Birch Sawfly

Sawflies (suborder Symphyta of order Hymenoptera) are the most ancient surviving lineage of Hymenoptera, predating the more familiar wasps, bees, and ants (suborder Apocrita) by approximately 230 million years. The 'sawfly' common name comes from the females' distinctive ovipositor: shaped like a saw with serrated edges, the ovipositor is used to cut slits in plant tissue (stems, leaves, twigs) into which eggs are laid. The cutting-and-laying behavior gives sawflies a unique reproductive strategy that distinguishes them from all other Hymenoptera. Sawfly larvae closely resemble Lepidoptera caterpillars (Lepidoptera evolved their caterpillar form ~140 million years ago, far after sawfly larvae had already evolved a similar body plan) — but the two groups are easily distinguished by the number of pairs of abdominal prolegs: Lepidoptera caterpillars have 5 or fewer pairs of prolegs; sawfly larvae have 6 or more pairs (typically 6-8). Cimbex femoratus, the birch sawfly, is one of the largest sawflies in Europe (adults 25 mm body length) and is known for two distinctive defensive behaviors. First, larvae produce a powdery hydrophobic wax that they spread over their bodies as a protective coating against rain and predators. Second, when threatened, larvae rear up the front of the body and spray a sticky defensive fluid from glands beside the head — similar in mechanism to the velvet worm slime defense, but much smaller scale. Adults are commonly encountered on birch trees in spring and summer across Europe. The species' larvae feed on birch leaves and can defoliate young birch saplings in heavy infestations, but rarely cause significant damage to mature trees.