Ottawa is in the throes of a gypsy moth caterpillar infestation! 

At this stage, the caterpillars are probably descending from the leaves at night and resting on the ground or at the base of the tree so checking your tree from 5 pm until dark and even after dark with a flashlight will net you a good haul of 2-3 inch caterpillars.  Then check the tree again in the morning when it starts to warm up:  7:30-9 am is a good time.  And, if you can, checking during the daytime also helps because the caterpillars will move around.  

This moth has 5 stages of caterpillar growth (instars) if a male and 6 if female (she eats more to lay down fat to produce her 300+ eggs later this year).

As of mid-June, we are about half- to three-quarters of the way through the caterpillars’ eating phases and as one caterpillar eats up to one square metre of leaf surface between hatching and pupating, it is important to continue monitoring our trees.  

The caterpillars will start to pupate any time now from late June or early July; this is a good time to look for the brown hard-cased pupae and flick them into a pail of detergent and water along with any remaining live caterpillars. Check any surface: walls, tires, car wheel wells, eaves, undersurface of branches and especially the trunks of trees.

The adults will emerge from the pupal cases in August, mate (the adults fly in search of females, the females normally do not fly) and the female lays the eggs in a yellow soft and furry mass.  At that point, we should begin the egg scraping and destruction process all over again.  

Pluck the caterpillars off your plants/trees and drop them into a bucket of soapy water.  Cover and let soak for up to 48 hours before safely disposing of the dead caterpillars.  

It is not too late to wrap trees in burlap or any breathable fabric or with a combination of sticky tape with shiny tape top and bottom.  Use string to hold the burlap in place.  The caterpillars will crawl under the burlap at night.   Safely dispose of any caterpillars that you catch. 

When handling the caterpillars, wear gloves as the hairs carry a histamine that can provoke an allergic reaction similar to poison ivy.  As the caterpillar goes from one instar to the next, the cast skins break down and the hairs are blowing around. So wear long-sleeved shirts and long pants and maybe even a hat when out walking or controlling the caterpillars.  Seek medical attention if the blisters are severe.  

Adopt a tree in Stanley Park and other wooded areas around New Edinburgh! In parks or street trees, mark the burlap with your name or initials (so others know that you are returning to remove the caterpillars) and check your adopted tree as many times a day as you can.  Eighty to 90 per cent of a tree’s defoliation occurs during the 5th and 6th instars when the caterpillars have reached their maximum size and so it is worth it to remove as many as possible now and over the next two weeks.

As a last resort, spray trees/plants with Btk (Bacillus thuringiensis kurstaki).  Ideally consult a professional. 

Additional information on gypsy moths, including how to deal with current caterpillar infestation, can be found on the City of Ottawa website.

All is not lost for the defoliated trees. WATER YOUR TREES frequently but DO NOT add fertilizer to the water or sprinkle fertilizer around the tree. Leaf loss is a stress and combined with this spring drought, the impact is doubled. Fertilizer promotes new woody growth but you want leaves only.

-Iola Price and Tamara Miller