Tussock Tiger Moth

We’re more used to seeing the Monarch caterpillars munching away on the milkweed. This summer, they have been slow to make an appearance: the cooler than usual temperatures in July had an effect on them.
These beautiful caterpillars, who turn into stunningly beautiful butterflies, are not the only milkweed munchers around.

Yesterday, Aaron, Danzi and Jordy found these fuzzy ones snacking on the jewelweed and milkweed by the Lodge main door. They are sociable, so it's easy to find several of them together. These are tussock tiger moths in training, and they are totally cool.

The milkweed tussock caterpillar or milkweed tiger moth, is a moth in the family Arctiidae. (you can look it up!) They are one of 260 different species of tiger moths found in North America, and are a common mid to late summer feeder. Unlike monarchs, they don’t limit themselves to milkweed on the menu. Ours were also nibbling away quite happily on Jewelweed. The milkweed, however, is the ticket if you don’t want to end up on a menu yourself -- and the toxins they ingest from the milkweed provide a chemical defense against predators. Their vivid colouration helps to advertise this to hungry birds. The defense mechanism lasts into their adult phases as well – when the moths become a food source for bats as well. What toxins, you ask? Well, milkweed contains cardiac glycosides – you don’t want to eat too much of that, and it takes a very high concentration to deter a hungry bat.

Since bats are hunting by radar, and may not notice colouration as a deterent, the moths have upped their game. Both the caterpillar phase and the adult moth have tymbal organs (think, “tympanic”, a bit like your eardrum) on their abdomens. Spring moths use these to listen for the approaching radar “pings” of hunting bats. Late summer and autumn moths, however – those dealing with bats that are very aggressive and hungry because they are feeding their young – use this organ to create a clicking noise. By flexing the tymbal organ, sort of like bending a tiny piece of plastic, they can mimic the radar ‘ping’ of hunting bats. This serves to disorient the bats, and allows the moth a window of opportunity to fold their wings and drop to the ground.

Even these fuzzy caterpillars can create a tiny clicking noise to deter predators, although you’d have to be very close and very quiet to hear them with our ears. Handy little things, tymbal organs, they can also be used to sing love songs during mating season. Pity our own eardrums aren’t quite so multi-purpose!

Some people dislike the tussock (or milkweed) tiger moth caterpillar, thinking that it competes for food with the ever popular and showy Monarch butterflies. In fact, monarchs like to snack on young milkweed. Tussock moths chomp their way through older, mature foliage that wouldn’t be acceptable to the discerning tastes of the monarchs. Eating milkweed is a tricky process all the same, since the plant has its own defense mechanism in the form a sticky “milky” latex sap that can stick your caterpillar mouth shut if you don’t take care. Young caterpillars will carefully avoid eating the veins of the milkweed, turning the leaves into lacy skeletons. Older moths are even more canny creatures – they will cut a vein of the milkweed, so the milky sap runs out along the stem and they can then eat the entire leaf above the cut without all that messiness.

The adult moth has yellowish-gray white wings, with bands of beige on the forewings. The body is ‘hairy’, and yellow, with a row of black dots down the middle of the back. It is this yellow and black colouration that gives the moth the name “tiger.” At rest, they fold their wings like a tent over their bodies, and the wings provide good camouflage.


Tiger moths stick around all winter, over-wintering in fuzzy gray cocoons that can frequently be found if you turn over logs on a hike in the woods.