precedence. The enthusiasm and industry of the 18 students from Columbia, Germany, Canada, Argentina, South Africa, Spain, and the USA have made this course fun, but I do miss the Home Bug Garden. Similar experiments in urban biodiversity are not obvious among the vast expanses of lawn and concrete here. But the old deciduous street trees in some neighbourhoods (complete with defoliating elm leaf beetles) and the occasional sight of some exotic (at least to an Albertan) like a cardinal, black vulture, or Japanese beetle, and one not so exotic and very scruffy ground hog, provided a bit of natural relief. Now I’m trapped at the airport with a cancelled flight and a looming missed connection – but internet – so time for another Sawfly Sunday.

 Cimbex americana Leach is the largest sawfly that I have ever seen and apparently the largest in North America. Named for its predilection for American elm, a once common street tree in the pre-Dutch elm disease era, the elm sawfly also feeds on willows and the leaves of a variety of other hardwood trees. Although Dutch elm has yet to ravage the elms of Edmonton, none grow near the spot we found this large, wasp-like not-wasp: Elk Island National Park. Perhaps this monster is able to fly long distances, but a more reasonable assumption is that its larval stages were spent on some native like the willows that grow so abundantly in the park. The pale caterpillar like grubs have a black dorsal stripe and grow to 5cm (2 inches) in length, so if you have them on your trees, you are likely to notice them.

 Our elm sawfly very obligingly posed for a few pictures in hand before we returned it to a leaf. Many people would probably respond with a bit of fear and loathing to such a large and scary looking ‘wasp’, but this attractive insect has no real way to do more than pinch your finger with its mandibles. The wasp-like show is just that – all show and no sting (but, of course, a saw instead). BugGuide.net has a lot of pictures of the adults of this highly ornamented species that seems to mimic different wasps in various parts of its broad range. There are about 15 recognized species in the genus including the intriguingly named Button Horn Sheet Wasp (C. femorata). I wonder how it got that name?