Large Rose Sawfly from the UK

Subject:  What is this
Geographic location of the bug:  Handworth middlesex
Date: 06/27/2018
Time: 07:52 PM EDT
Your letter to the bugman:  Can you identify this it was on my rose not seen one before
How you want your letter signed:  Wayne

Large Rose Sawfly

Dear Wayne,
This is a Large Rose Sawfly,
Arge pagana.  Sawflies are non-stinging relatives of Bees and Wasps that have larvae that are frequently confused for caterpillars.  According to Garden Safari:  “The Large Rose Sawfly is a quite beautiful and shiny animal. The animal is entirely black, except for the abdomen which is yellowish orange. Because of the dark, blackish wings, which are kept over the abdomen, the orange colour may not always be clearly visible. The legs are usually entirely black as well. The animals are not capable flyers, slowly flying about with the legs hanging down. In flight they are quite similar to to some flies, such as the St Mark’s Flies, appearing in spring as well. Males can be told apart from the females by looking at the antennae. Males have wire-like antennes, which are the same size just about everywhere. Females have antennae which get slighter thicker going upwards. The Large Rose Sawfly is on the wing in spring and early summer mainly. Depending on the temperatures most are seen from March to June. Like all Sawflies female Large Rose Sawflies are in possession of a little saw. With it they make rectangular cuts in the fresh shoots of the host plant. In the cut a bunch of eggs is being deposited. The larvae hatch quite quickly and move in a group to the freshly emerged leaves. Young larvae stay together for quite some time, capable of eating the entire shoot. Older larvae lead a more single life and eat from older leaves as well. The larvae are very similar to caterpillars and green with black dots and points. When they feel threatened they assume the so-called S-position. This can be seen in many other sawfly larvae as well. To pupate a firm whitish cocoon is spun near or in the soil. The cocoon actually has two covers. The inner one is smooth and firm. The outer cover has the design of a net. It is the pupa overwintering. The larvae are found on wild and cultivated roses. ”  According to iNaturalist:  “The larvae are gregarious and live in colonies feeding on rose leaves.”

Very interesting! How much damage can they do and all so I found a mint Beatle that was nice to look at and thank you for your answer kind regards Wayne

Hi again Wayne,
We have no personal experience with the Large Rose Sawfly, but from what we have read, the damage is done by the female laying eggs and by the larvae eating leaves.  A large infestation might defoliate a rose bush, but leaves will grow back.  A healthy rose bush should have no problem surviving a small infestation.

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