Eric Carle understood butterflies. His book, The Very Hungry Caterpillar, featured a “tiny and very hungry caterpillar” that ate a wide variety of different foods before spinning a chrysalis, emerging a couple of weeks later as a lovely multi-coloured butterfly. If only all caterpillar stories were as fun!
Several weeks ago, you read about last summer’s very hungry scourge, the LDD (Lymantria dispar dispar) moth. It’s been renamed to remove a racial slur, and is now called the Spongy Moth, after the appearance of the light brown egg masses laid on trees, outdoor furniture, poles, and other hard surfaces.
The caterpillars hatch out of these fuzzy patches in the spring, at about the same time that tree leaves grow. The tiny black caterpillars (2 mm long) may be carried by the wind up to one kilometer. They are most active during May and June, eating oak, sugar maple, birch, spruce, and aspen leaves. One caterpillar may eat up to one square meter of leaf matter. Their appetite increases as they grow and eventually the caterpillars are 5 to 6 cm long. They’re dark and hairy with five pairs of blue and red dots on their backs.
In late June and July, the caterpillars transform into dark brown pupae. After one to two weeks the adult moths emerge and live for about two weeks. Males are brown with dark markings. The flightless females are white with dark markings. Adults do not feed; their only goal is to reproduce. Females stick the eggs together in a fuzzy, spongy mass that may contain 100 to 1,000 eggs. The egg masses remain through the winter.
Outbreaks of Spongy Moths are part of the natural cycle, and many die from viruses and fungus attacks. But what can homeowners do when there’s an outbreak? There are a few strategies that will reduce the number of these very hungry caterpillars from destroying neighbourhood trees.
In spring, scrape the egg masses off trees and other solid surfaces into a container. Dump the contents into a large bucket of water with some liquid dish detergent added. Leave them for at least two days to be sure all the eggs are dead, then strain out the solids. Dispose of the material in a plastic bag in the garbage. Be sure to wear gloves to avoid a rash from the fuzzy coating. Don’t scrape them onto the ground – they’ll still hatch.
Once they hatch, the caterpillars will move down to the ground during the day to avoid predators and sun. The fine hairs on the caterpillars’ bodies are a skin irritant and may cause a nasty rash. Wear gloves to squish them, or pick them off the trees and drop them into a bucket of soapy water. Leave them for at least two days to drown, then strain out the corpses. Apparently, they make a satisfying crackle and pop when tossed onto a bonfire, but if that’s not an option they should be placed into a plastic bag and added to your regular garbage.
In addition, traps may be constructed with sheets of burlap. Cut a piece to go completely around the trunk of the tree at chest height. Use twine to tie it around the middle of the sheet, then fold the upper half down over top of the lower half. It makes a sleeve around the tree. The caterpillars will climb over it on their way down, but when returning up the tree many will become trapped in the folded burlap. Lift the flap of fabric to reveal the trapped caterpillars. Wearing gloves, pick them off the underlying sheet of burlap and drop them into that very useful bucket of soapy water. Check it daily. You may also be able to collect female moths this way!
Residents with woodlots won’t be able to pick individuals off trees, due to the overwhelming numbers that may be involved. There are sprays that may be applied over larger areas. Contact a local conservation authority to see if there is a program that you and your neighbours may use to try to minimize the damage to your woodlots.
Dumping the eggs into a bucket of soapy water
Healthy deciduous trees (oak, maple, birch, poplar) can survive up to three years of defoliation by Spongy Moths. They will regrow tougher less nutritious leaves to make it harder for the moths to survive. Trees that are stressed may not survive, however. Sadly, evergreen trees like spruce and white pine may not survive for more than one year. Your best defense is to keep your trees healthy.
Natural controls can help to lessen numbers. Prolonged cold winter temperatures below -26C and poor snow cover will kill off egg masses. Cool, wet spring weather is perfect for the fungus Entomophaga maimaiga to thrive in the soil, infecting and killing many moths.
The best defence is a good offence. Get ready now, with gloves, scrapers, buckets, detergent, burlap, and twine. Check trees and patio furniture for egg masses. Lay burlap traps once the leaves are out. And keep a bucket of soapy water next to your gardening gloves. With some effort now, you may be able to keep those very hungry caterpillars off your trees.