September 18, 2011

Great Meadows Mystery Insect

Dogwood Sawfly larva (Macremphytus testaceus), final instar

On today's Great Meadows walk we encountered a swamp dogwood shrub crawling with caterpillar-like larvae - powdery white above, yellow below, with a black head.  Having first met these creatures last fall, memory failed me yesterday when trying to recall their identity.  The larvae will seek rotting wood or debris within which they can make their cocoons to overwinter.  The emerge in the spring as adult sawflies who will seek out fresh dogwood shrubs on which to lay their eggs.

Sawflies are related to bees and wasps, but their larvae look remarkably like caterpillars, with some physical and behavioral differences.  Sawfly larvae always have more than six pair of prolegs (soft, unsegmented legs) along their abdomens, while caterpillars never have more than five pair.  Sawfly larvae often appear in large numbers on a single tree or shrub and seem prone to congregate together in interesting justapositions and poses (eg., above).

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